Signal compressing apparatus Number:7,394,973 from the United States Patent and Trademark Office (PTO) owispatent

Title: Signal compressing apparatus

Abstract: An input signal is quantized into a quantization-resultant signal. The quantization-resultant signal is compressed into a compression-resultant signal. The compression-resultant signal is formatted into a formatting-resultant signal corresponding to a predetermined format for a digital recording disc. The formatting-resultant signal includes segments corresponding to user data areas prescribed in the predetermined format. The compression-resultant signal is placed in the segments of the formatting-resultant signal. The formatting-resultant signal is encoded into an encoding-resultant signal of a CD format. The encoding-resultant signal is recorded on a recording medium.

Patent Number: 7,394,973 Issued on 07/01/2008 to Ueno,   et al.

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Inventors:	Ueno; Shoji (Fujisawa, JP), Fuchigami; Norihiko (Yamato, JP), Tanaka; Yoshiaki (Fujisawa, JP)
Assignee:	Victor Company of Japan, Ltd. (Yokohama, JP)
Appl. No.:	10/795,297
Filed:	March 9, 2004

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	09985048	Nov., 2001	6741801
	09655046	May., 2002	6393203
	08887216	Nov., 2000	6151442

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Foreign Application Priority Data

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Jul 08, 1996 [JP]			8-197000

Current U.S. Class:	386/98 ; 386/125; 386/126; 386/131
Current International Class:	H04N 5/91 (20060101); H04N 5/00 (20060101)
Field of Search:	386/68,125-126,46,45,131,99,98

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References Cited [Referenced By]

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U.S. Patent Documents

5402406	March 1995	Fuma et al.
5574787	November 1996	Ryan
5627657	May 1997	Park
5675693	October 1997	Kagoshima
5687157	November 1997	Imai et al.
5748594	May 1998	Nishio et al.
5864800	January 1999	Imai et al.
5926448	July 1999	Yokota et al.
6151442	November 2000	Ueno et al.
6393203	May 2002	Ueno et al.
6741801	May 2004	Ueno et al.

Foreign Patent Documents

	8223052		Aug., 1996		JP
	9016199		Jan., 1997		JP

Primary Examiner: Tran; Thai Q.
Assistant Examiner: Chio; Tat Chi
Attorney, Agent or Firm: Connolly Bove Lodge & Hutz LLP

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Parent Case Text

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The present application is a divisional of U.S. patent application Ser. No. 09/985,048, filed Nov. 1, 2001 now U.S. Pat. No. 6,741,801, which is a divisional of U.S. patent application Ser. No. 09/655,046, filed Sep. 5, 2000, now U.S. Pat. No. 6,393,203, issued May 21, 2002, which is a division of U.S. patent application Ser. No. 08/887,216, filed Jul. 2, 1997, now U.S. Pat. No. 6,151,442, issued Nov. 21, 2000.

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Claims

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What is claimed is:

1. A signal expanding method comprising the steps of: receiving an encoding-resultant signal of a predetermined recording-medium format from a DVD, the encoding-resultant signal containing audio information resulting from quantization of an audio signal including a multi-channel audio signal at a quantization degree higher than a degree of quantization for a CD and at a quantization sampling frequency higher than that for a CD; decoding the received encoding-resultant signal into a formatting-resultant signal corresponding to a predetermined format for a DVD, the formatting-resultant signal including segments corresponding to user data areas prescribed in the predetermined format, a compression-resultant signal being placed in the segments of formatting-resultant signal; deformatting the formatting-resultant signal into the compression-resultant signal; and expanding the compression-resultant signal into a quantization-resultant signal by a Huffman decoding process.

2. A signal expanding method comprising the steps of: receiving an encoding-resultant signal of a predetermined recording-medium format from a DVD, the encoding-resultant signal containing audio information resulting from quantization of an audio signal including a multi-channel audio signal at a quantization degree higher than a degree of quantization for a CD and at a quantization sampling frequency higher than that for a CD; decoding the received encoding-resultant signal into a formatting-resultant signal corresponding to a predetermined format for a DVD, the formatting-resultant signal including segments corresponding to user data areas prescribed in the predetermined format, a compression-resultant signal being placed in the segments of formatting-resultant signal; deformatting the formatting-resultant signal into the compression-resultant signal; and expanding the compression-resultant signal into a quantization-resultant signal by one of an orthogonal decoding process and a Huffman decoding process.

3. A computer readable medium encoded with instruction capable of being executed by a computer for storing an encoding-resultant signal containing audio information which is recording on the recording medium by the steps of quantizing an input audio signal including a multi-channel audio signal into a quantization-resultant signal at a quantization degree higher than a degree of quantization for a CD and at a quantization sampling frequency higher than that for a CD; compressing the quantizing-resultant signal into a compression signal by a Huffman encoding process; formatting the compression-resultant signal into a formatting-resultant signal corresponding to a predetermined format for a DVD, the formatting-resultant signal including segments corresponding to user data areas prescribed in the predetermined format, the compression-resultant signal being placed in the segments of the formatting-resultant signal; encoding the formatting-resultant signal into an encoding-resultant signal of a predetermined recording-medium format; and recording the encoding-resultant signal on the recording medium.

4. A signal recording method for recording a recording medium as recited in claim 3, wherein the method comprises the steps of quantizing an input audio signal including a multi-channel audio signal into a quantization-resultant signal at a quantization degree higher than a degree of quantization for a CD and at a quantization sampling frequency higher than that for a CD; compressing the quantization-resultant signal into a compression signal by a Huffman encoding process; formatting the compression-resultant signal into a formatting-resultant signal corresponding to a predetermined format for a DVD, the formatting-resultant signal including segments corresponding to user data areas prescribed in the predetermined format, the compression-resultant signal being placed in the segments of the formatting-resultant signal; encoding the formatting-resultant signal into an encoding-resultant signal of a predetermined recording-medium format; and recording the encoding-resultant signal on the recording medium.

5. An apparatus for an optical disc, comprising: a CD-DA decoder; a DVD decoder; a DVD-audio expansion decoder including Huffman decoding; means for reading out a signal from the optical disc; means for deciding which of a CD-DA, a DVD, and a DVD-audio the optical disc agrees with; means for, when the optical disc agrees with a CD-DA, selecting the CD-DA decoder from among the CD-DA decoder, the DVD decoder, and the expansion decoder and using the CD-DA decoder to process the signal read out from the optical disc into a recovery signal; means for, when the optical disc agrees with a DVD, selecting the DVD decoder from among the CD-DA decoder, the DVD decoder, and the expansion decoder and using the DVD decoder to process the signal read out from the optical disc into a recovery signal; and means for, when the optical disc agrees with a DVD-audio, selecting the expansion decoder to process the signal read out from the optical disc into a recovery signal.

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Description

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BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a signal compressing apparatus such as an audio signal compressing apparatus. Also, this invention relates to a signal recording apparatus such as an audio signal recording apparatus. Furthermore, this invention relates to a recording medium. In addition, this invention relates to an apparatus for an optical disc such as a CD-DA (Compact Disc Digital Audio), a CD-ROM (Compact Disc Read Only Memory), a video-CD, a DVD (Digital Video Disc), a DVD-ROM (Digital Video Disc Read Only Memory), a DVD-WO (Digital Video Disc Write Once), or a DVD-RAM (Digital Video Disc Random Access Memory).

2. Description of the Related Art

The CD (Compact Disc) standards prescribe that the sampling frequency fs should be 44.1 kHz, and the quantization bit number should be 16. There are optical recording discs on which digital signals representing audio information, digital signals representing video information, or digital signals representing both audio information and video information are recorded. Examples of such optical recording discs are a CD-DA (Compact Disc Digital Audio), a CD-ROM (Compact Disc Read Only Memory), a video-CD, and a DVD (Digital Video Disc).

Audio data conforming to the CD-DA standards can not be recorded as audio data of the CD-ROM format for the following reason. The CD-ROM format has headers containing sync information, address information, and mode information. Accordingly, a recording capacity of a CD-ROM which can be used for audio information is smaller than the audio-information recording capacity of a CD-DA.

SUMMARY OF THE INVENTION

It is a first object of this invention to provide an improved signal compressing apparatus.

It is a second object of this invention to provide an improved signal recording apparatus.

It is a third object of this invention to provide an improved recording medium.

It is a fourth object of this invention to provide an improved apparatus for an optical disc.

A first aspect of this invention provides a signal recording apparatus comprising means for quantizing an input signal into a quantization-resultant signal; means for compressing the quantization-resultant signal into a compression-resultant signal; means for formatting the compression-resultant signal into a formatting-resultant signal corresponding to a predetermined format for a digital recording disc, the formatting-resultant signal including segments corresponding to user data areas prescribed in the predetermined format, the compression-resultant signal being placed in the segments of the formatting-resultant signal; means for encoding the formatting-resultant signal into an encoding-resultant signal of a CD format; and means for recording the encoding-resultant signal on a recording medium.

A second aspect of this invention is based on the first aspect thereof, and provides a signal recording apparatus wherein the input signal comprises an audio signal.

A third aspect of this invention is based on the first aspect thereof, and provides a signal recording apparatus wherein the predetermined format for the digital recording disc is equal to a predetermined format for a CD-ROM.

A fourth aspect of this invention is based on the first aspect thereof, and provides a signal recording apparatus wherein the predetermined format for the digital recording disc is equal to a predetermined format for a DVD.

A fifth aspect of this invention is based on the first aspect thereof, and provides a signal recording apparatus wherein the compressing means comprises means for subjecting the quantization-resultant signal to orthogonal transform.

A sixth aspect of this invention is based on the fifth aspect thereof, and provides a signal recording apparatus wherein the compressing means comprises means for subjecting the quantization-resultant signal to a Huffman encoding process.

A seventh aspect of this invention is based on the first aspect thereof, and provides a signal recording apparatus wherein the compressing means comprises means for dividing the quantization-resultant signal into components corresponding to divided frequency bands respectively, and means for compressing the components according to frequency-band-dependent compression characteristics depending on a predetermined auditory sensation model.

An eighth aspect of this invention provides a signal compressing apparatus comprising means for quantizing an input signal into a quantization-resultant signal; means for compressing the quantization-resultant signal into a compression-resultant signal; and means for formatting the compression-resultant signal into a formatting-resultant signal corresponding to a predetermined format for a digital recording disc, the formatting-resultant signal including segments corresponding to user data areas prescribed in the predetermined format, the compression-resultant signal being placed in the segments of the formatting-resultant signal.

A ninth aspect of this invention is based on the eighth aspect thereof, and provides a signal compressing apparatus wherein the input signal comprises an audio signal.

A tenth aspect of this invention is based on the eighth aspect thereof, and provides a signal compressing apparatus wherein the predetermined format for the digital recording disc is equal to a predetermined format for a CD-ROM.

An eleventh aspect of this invention is based on the eighth aspect thereof, and provides a signal compressing apparatus wherein the predetermined format for the digital recording disc is equal to a predetermined format for a DVD.

A twelfth aspect of this invention is based on the eighth aspect thereof, and provides a signal compressing apparatus wherein the compressing means comprises means for subjecting the quantization-resultant signal to orthogonal transform.

A thirteenth aspect of this invention is based on the twelfth aspect thereof, and provides a signal compressing apparatus wherein the compressing means comprises means for subjecting the quantization-resultant signal to a Huffman encoding process.

A fourteenth aspect of this invention is based on the eighth aspect thereof, and provides a signal compressing apparatus wherein the compressing means comprises means for dividing the quantization-resultant signal into components corresponding to divided frequency bands respectively, and means for compressing the components according to frequency-band-dependent compression characteristics depending on a predetermined auditory sensation model.

A fifteenth aspect of this invention provides a recording medium storing an encoding-resultant signal which is recorded on the recording medium by the steps of quantizing an input signal into a quantization-resultant signal; compressing the quantization-resultant signal into a compression-resultant signal; formatting the compression-resultant signal into a formatting-resultant signal corresponding to a predetermined format for a digital recording disc, the formatting-resultant signal including segments corresponding to user data areas prescribed in the predetermined format, the compression-resultant signal being placed in the segments of the formatting-resultant signal; encoding the formatting-resultant signal into an encoding-resultant signal of a CD format; and recording the encoding-resultant signal on the recording medium.

A sixteenth aspect of this invention provides an apparatus for an optical disc, comprising a CD-DA decoder; a CD-ROM decoder; a signal expansion decoder; means for reading out a signal from the optical disc; means for deciding which of a CD-DA, a CD-ROM, and a CD-ROM-audio the optical disc agrees with; means for, when the optical disc agrees with a CD-DA, selecting the CD-DA decoder from among the CD-DA decoder, the CD-ROM decoder, and the signal expansion decoder and using the CD-DA decoder to process the signal read out from the optical disc into a recovered signal; means for, when the optical disc agrees with a CD-ROM, selecting the CD-DA decoder and the CD-ROM decoder from among the CD-DA decoder, the CD-ROM decoder, and the signal expansion decoder and using the CD-DA decoder and the CD-ROM decoder to process the signal read out from the optical disc into a recovered signal; and means for, when the optical disc agrees with a CD-ROM-audio, using the CD-DA decoder, the CD-ROM decoder, and the signal expansion decoder to process the signal read out from the optical disc into a recovered signal.

A seventeenth aspect of this invention provides an apparatus for an optical disc, comprising a CD-DA decoder; a CD-ROM decoder; a signal expansion decoder; an MPEG decoder; means for reading out a signal from the optical disc; means for deciding which of a CD-DA, a CD-ROM-audio, and a video-CD the optical disc agrees with; means for, when the optical disc agrees with a CD-DA, selecting the CD-DA decoder from among the CD-DA decoder, the CD-ROM decoder, the signal expansion decoder, and the MPEG decoder and using the CD-DA decoder to process the signal read out from the optical disc into a recovered signal; means for, when the optical disc agrees with a CD-ROM-audio, selecting the CD-DA decoder, the CD-ROM decoder, and the signal expansion decoder from among the CD-DA decoder, the CD-ROM decoder, the signal expansion decoder, and the MPEG decoder and using the CD-DA decoder, the CD-ROM decoder, and the signal expansion decoder to process the signal read out from the optical disc into a recovered signal; and means for, when the optical disc agrees with a video-CD, selecting the CD-DA decoder, the CD-ROM decoder, and the MPEG from among the CD-DA decoder, the CD-ROM decoder, the signal expansion decoder, and the MPEG decoder and using the CD-DA decoder, the CD-ROM decoder, and the MPEG decoder to process the signal read out from the optical disc into a recovered signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a signal compressing apparatus according to a first embodiment of this invention.

FIG. 2 is a diagram of a first format of a 1-sector-corresponding segment of a digital signal generated by a CD-ROM encoding circuit in FIG. 1.

FIG. 3 is a diagram of a second format of a 1-sector-corresponding segment of a digital signal generated by the CD-ROM encoding circuit in FIG. 1.

FIG. 4 is a diagram of a format of a 1-pack-corresponding segment of a digital signal generated by a DVD encoding circuit in FIG. 1.

FIG. 5 is a diagram of a drive apparatus and a CD-WO (a compact disc write once).

FIG. 6 is a block diagram of a signal compressing apparatus according to a second embodiment of this invention.

FIG. 7 is a block diagram of a signal compressing apparatus according to a third embodiment of this invention.

FIG. 8 is a flow diagram of operation of a signal processing circuit in FIG. 7.

FIG. 9 is a flowchart of a segment of a program related to operation of the signal processing circuit in FIG. 7.

FIG. 10 is a frequency-domain diagram of an example of a signal power, a scale factor, a standard noise level, and an original noise level.

FIG. 11 is a block diagram of a signal compressing apparatus according to a fourth embodiment of this invention.

FIG. 12 is a flowchart of a first segment of a program related to operation of a signal processing circuit in FIG. 11.

FIG. 13 is a diagram of the relation between a code amount adjustment value Adj and a deviation .DELTA..

FIG. 14 is a flowchart of a second segment of the program related to operation of the signal processing circuit in FIG. 11.

FIG. 15 is a block diagram of an apparatus for an optical disc according to a fifth embodiment of this invention.

FIG. 16 is a flowchart of a segment of a program related to operation of a CPU in FIG. 15.

FIG. 17 is a block diagram of an apparatus for an optical disc according to a sixth embodiment of this invention.

FIG. 18 is a flowchart of a segment of a program related to operation of a CPU in FIG. 17.

FIG. 19 is a block diagram of an apparatus for an optical disc according to a seventh embodiment of this invention.

FIG. 20 is a block diagram of an apparatus for an optical disc according to an eighth embodiment of this invention.

FIG. 21 is a block diagram of an apparatus for an optical disc according to a ninth embodiment of this invention.

FIG. 22 is a block diagram of an apparatus for an optical disc according to a tenth embodiment of this invention.

FIG. 23 is a block diagram of an apparatus for an optical disc according to an eleventh embodiment of this invention.

FIG. 24 is a block diagram of a compression encoder in FIG. 23.

FIG. 25 is a block diagram of an expansion decoder in FIG. 23.

FIG. 26 is a flowchart of a segment of a program related to operation of a CPU in FIG. 23.

FIG. 27 is a block diagram of an apparatus for an optical disc according to a twelfth embodiment of this invention.

FIG. 28 is a flowchart of a segment of a program related to operation of a CPU in FIG. 27.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

With reference to FIG. 1, a signal compressing apparatus has an input terminal 1A connected to the input side of an A/D converter 1. The output side of the A/D converter 1 is connected to the input side of a signal processing circuit 2.

A switch 4B has a movable contact and first and second fixed contacts. The movable contact of the switch 4B is selectively connected to either the first fixed contact or the second fixed contact thereof. The movable contact of the switch 4B is connected to the output side of the signal processing circuit 2. The first fixed contact of the switch 4B leads to the input side of a CD-ROM encoding circuit 4A. The second fixed contact of the switch 4B leads to the input side of a DVD encoding circuit 6.

A switch 4C has a movable contact and first and second fixed contacts. The movable contact of the switch 4C is selectively connected to either the first fixed contact or the second fixed contact thereof. The first fixed contact of the switch 4C is connected to the output side of the CD-ROM encoding circuit 4A. The second fixed contact of the switch 4C is connected to the output side of the DVD encoding circuit 6. The movable contact of the switch 4C leads to an apparatus output terminal 4D. Also, the movable contact of the switch 4C leads to the input side of a CD encoding circuit (a CD-DA encoding circuit) 5. The output side of the CD encoding circuit 5 is connected to an apparatus output terminal 5A.

The switches 4B and 4C cooperate to select either the CD-ROM encoding circuit 4A or the DVD encoding circuit 6 as an effective circuit.

A signal generator 3A outputs a clock signal having a frequency of 44.1 kHz. A signal generator 3B outputs a clock signal having a frequency of 48 kHz. A signal generator 3C outputs a clock signal having a frequency of 88.2 kHz. A signal generator 3D outputs a clock signal having a frequency 96 kHz.

A switch 1B has a movable contact, and first, second, third, and fourth fixed contacts. The movable contact of the switch 1B is selectively connected to one of the first, second, third, and fourth fixed contacts thereof. The movable contact of the switch 1B leads to a clock input terminal of the A/D converter 1. The first, the second, third, and fourth fixed contacts of the switch 1B are connected to the output terminals of the signal generators 3A, 3B, 3C, and 3D, respectively. The switch 1B selects one of the output signals of the signal generators 3A, 3B, 3C, and 3D, and transmits the selected signal to the A/D converter 1 as a sampling clock signal.

A switch 7A has a movable contact, and first, second, third, fourth, fifth, and sixth fixed contacts. The movable contact of the switch 7A is selectively connected to one of the first, second, third, fourth, fifth, and sixth fixed contacts thereof. The movable contact of the switch 7A leads the CD-ROM encoding circuit 4A. The first, second, third, fourth, fifth, and sixth fixed contacts of the switch 7A are connected to taps or nodes in a series resistor combination 7B, respectively. The series resistor combination 7B is connected across a fixed-dc-voltage source 7C. The switch 7A selects one of six different voltages available in the series resistor combination 7B, and feeds the selected voltage to the CD-ROM encoding circuit 4A.

For example, the switch 7A can be operated by a user. Operation of the signal compressing apparatus of FIG. 1 can be changed among six different modes. The six different levels of the voltage signal fed via the switch 7A to the CD-ROM encoding circuit 4A are assigned to the six different modes of operation of the apparatus of FIG. 1, respectively. Accordingly, the switch 7A serves as a operation-mode selecting switch, and the voltage signal fed via the switch 7A to the CD-ROM encoding circuit 4A represents an apparatus operation mode desired and selected by the user. Thus, the voltage signal fed via the switch 7A to the CD-ROM encoding circuit 4A is also referred to as the mode signal. As will be made clear later, the switches 1B, 4B, and 4C are linked to the switch 7A.

An analog audio signal is inputted to the A/D converter 1 via the apparatus input terminal 1A. The A/D converter 1 changes the input analog audio signal into a corresponding digital audio signal in response to the sampling clock signal fed via the switch 1B. Specifically, the A/D converter 1 periodically samples the input analog audio signal at a sampling frequency decided by the frequency of the sampling clock signal. The A/D converter 1 changes or quantizes every sample of the input analog audio signal into a corresponding digital audio signal segment (a corresponding audio data piece) with a predetermined quantization bit number. The predetermined quantization bit number is equal to, for example, 16 or 20. The A/D converter 1 outputs the resultant digital audio signal (referred to as the first digital audio signal) to the signal processing circuit 2.

Generally, the input analog audio signal is composed of 2-channel signals. The input analog audio signal may be composed of 4-channel signals, or 6-channel signals.

The signal processing circuit 2 includes a DSP (digital signal processor), a microcomputer, or a similar device having a combination of an input/output port, a processing section, a ROM, and a RAM. The signal processing circuit 2 operates in accordance with a program stored in the ROM.

The signal processing circuit 2 is programmed to compress the first digital audio signal into a second digital audio signal according to a predetermined signal-compression technique including an orthogonal transform process. The predetermined signal-compression technique may also include a Huffman encoding process. In this case, the orthogonal transform process may be omitted from the predetermined signal-compression technique. For example, the predetermined signal-compression technique is selected from among known signal-compression techniques. The signal processing circuit 2 outputs the second digital audio signal (the compression-resultant digital audio signal) to the CD-ROM encoding circuit 4A or the DVD encoding circuit 6 via the switch 4B.

The CD-ROM encoding circuit 4A generates auxiliary information signals (sub information signals) in response to the mode signal. The auxiliary information signals includes a sync signal and a header signal. Specifically, the CD-ROM encoding circuit 4A generates at least a sync signal and a header signal for every sector with respect to a recording medium (a CD-ROM). When the CD-ROM encoding circuit 4A is selected by the switch 4B, the CD-ROM encoding circuit 4A receives the second digital audio signal from the signal processing circuit 2. The CD-ROM encoding circuit 4A combines the sync signal, the header signal, and the second digital audio signal in response to the mode signal on a time-division multiplexing basis for every sector with respect to a recording medium (a CD-ROM). The combination-resultant digital audio signal is of a predetermined format equal to one of the CD-ROM signal formats. The combination-resultant digital audio signal is also referred to as the composite digital audio signal. During combining the signals, the CD-ROM encoding circuit 4A places the second digital audio signal in a time range corresponding to a user data area in every sector with respect to a recording medium (a CD-ROM). When the CD-ROM encoding circuit 4A is selected by the switch 4C, the CD-ROM encoding circuit 4A outputs the combination-resultant digital audio signal (the composite digital audio signal) to the apparatus output terminal 4D and the CD encoding circuit 5.

The DVD encoding circuit 6 generates a header signal for every pack. When the DVD encoding circuit 6 is selected by the switch 4B, the DVD encoding circuit 6 receives the second digital audio signal from the signal processing circuit 2. The DVD encoding circuit 6 combines the header signal and the second digital audio signal on a time-division multiplexing basis for every pack. The combination-resultant digital audio signal is of a predetermined format equal to the DVD signal format. The combination-resultant digital audio signal is also referred to as the composite digital audio signal. During combining the signals, the DVD encoding circuit 6 places the second digital audio signal in a time range corresponding to a user data area or a packet area in every pack. When the DVD encoding circuit 6 is selected by the switch 4C, the DVD encoding circuit 6 outputs the combination-resultant digital audio signal (the composite digital audio signal) to the apparatus output terminal 4D and the CD encoding circuit 5.

The CD encoding circuit 5 converts the output signal of the CD-ROM encoding circuit 4A or the output signal of the DVD encoding circuit 6 into a digital audio signal of a predetermined format equal to the CD-WO (compact disc write once) format or the CD-DA format. The CD encoding circuit 5 feeds the digital audio signal of the CD-WO format or the CD-DA format to the apparatus output terminal 5A.

For example, the CD encoding circuit 5 subjects the output signal of the CD-ROM encoding circuit 4A or the output signal of the DVD encoding circuit 6 to a CIRC (Cross Interleave Reed-Solomon Code) encoding process according to the CD-WO standards or the CD-DA standards. The CD encoding circuit 5 outputs the encoding-resultant digital audio signal to the apparatus output terminal 5A. Specifically, the CD encoding circuit 5 generates an error correction signal in response to the output signal of the CD-ROM encoding circuit 4A or the output signal of the DVD encoding circuit 6, and adds the error correction signal to the output signal of the CD-ROM encoding circuit 4A or the output signal of the DVD encoding circuit 6. The error correction signal uses a cross interleave Reed-Solomon code. The CD encoding circuit 5 feeds the addition-resultant signal to the apparatus output terminal 5A.

Operation of the signal compressing apparatus of FIG. 1 can be changed among six different modes. During the first mode of operation, the switch 1B selects the output signal of the signal generator 3A which has a frequency of 44.1 kHz. The switch 1B transmits the selected signal to the A/D converter 1 as a sampling clock signal. Accordingly, during the first mode of operation, the frequency of the signal sampling by the A/D converter 1 is equal to 44.1 kHz. During the first mode of operation, the switches 4B and 4C select the CD-ROM encoding circuit 4A. In this case, the CD-ROM encoding circuit 4A generates a sequence of a sync signal, a header signal, a sub header signal, a user data block, and an EDC signal in response to the mode signal and the second digital audio signal for every sector with respect to a recording medium (a CD-ROM). The user data block contains the second digital audio signal. During the first mode of operation, a 1-sector-corresponding segment of the composite digital audio signal generated by the CD-ROM encoding circuit 4A has a form such as shown in FIG. 2. The user data block has 2,324 bytes.

During the second mode of operation, the switch 1B selects the output signal of the signal generator 3C which has a frequency of 88.2 kHz. The switch 1B transmits the selected signal to the A/D converter 1 as a sampling clock signal. Accordingly, during the second mode of operation, the frequency of the signal sampling by the A/D converter 1 is equal to 88.2 kHz. During the second mode of operation, the switches 4B and 4C select the CD-ROM encoding circuit 4A. In this case, the CD-ROM encoding circuit 4A generates a sequence of a sync signal, a header signal, a sub header signal, a user data block, and an EDC signal in response to the mode signal and the second digital audio signal for every sector with respect to a recording medium (a CD-ROM). The user data block contains the second digital audio signal. During the second mode of operation, a 1-sector-corresponding segment of the composite digital audio signal generated by the CD-ROM encoding circuit 4A has a form such as shown in FIG. 2. The user data block has 2,324 bytes.

During the third mode of operation, the switch 1B selects the output signal of the signal generator 3A which has a frequency of 44.1 kHz. The switch 1B transmits the selected signal to the A/D converter 1 as a sampling clock signal. Accordingly, during the third mode of operation, the frequency of the signal sampling by the A/D converter 1 is equal to 44.1 kHz. During the third mode of operation, the switches 4B and 4C select the CD-ROM encoding circuit 4A. In this case, the CD-ROM encoding circuit 4A generates a sequence of a sync signal, a header signal, and a user data block in response to the mode signal and the second digital audio signal for every sector with respect to a recording medium (a CD-ROM). The user data block contains the second digital audio signal. During the third mode of operation, a 1-sector-corresponding segment of the composite digital audio signal generated by the CD-ROM encoding circuit 4A has a form such as shown in FIG. 3. The user data block has 2,336 bytes.

During the fourth mode of operation, the switch 1B selects the output signal of the signal generator 3C which has a frequency of 88.2 kHz. The switch 1B transmits the selected signal to the A/D converter 1 as a sampling clock signal. Accordingly, during the fourth mode of operation, the frequency of the signal sampling by the A/D converter 1 is equal to 88.2 kHz. During the fourth mode of operation, the switches 4B and 4C select the CD-ROM encoding circuit 4A. In this case, the CD-ROM encoding circuit 4A generates a sequence of a sync signal, a header signal, and a user data block in response to the mode signal and the second digital audio signal for every sector with respect to a recording medium (a CD-ROM). The user data block contains the second digital audio signal. During the fourth mode of operation, a 1-sector-corresponding segment of the composite digital audio signal generated by the CD-ROM encoding circuit 4A has a form such as shown in FIG. 3. The user data block has 2,336 bytes.

During the fifth mode of operation, the switch 1B selects the output signal of the signal generator 3B which has a frequency of 48 kHz. The switch 1B transmits the selected signal to the A/D converter 1 as a sampling clock signal. Accordingly, during the fifth mode of operation, the frequency of the signal sampling by the A/D converter 1 is equal to 48 kHz. During the fifth mode of operation, the switches 4B and 4C select the DVD encoding circuit 6. In this case, the DVD encoding circuit 6 generates a sequence of a header signal and a user data block (a packet or packets) in response to the second digital audio signal for every pack. The user data block (the pack or packets) contains the second digital audio signal. During the fifth mode of operation, a 1-pack-corresponding segment of the composite digital audio signal generated by the DVD encoding circuit 6 has a form such as shown in FIG. 4. The user data block has 2,034 bytes.

It should be noted that in this specification, a DVD may be another disc in a DVD family such as a DVD-ROM, a DVD-WO, and a DVD-RAM.

During the sixth mode of operation, the switch 1B selects the output signal of the signal generator 3D which has a frequency of 96 kHz. The switch 1B transmits the selected signal to the A/D converter 1 as a sampling clock signal. Accordingly, during the sixth mode of operation, the frequency of the signal sampling by the A/D converter 1 is equal to 96 kHz. During the sixth mode of operation, the switches 4B and 4C select the DVD encoding circuit 6. In this case, the DVD encoding circuit 6 generates a sequence of a header signal and a user data block (a packet or packets) in response to the second digital audio signal for every pack. The user data block (the pack or packets) contains the second digital audio signal. During the sixth mode of operation, a 1-pack-corresponding segment of the composite digital audio signal generated by the DVD encoding circuit 6 has a form such as shown in FIG. 4. The user data block has 2,034 bytes.

The apparatus output terminal 4D can be connected to a transmission line in, for example, a communication network. In this case, the output signal of the CD-ROM encoding circuit 4A or the DVD encoding circuit 6 can be fed to the transmission line before being transmitted therealong.

The apparatus output terminal 4D can be connected to a pre-mastering apparatus or a mastering apparatus for a CD-ROM or a DVD. In this case, the output signal of the CD-ROM encoding circuit 4A or the DVD encoding circuit 6 can be fed to the pre-mastering apparatus or the mastering apparatus before being recorded thereby on a pre-master disc or a master disc for a CD-ROM or a DVD.

The apparatus output terminal 4D can be connected to a recording apparatus. In this case, the output signal of the CD-ROM encoding circuit 4A or the DVD encoding circuit 6 can be fed to the recording apparatus before being recorded thereby on a recording medium such as a magnetic tape or a magnetic disc.

FIG. 5 shows a drive apparatus 8 for a CD-WO 9. The drive apparatus 8 can be connected to the output terminal 5A in FIG. 1. In this case, the output signal of the CD encoding circuit 5 can be fed to the drive apparatus 8 before being recorded thereby on the CD-WO 9.

Second Embodiment

FIG. 6 shows a second embodiment of this invention which is similar to the embodiment of FIGS. 1-5 except for the following design change. The embodiment of FIG. 6 uses a signal processing circuit 2A instead of the signal processing circuit 2 in FIG. 1.

An analog audio signal inputted to the A/D converter 1 is composed of 2-channel signals. The input analog audio signal may be composed of 4-channel signals, or 6-channel signals.

The signal processing circuit 2A includes a DSP (digital signal processor), a microcomputer, or a similar device having a combination of an input/output port, a processing section, a ROM, and a RAM. The signal processing circuit 2A operates in accordance with a program stored in the ROM.

The signal processing circuit 2A receives the first digital audio signal from the A/D converter 1. The signal processing circuit 2A is programmed to process the first digital audio signal into a second digital audio signal according to a predetermined signal-compression technique including an orthogonal transform process. The predetermined signal-compression technique may also include a Huffman encoding process. In this case, the orthogonal transform process may be omitted from the predetermined signal-compression technique. The signal processing by the signal processing circuit 2A is implemented block by block. Here, "block" corresponds to a predetermined number "2.sup.m" of data pieces of the first digital audio signal per channel.

Specifically, the signal processing circuit 2A subjects a set of 2.sup.m data pieces of the first digital audio signal to orthogonal transform, thereby generating a signal representing the frequency spectrum of the first digital audio signal. The signal processing circuit 2A divides the resultant frequency-spectrum signal into signals in different frequency bands by a filtering process. The signal processing circuit 2A normalizes and quantizes each of the frequency-band signals. The signal processing circuit 2A generates helper information representing the conditions of the normalization (for example, the normalization level or the normalization bit number) and the conditions of the quantization. The signal processing circuit 2A combines the normalization/quantization-resultant signals and the helper information. The signal processing circuit 2A subjects the combination-resultant signal to an allocation process. The signal processing circuit 2A outputs the allocation-resultant signal to the switch 4B.

The signal processing circuit 2A may subject the combination-resultant signal to a Huffman encoding process. In this case, the signal processing circuit 2A subjects the encoding-resultant signal to an allocation process. The signal processing circuit 2A outputs the allocation-resultant signal to the switch 4B.

Third Embodiment

FIG. 7 shows a third embodiment of this invention which is similar to the embodiment of FIGS. 1-5 except for the following design change. The embodiment of FIG. 7 uses a signal processing circuit 2B instead of the signal processing circuit 2 in FIG. 1.

The signal processing circuit 2B includes a DSP (digital signal processor), a microcomputer, or a similar device having a combination of an input/output port, a processing section, a ROM, and a RAM. The signal processing circuit 2B operates in accordance with a program stored in the ROM.

The signal processing circuit 2B receives the first digital audio signal from the A/D converter 1. The signal processing circuit 2B is programmed to process the first digital audio signal into a second digital audio signal according to a predetermined signal-compression technique.

FIG. 8 shows a flow of operation of the signal processing circuit 2B. It should be noted that FIG. 8 does not show the hardware structure of the signal processing circuit 2B. With reference to FIG. 8, a block 22 subjects an input signal (that is, the first digital audio signal from the A/D converter 1) to a windowing process and an orthogonal transform process. Preferably, the orthogonal transform process is of the MDCT (modified discrete cosine transform) type. The resultant data representing orthogonal transform coefficients are divided by the block 22 into coefficient-representing data pieces corresponding to different frequency bands respectively.

A block 23 following the block 22 decides scale factors for the coefficient-representing data pieces corresponding to the frequency bands respectively. The block 23 normalizes the coefficient-representing data pieces in response to the decided scale factors respectively. The block 23 informs a block 27 of the decided scale factors.

A block 24 following the block 23 quantizes the normalization-resultant data pieces in response to variable quantization factors (variable quantization steps). The bock 24 may implement the quantization-resultant data pieces to entropy encoding.

A block 25 following the block 23 calculates desired code amounts (desired bit numbers) from the normalization-resultant data pieces for the frequency bands respectively. The minimum audible limit characteristics and the masking effects of a predetermined auditory sensation model are used in calculating the desired code amounts.

A block 26 following the block 25 calculates desired quantization factors (desired quantization steps) from the desired code amounts for the frequency bands respectively. The block 26 informs the block 24 of the desired quantization factors (the desired quantization steps). The block 24 quantizes the normalization-resultant data pieces in response to quantization factors equal to the desired quantization factors. The block 26 informs the block 27 of the desired quantization factors as actual quantization factors used by the block 24.

The block 27 follows the block 24. The block 27 generates helper information such as header information. The block 27 combines the quantization-resultant data pieces, the information of the scale factors, the information of the quantization factors, and the helper information into a bit stream which is an output signal of the signal processing circuit 2B.

FIG. 9 is a flowchart of a segment of the program which corresponds to the blocks 24, 25, and 26 in FIG. 8. Signal processing by the blocks 24, 25, and 26 is implemented frame by frame. Here, "frame" is a predetermined time interval. As shown in FIG. 9, a first step S1 of the program segment decides first quantization bit numbers (first quantization factors) for the frequency bands respectively. Regarding the normalization-resultant data pieces, the step S1 estimates generated bit numbers in response to the decided first quantization bit numbers for the frequency bands respectively. The step S1 calculates a total bit number which equals the sum of the estimated bit numbers.

A step S2 following the step S1 calculates an available bit number in the current frame. A step S3 following the step S2 compares the calculated total bit number and the calculated available bit number to decide whether or not a code amount is insufficient. When the total bit number is greater than the available bit number, that is, when a code amount is insufficient, the program advances from the step S3 to a step S4. Otherwise, the program advances from the step S3 to a step S8.

The step S4 calculates band powers p[i] which are equal to the square of the scale factors for the frequency bands respectively.

Here, "i" denotes a variable integer for identifying the frequency bands. The step S4 calculates masking curves m[i] from the calculated band powers p[i] in accordance with the minimum audible limit characteristic and the masking effects of a predetermined auditory sensation model. Specifically, the masking curves m[i] are given by the convolution of model-based reference curves r[i] and the band powers p[i].

A step S5 following the step S4 calculates standard noise levels N[i] from the minimum audible limits abs[i] and the masking curves m[i] for the frequency bands respectively. For example, the calculation of the standard noise levels N[i] uses an equation given as: N[i]=max[m[i], abs[i]] where "max" denotes an operator for selecting the greater of the values in the brackets.

A step S6 subsequent to the step S5 distributes deleted bits (that is, bits to be deleted) to the frequency bands according to the following rules. First one of the deleted bits is allocated to the frequency band having the highest standard noise level. Then, the standard noise level corresponding to this frequency band is reduced by a predetermined level. Subsequently, second one of the deleted bits is allocated to the frequency band having the highest standard noise level. Then, the standard noise level corresponding to this frequency band is reduced by the predetermined level. These processes are iteratively executed until a final one of the deleted bits is allocated.

In other words, first one of the deleted bits is allocated to the frequency band having the highest standard noise level. Second one of the deleted bits is allocated to the frequency band having the second highest standard noise level. Third one of the deleted bits is allocated to the frequency band having the third highest standard noise level. These processes are iteratively executed until a final one of the deleted bits is allocated. During these processes, when one of the deleted bits is allocated to a frequency band, the standard noise level corresponding to this frequency band is decreased by a predetermined level.

Generally, the shape of the distribution of the deleted bits is similar to the shape formed by the standard noise levels N[i]. The block S6 corrects the first quantization bit numbers (the first quantization factors) into second quantization bit numbers (second quantization factors) in response to the distribution of the deleted bits to the frequency bands respectively. After the step S6, the program advances to a step S7.

The step S8 allocates surplus bits to the frequency bands. The step S8 sets second quantization bit numbers (second quantization factors) equal to the first quantization bit numbers (the first quantization factors) for the frequency bands respectively. After the step S8, the program advances to the step S7.

The step S7 quantizes the normalization-resultant data pieces in response to the second quantization factors (the second quantization bit numbers) of the frequency bands respectively. After the step S7, the current execution cycle of the program segment ends.

As shown in FIG. 10, the standard noise level varies frequency-band to frequency-band even in the case where the noise level of the original signal is fixed independent of the frequency bands. The stepwise line formed by the standard noise levels is shaped according to the auditory sensation model. The deleted bits are distributed to the frequency bands according to the standard noise levels. Therefore, it is possible to effectively suppress a decrease in tone quality in auditory sensation which would be caused by the quantization.

Fourth Embodiment

FIG. 11 shows a fourth embodiment of this invention which is similar to the embodiment of FIGS. 7-10 except for design changes indicated hereinafter. The embodiment of FIG. 11 uses a signal processing circuit 2C instead of the signal processing circuit 2B in FIG. 7.

The signal processing circuit 2C includes a DSP (digital signal processor), a microcomputer, or a similar device having a combination of an input/output port, a processing section, a ROM, and a RAM. The signal processing circuit 2C operates in accordance with a program stored in the ROM.

The signal processing circuit 2C receives the first digital audio signal from the A/D converter 1. The signal processing circuit 2C is programmed to process the first digital audio signal into a second digital audio signal according to a predetermined signal-compression technique.

FIG. 12 is a flowchart of a segment of the program in the signal processing circuit 2C. Generally, the program segment in FIG. 12 is iteratively executed. As shown in FIG. 12, a first step S11 of the program segment fetches information of used code amounts in all time intervals composing an object term. For example, the object term corresponds to the time length of a tune represented by an input audio signal or the sum of the time lengths of all tunes for one disc. The step S11 calculates a mean code amount Tm among the used code amounts. The step S11 fetches information of a desired code amount Td.

A step S12 following the step S11 compares the mean code amount Tm and the desired code amount Td to decide whether an insufficient condition or a surplus condition occurs in code amount. When the mean code amount Tm is greater than the desired code amount Td, that is, when a surplus condition occurs, the program advances from the step S12 to a step S13. Otherwise, the program advances from the step S12 to a step S19.

The step S13 calculates the deviation (the difference) .DELTA. which is equal to the used code amount minus the desired code amount Td for each of the time intervals. The step S13 quantizes the deviation-.DELTA.-representing data piece in response to a predetermined quantization step width (a predetermined quantization step size) St for each of the time intervals. The quantization step width (the quantization step size) St is expressed in bit number. The step S13 generates a histogram related to the deviations .DELTA..

A step S14 following the step S13 calculates the deviation sum Sm in negative ranges of the histogram and the deviation sum Sp in positive ranges of the histogram according to equations given as:

.times..function. ##EQU00001## .times..function. ##EQU00001.2## where "i" denotes an index of the histogram, and "min" and "max" denote an index minimum limit and an index maximum limit respectively.

A step S15 subsequent to the step S14 calculates the ratio "Sm/(Sm+Sp)". The step S15 compares the calculated ratio with a predetermined value Bd equal to, for example, 0.33. When the calculated ratio is equal to or greater than the predetermined value Bd, the program advances from the step 315 to a step S16. Otherwise, the program advances from the step S15 to a step S17.

The step S16 sets an offset value Ofs of the histogram to "0".

After the step S16, the program advances to a step S18.

The step S17 sets the offset value Ofs so that the ratio "Sm/(Sm+Sp)" will be equal to or greater than the predetermined value Bd. After the step S17, the program advances to the step S18.

For each of the time intervals, the step S18 compares the deviation .DELTA. with the product of the offset value Ofs and the quantization step width St. When the deviation .DELTA. is equal to or smaller than the product "OfsSt", the step S18 calculates a code amount adjustment value (a code amount corrective value) Adj from the offset value Ofs and the quantization step width St according to the following equation. Adj=-OfsSt When the deviation .DELTA. is greater than the product "OfsSt", the step S18 calculates the code amount adjustment value (the code amount corrective value) Adj according to the following equation. Adj=-OfsSt-{(Sp-Sm)/Sp}(.DELTA.-OfsSt) The step S18 calculates the code amount adjustment value (the code amount corrective value) Adj for each of the time intervals. After the step S18, the current execution cycle of the program segment ends.

For each of the time intervals, the step S19 calculates the code amount adjustment value (the code amount corrective value) Adj from the mean code amount Tm and the desired code amount Td according to the following equation. Adj=Td-Tm After the step S19, the current execution cycle of the program segment ends.

With reference to FIG. 13, the code amount adjustment value (the code amount corrective value) Adj varies as a function of the deviation .DELTA.. Specifically, in a range where the deviation .DELTA. is positive, the code amount adjustment value (the code amount corrective value) Adj increases as the deviation .DELTA. increases.

FIG. 14 is a flowchart of another segment of the program in the signal processing circuit 2C. The program segment in FIG. 14 is executed frame by frame. As shown in FIG. 14, a first step S21 of the program segment decides first quantization bit numbers (first quantization factors) for the frequency bands respectively. Regarding the normalization-resultant data pieces, the step S21 estimates generated bit numbers in response to the decided first quantization bit numbers for the frequency bands respectively. The step S21 calculates a total bit number which equals the sum of the estimated bit numbers.

A step S22 following the step S21 fetches information of the code amount adjustment value (the code amount corrective value) Adj for the current frame.

A step S23 subsequent to the step S22 decides whether or not the code amount adjustment value (the code amount corrective value) Adj is negative. When the code amount adjustment value (the code amount corrective value) Adj is negative, the program advances from the step S23 to a step S24. Otherwise, the program advances from the step S23 to a step S28.

The step S24 calculates band powers p[i] which are equal to the square of the scale factors for the frequency bands respectively. Here, "i" denotes a variable integer for identifying the frequency bands. The step S24 calculates masking curves m[i] from the calculated band powers p[i] in accordance with the minimum audible limit characteristic and the masking effects of a predetermined auditory sensation model. Specifically, the masking curves m[i] are given by the convolution of model-based reference curves r[i] and the band powers p[i].

A step S25 following the step S24 calculates standard noise levels N[i] from the minimum audible limits abs[i] and the masking curves m[i] for the frequency bands respectively. For example, the calculation of the standard noise levels N[i] uses an equation given as: N[i]=max[m[i], abs[i]] where "max" denotes an operator for selecting the greater of the values in the brackets.

A step S26 subsequent to the step S25 distributes deleted bits (that is, bits to be deleted) to the frequency bands according to the following rules. First one of the deleted bits is allocated to the frequency band having the highest standard noise level. Then, the standard noise level corresponding to this frequency band is reduced by a predetermined level. Subsequently, second one of the deleted bits is allocated to the frequency band having the highest standard noise level. Then, the standard noise level corresponding to this frequency band is reduced by the predetermined level. These processes are iteratively executed until a final one of the deleted bits is allocated.

In other words, first one of the deleted bits is allocated to the frequency band having the highest standard noise level. Second one of the deleted bits is allocated to the frequency band having the second highest standard noise level. Third one of the deleted bits is allocated to the frequency band having the third highest standard noise level. These processes are iteratively executed until a final one of the deleted bits is allocated. During these processes, when one of the deleted bits is allocated to a frequency band, the standard noise level corresponding to this frequency band is decreased by a predetermined level.

Generally, the shape of the distribution of the deleted bits is similar to the shape formed by the standard noise levels N[i]. The block S26 corrects the first quantization bit numbers (the first quantization factors) into second quantization bit numbers (second quantization factors) in response to the distribution of the deleted bits to the frequency bands respectively. After the step S26, the program advances to a step S27.

The step S28 allocates surplus bits to the frequency bands. The step S28 sets second quantization bit numbers (second quantization factors) equal to the first quantization bit numbers (the first quantization factors) for the frequency bands respectively. After the step S28, the program advances to the step S27.