JP3064522B2 - Signal processing method and compressed data recording / reproducing device - Google Patents

Abstract

PURPOSE:To reduce recording data quantity onto an IC card without deteriorating sound quality by eliminating part of bit compressed data not sensed audibly and to attain high speed dubbing. CONSTITUTION:ATC audio data obtained from compression processing by an adaptive conversion coding (ATC) encoder 63 are fed to a residue bit reduction circuit device 84 being one type of variable bit rate coder via, e.g. a RAM 85, in which bit reduction giving noise less than a masking threshold level is implemented. That is, compression coding data with a prescribed bit rate recorded on a magneto-optical disk 1 are reproduced and the result is fed to the residue bit reduction circuit device 84 without implementing compression decoding processing, in which bit parts giving a quantization noise level not sensed audibly is processed in such a way that it is eliminated in a form of a sample subject to bit compression processing in small blocks divided minutely as to time and frequency and the result is recorded on an IC card 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing method for compressing bits of a digital audio signal or the like and a compressed data recording / reproducing apparatus, and more particularly to a method for recording data between a constant bit rate recording medium and a variable bit rate recording medium. And a compressed data recording and reproducing apparatus.

[0002]

2. Description of the Related Art The applicant of the present invention has previously disclosed a technique for compressing an input digital audio signal into bits and recording the digital audio signal in bursts using a predetermined data amount as a recording unit, for example, as disclosed in Japanese Patent Application No. 2-221364. , Japanese Patent Application No. 2-2136
No. 5, Japanese Patent Application No. 2-222821, Japanese Patent Application No. 2-2228
No. 23 has been proposed in the specification and drawings.

This technology uses a magneto-optical disk as a recording medium and records and reproduces AD (adaptive difference) PCM audio data defined in an audio data format of a so-called CD-I (CD-interactive) or CD-ROM XA. The ADPCM data is recorded in a burst on the magneto-optical disk using, for example, 32 sectors of ADPCM data and several sectors for linking for interleave processing as a recording unit.

Several modes can be selected for the ADPCM audio in the recording / reproducing apparatus using this magneto-optical disk. For example, a level A having a compression ratio twice as high as the normal CD reproducing time can be selected. , 4x level B,
An eight-fold level C is defined. That is, for example, in the case of the level B, the digital audio data is compressed to approximately 1/4, and the reproduction time (play time) of the disc recorded in this level B mode is a standard CD format (CD). -DA format). This is the standard 12c for smaller discs
Since the same recording and reproduction time as m can be obtained, the size of the apparatus can be reduced.

However, the rotation speed of the disk is a standard C
Since it is the same as D, for example, in the case of the level B, compressed data for a reproduction time four times as long as the predetermined time is obtained. For this reason, for example, the same compressed data is read out four times in units of time such as sectors or clusters, and only one of the compressed data is used for audio reproduction. Specifically, when scanning (tracking) a spiral recording track, 1
A track jump is performed to return to the original track position for each rotation, and the reproduction operation proceeds in such a form that the same track is repeatedly tracked four times. This means that normal compressed data need only be obtained at least once out of, for example, four times of redundant reading, and is resistant to errors due to disturbances and the like, and is particularly preferable when applied to portable small devices.

In the future, it is considered that a semiconductor memory is used as a recording medium. In order to further increase the compression efficiency, compression encoding using a variable bit rate such as so-called entropy encoding is used. Specifically, it is a method of recording and reproducing an audio signal using a so-called IC card.
Record and reproduce compressed data that has been bit-compressed at a variable bit rate.

[0007] In such an IC card using a semiconductor memory, an increase in recording capacity and a reduction in price have been realized with the progress of semiconductor technology. The capacity is likely to be short and expensive. Therefore, it is sufficiently conceivable that the content is transferred from another inexpensive and large-capacity recording medium such as the above-mentioned magneto-optical disk to an IC card or the like and frequently rewritten and used. Specifically, for example, of a plurality of songs recorded on the magneto-optical disk, a desired song is dubbed to an IC card, and when unnecessary, another song is replaced. In this manner, by frequently rewriting the contents of the IC card, various songs can be enjoyed outdoors or the like with a small number of IC cards.

[0008]

By the way, for example, the music recorded on the magneto-optical disk is reproduced and the IC is read.
When dubbing to a card, the price per unit bit of an IC card is much higher than the price per unit bit of a magneto-optical disk. Therefore, when dubbing to the IC card, it is desirable to further compress the information in addition to the high-efficiency encoding on the magneto-optical disk.

Also, for example, in the case where some of the plurality of songs recorded on the magneto-optical disk are to be dubbed to the IC card, in addition to the high-efficiency code on the magneto-optical disk, When information is further compressed, the bit rate changes according to the contents, and the data amount may be different even for the same reproduction time, so that the data amount in the magneto-optical disk and the data amount in the IC card are different. It can be different. For this reason, the number of songs that can be recorded on the IC card, the optimum combination of songs, and the like cannot be immediately known before recording, so that only the middle of the song can be recorded or the surplus portion cannot be used effectively. Sometimes.

In performing such dubbing, if compressed data from the magneto-optical disk is decoded and returned to the original reproduction time, the data is encoded with a high-efficiency code at a variable bit rate and recorded on an IC card. However, it takes only the same time as the normal reproduction (actual playing time), and higher-speed dubbing is desired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has been used when data recorded by bit compression processing at a fixed bit rate is compressed at a fixed or variable bit rate and written to an IC card or the like. Then, the auditory redundant information portion is reduced in a sample state in a small block subdivided with respect to time and frequency to reduce the amount of information, and furthermore, a masking threshold that is acoustically desirable is reduced. An object of the present invention is to provide a signal processing method and a compressed data recording / reproducing apparatus which can write data into an IC card or the like at a given variable bit rate, instantaneously check the amount of writable data at the time of writing, and enable high-speed writing. I do.

[0012]

A signal processing method according to the present invention is a signal processing method for further compressing a bit-compressed signal at a constant bit rate. By using a high-efficiency code for quantizing the sample, at least a part of the bits giving a quantization noise level that is inaudible from the signal that has been bit-compressed at the constant bit rate is subdivided in time and frequency. The above problem is solved by removing in the form of bit-compressed samples in small blocks.

Further, the compressed data recording / reproducing apparatus according to the present invention is a compressed data recording / reproducing apparatus having a compressed data recording system for further compressing a bit-compressed signal at a constant bit rate and recording the signal on a recording medium. From the bit-compressed signal at the constant bit rate, at least some of the bits that provide an inaudible quantization noise level are extracted from the bit-compressed samples in small blocks that are subdivided in time and frequency. The above-mentioned problem is solved by removing the data in the form, performing bit compression processing at a variable bit rate, and recording the data on the recording medium.

Here, the quantization noise level that cannot be heard audibly includes, for example, a quantization noise level lower than an allowable noise level determined by a masking threshold and a minimum audibility.

Further, a compressed data recording / reproducing apparatus according to the present invention comprises: a compressed data reproducing system for reproducing at least digital data from one recording medium which has been bit-compressed at a constant bit rate and recorded; A compressed data recording system for recording at least digital data on another recording medium on which bit compression processing is performed and recording the compressed data recorded on one recording medium of the reproduction system. The above-mentioned problem is solved by reducing the number of bits giving a quantization noise level lower than the threshold, sending the bit to the recording system, and recording the data on the other recording medium.

At this time, the bit which gives the quantization noise level lower than the masking threshold without deleting the compressed data as it is without being expanded is sent to the above-mentioned recording system, and fixed or variable bit rate is fixed to the other recording medium. Recording with bit compression is desirable in order to reduce the hardware scale and increase the compression ratio.

Here, not only the data which has been subjected to the bit compression processing at the constant bit rate but also the constant recording rate data which has been bit-compressed to the other recording medium at a variable bit rate are stored in the one recording medium. Is preferably recorded. It is preferable that not only the variable bit rate compressed data but also data amount information for performing bit compression recording at a constant bit rate on the one recording medium is recorded on the other recording medium.

[0018]

The compressed data recorded on the one recording medium is sent to the recording system of the other recording medium after reducing the number of bits giving a quantization noise level lower than the masking threshold and then transmitting the compressed data to the recording system of the other recording medium. Data transfer can be performed. Also, by looking at the data amount information at the time of variable bit rate compression recorded on the one recording medium, the data capacity necessary for recording on the other recording medium can be quickly confirmed, and the recordable music You can easily know the optimal combination of numbers and songs. This is the same in the opposite case, that is, when recording from the other recording medium to the one recording medium.

[0019]

FIG. 1 is a block circuit diagram showing a schematic configuration of an embodiment of a compressed data recording / reproducing apparatus to which a signal processing method according to the present invention is applied. The recording / reproducing apparatus of FIG.
The recording / reproducing unit of the magneto-optical disk 1 as one recording medium and the recording unit of the IC card 2 as another recording medium are assembled in one system. When the signal reproduced by the reproducing system on the magneto-optical disk recording / reproducing unit side is recorded by the IC card recording unit, the signal is read from the magneto-optical disk 1 of the reproducing system by the optical head 53 and transmitted to the decoder 71. E
Reproduced compressed data that has been subjected to FM demodulation, deinterleave processing, error correction processing, etc., specifically, for example, ATC (Adap
tive Transform Coding) The audio data is sent to the memory 85 of the IC card recording unit, and the memory 85 is subjected to a variable bit rate encoding process by a surplus bit reduction circuit 84, and the IC card interface circuit The data is recorded on the IC card 2 via the IC card 86. Thus, the reproduced compressed data is sent to the recording system in a compressed state before being subjected to the decompression process by the ATC decoder 73 which performs the reverse process of the ATC, for example.
The variable bit rate is encoded and recorded on the IC card 2. Here, various IC memories such as an IC memory cartridge and an IC memory pack may be used instead of the IC card.

By the way, during normal reproduction (for audio listening), a predetermined data amount unit (for example, 3
Compressed data is read out in (2 sectors + several sectors), expanded and converted into a continuous audio signal. At the time of the so-called dubbing, the compressed data on the medium is continuously read and sent to the recording system. Have recorded. Thereby, high-speed (short-time) dubbing according to the data compression ratio can be performed.

Hereinafter, the specific configuration of FIG. 1 will be described in detail. In the magneto-optical disk recording / reproducing unit of the compressed data recording / reproducing apparatus shown in FIG. 1, a magneto-optical disk 1 driven by a spindle motor 51 is used as a recording medium. When recording data on the magneto-optical disk 1, for example, a so-called magnetic field modulation recording is performed by applying a modulation magnetic field corresponding to the recording data with the magnetic head 54 while irradiating the laser light with the optical head 53. The data is recorded along the recording track of. At the time of reproduction, a recording track of the magneto-optical disk 1 is traced by a laser beam by the optical head 53, and reproduction is performed magneto-optically.

The optical head 53 includes, for example, a laser light source such as a laser diode, a collimator lens, an objective lens,
The optical system includes optical components such as a polarizing beam splitter and a cylindrical lens, and a photodetector having a light receiving portion having a predetermined pattern. The optical head 53 is provided at a position facing the magnetic head 54 via the magneto-optical disk 1. When data is recorded on the magneto-optical disk 1, the magnetic head 54 is driven by a recording-system head drive circuit 66, which will be described later, to apply a modulation magnetic field in accordance with the recorded data. By irradiating the track with laser light, thermomagnetic recording is performed by a magnetic field modulation method. The optical head 53 detects reflected light of the laser beam applied to the target track, detects a focus error by, for example, a so-called astigmatism method, and detects a tracking error by, for example, a so-called push-pull method. When reproducing data from the magneto-optical disk 1, the optical head 53 detects the focus error and the tracking error, and at the same time, detects the difference in the polarization angle (Kerr rotation angle) of the reflected light of the laser light from the target track and reproduces the data. Generate a signal.

The output of the optical head 53 is supplied to an RF circuit 55. The RF circuit 55 extracts the focus error signal and the tracking error signal from the output of the optical head 53 and supplies the focus error signal and the tracking error signal to the servo control circuit 56.
Feed to 1.

The servo control circuit 56 comprises, for example, a focus servo control circuit, a tracking servo control circuit, a spindle motor servo control circuit, a thread servo control circuit and the like. The focus servo control circuit performs focus control of the optical system of the optical head 53 so that the focus error signal becomes zero. Further, the tracking servo control circuit performs tracking control of the optical system of the optical head 53 so that the tracking error signal becomes zero. Further, the spindle motor servo control circuit controls the spindle motor 51 so as to rotate the magneto-optical disk 1 at a predetermined rotation speed (for example, a constant linear speed). The thread servo control circuit moves the optical head 53 and the magnetic head 54 to target track positions of the magneto-optical disk 1 specified by the system controller 57. The servo control circuit 56 that performs such various control operations sends information indicating the operation state of each unit controlled by the servo control circuit 56 to the system controller 57.

A key input operation unit 58 and a display unit 59 are connected to the system controller 57. The system controller 57 controls a recording system and a reproduction system in an operation mode specified by operation input information from the key input operation unit 58. Further, the system controller 7 controls the optical head 53 and the magnetic head 54 based on the address information in the unit of sector reproduced from the recording track of the magneto-optical disk 1 based on the header time and the Q data of the subcode.
Manages a recording position and a reproduction position on the recording track that are being traced. Further, the system controller 57
The bit compression mode information in the ATC encoder 63, which will be described later, which is switched and selected by the key input operation unit 58,
Based on the bit compression mode information in the reproduction data obtained from the F circuit 55 through a reproduction system described later, the bit compression mode is displayed on the display unit 59, and the data compression ratio in the bit compression mode and the recording track are recorded. Control is performed to display the reproduction time on the display unit 59 based on the above reproduction position information.

This reproduction time display is based on address information (absolute time information) in sector units reproduced from a recording track of the magneto-optical disk 1 by a so-called header time or so-called subcode Q data, etc. The actual time information is obtained by multiplying the reciprocal of the compression ratio (for example, 4 in the case of 、 compression), and this is displayed on the display unit 9. At the time of recording, if absolute time information is recorded in advance on a recording track of a magneto-optical disk or the like (preformatted), the preformatted absolute time information is read and the data compression ratio is adjusted. By multiplying the reciprocal, the current position can be displayed by the actual recording time.

Next, in the recording system of the recording / reproducing apparatus of the disc recording / reproducing apparatus, the analog audio input signal A _IN from the input terminal 60 is supplied to the A through the low-pass filter 61.
The A / D converter 62 quantizes the analog audio input signal A _IN . A /
The digital audio signal obtained from the D converter 62 is supplied to the ATC encoder 63. The digital audio input signal D _IN from the input terminal 67 is supplied to the ATC encoder 63 via the digital input interface circuit 68. The ATC encoder 63 is
The digital audio PCM data of a predetermined transfer rate obtained by quantizing the input signal A _IN by the A / D converter 62 is subjected to bit compression (data compression) processing corresponding to various modes in the CD-I system described above. ,
The operation mode is designated by the system controller 57. For example, in the predetermined mode, the sampling frequency is 44.1 kHz and the average number of bits per sample is 4 bits of compressed data.
Consider the mode supplied to 4. The data transfer rate in this predetermined mode is 1/4 (18.7) of the data transfer rate (75 sectors / second) of the standard CD-DA format.
5 sectors / second).

Here, in the embodiment of FIG. 1, the sampling frequency of the A / D converter 62 is, for example, the standard C
4 which is the sampling frequency of the D-DA format
It is fixed at 4.1 kHz, and it is assumed that the ATC encoder 13 performs bit compression processing from 16 bits to 4 bits after performing a sampling rate conversion according to the compression mode, for example. doing.
As another configuration example, the sampling frequency of the A / D converter 12 may be switched and controlled according to the compression mode. In this case, the switched A / D is controlled.
The cutoff frequency of the low-pass filter 61 is also switched according to the sampling frequency of the converter 12. That is, the sampling frequency of the A / D converter 62 and the cutoff frequency of the low-pass filter 61 may be simultaneously switched in accordance with the compression mode. Also, even if the sampling frequency does not change depending on the mode,
In a mode in which the number of bits used is small, the restriction on the frequency band may be increased.

Next, writing and reading of data in the memory 64 are controlled by the system controller 57.
ATC data supplied from the ATC encoder 63 is temporarily stored, and is used as a buffer memory for recording on a disk as needed. That is, for example, in the above-described predetermined mode, the compressed audio data supplied from the ATC encoder 63 has a data transfer rate of 1/4 of the data transfer rate (75 sectors / second) of the standard CD-DA format, that is, 1
This is reduced to 8.75 sectors / sec, and the compressed data is continuously written to the memory 14. The compressed data (ATC data) is one for every four sectors as described above.
Sector recording is sufficient, but such recording at every fourth sector is practically impossible. Therefore, continuous recording of sectors as described later is performed. In this recording, a data transfer rate (7), which is the same as the standard CD-DA format, is used as a recording unit in a cluster consisting of a predetermined plurality of sectors (for example, 32 sectors + several sectors) through a pause period.
(5 sectors / sec). That is, in the memory 64, 1 is set according to the bit compression rate.
The ATC audio data of the predetermined mode written continuously at a low transfer rate of 8.75 (= 75/4) sectors / second is read as recording data in a burst at the transfer rate of 75 sectors / second. The overall data transfer speed of the read and recorded data, including the recording pause period, is as low as 18.75 sectors / sec. The instantaneous data transfer rate in the above is the standard 75 sectors / second. Therefore, when the disk rotation speed is the same speed (constant linear speed) as the standard CD-DA format, the same recording density and storage pattern as in the CD-DA format are recorded.

The ATC audio data, ie, recorded data, read from the memory 64 in a burst at the (instantaneous) transfer rate of 75 sectors / second is transferred to the encoder 65.
Supplied to Here, from the memory 64 to the encoder 65
In the data sequence supplied to the cluster, the unit continuously recorded in one recording is a cluster including a plurality of sectors (for example, 32 sectors) and several sectors for cluster connection arranged before and after the cluster. The cluster connection sector is set to be longer than the interleave length in the encoder 65, so that even if interleaved, data in other clusters is not affected.

The encoder 65 operates on the recording data supplied in bursts from the memory 64 as described above.
Encoding processing (parity addition and interleaving processing) for error correction, EFM encoding processing, and the like are performed. The recording data that has been subjected to the encoding process by the encoder 65 is supplied to the magnetic head drive circuit 66. The magnetic head drive circuit 66 is connected to the magnetic head 54 and drives the magnetic head 54 so as to apply a modulation magnetic field according to the recording data to the magneto-optical disk 1.

The system controller 57 controls the memory 64 as described above,
By this memory control, the recording position is controlled so that the recording data read out from the memory 64 in a burst manner is continuously recorded on the recording track of the magneto-optical disk 2.
The recording position is controlled by controlling the recording position of the recording data read in a burst from the memory 64 by the system controller 57 and transmitting a control signal designating the recording position on the recording track of the magneto-optical disk 1 to a servo control circuit. 56.

Next, the reproducing system of the magneto-optical disk recording / reproducing unit will be described. This reproducing system is for reproducing the recorded data continuously recorded on the recording tracks of the magneto-optical disk 1 by the recording system described above.
A decoder 71 is provided, in which a reproduction output obtained by tracing a recording track of the magneto-optical disk 1 with a laser beam by the optical head 53 is binarized by the RF circuit 55 and supplied.

The decoder 71 corresponds to the encoder 65 in the above-described recording system, and performs the above-described decoding processing for error correction and EFM decoding on the reproduced output binarized by the RF circuit 55. ATC audio data of the above-mentioned predetermined mode is performed by performing processing such as processing.
Reproduction is performed at a transfer rate of 75 sectors / sec, which is faster than the normal transfer rate in the predetermined mode. The reproduction data obtained by the decoder 71 is supplied to the memory 72.

In the memory 72, data writing and reading are controlled by the system controller 57, and reproduced data supplied from the decoder 71 at a transfer rate of 75 sectors / second is written in burst at the transfer rate of 75 sectors / second. It is. The memory 72 stores the reproduced data written in a burst at the transfer rate of 75 sectors / sec.
It is read continuously at a transfer rate of seconds.

The system controller 57 writes the reproduced data to the memory 72 at a transfer rate of 75 sectors / sec.
Memory control is performed such that data is read continuously at a transfer rate of 5 sectors / second. Further, the system controller 57 performs the above-described memory control for the memory 72, and reproduces the reproduction data written in a burst from the memory 72 by the memory control from the recording track of the magneto-optical disk 1 continuously. Control the playback position. This playback position control is performed by the system controller 5.
7 controls the reproduction position of the reproduction data read out from the memory 72 in a burst manner, and supplies a servo control circuit 56 with a control signal designating the reproduction position on the recording track of the magneto-optical disk 1.

The ATC audio data in the predetermined mode as the reproduction data continuously read from the memory 72 at a transfer rate of 18.75 sectors / second is supplied to the ATC decoder 73. The ATC decoder 73 corresponds to the ATC encoder 63 of the recording system. When the operation mode is specified by the system controller 57, the ATC decoder 73 expands the 4-bit ATC data by four times (bit expansion). Play 16-bit digital audio data. The digital audio data from the ATC decoder 73 is supplied to a D / A converter 74.

The D / A converter 74 includes an ATC decoder 73
Is converted into an analog signal to form an analog audio output signal A _OUT . The analog audio signal A _OUT obtained by the D / A converter 74 is output from an output terminal 76 via a low-pass filter 75.

Next, the analog audio input signal A _IN from the input terminal 60 is supplied to an A / D converter 62 via a low-pass filter 61 and quantized.
The digital audio signal obtained by being encoded by the C encoder 63 can be further compressed (bit-compressed) and recorded on the IC card 2. Hereinafter, this IC card recording system will be described.

That is, ATC audio data obtained by compression processing by the ATC encoder 63 is, for example, R
The signal is sent to a surplus bit reduction circuit 84, which is a kind of variable bit rate encoder, through the AM 85. In the surplus bit reduction circuit 84, a bit that gives a noise lower than a masking threshold is output. Is reduced. This process is executed while reading and writing data from and to the memory 85. The variable bit rate compression encoded data from the surplus bit reduction circuit 84 is recorded on the IC card 2 via the IC card interface circuit 86.

Here, compressed data (ATC) from the decoder 71 of the reproducing system of the magneto-optical disk recording / reproducing unit is used.
) Is sent to the memory 85 of the IC card recording unit without being expanded. This data transfer is performed by the system controller 57 controlling the memory 85 and the like during so-called high-speed dubbing. The compressed data from the memory 72 may be sent to the memory 85.

Next, a so-called high-speed digital dubbing operation will be described. First, at the time of so-called high-speed digital dubbing, the system controller 7 performs a predetermined high-speed dubbing control processing operation by operating a dubbing operation key or the like of the key input operation unit 8. In particular,
The compressed data from the decoder 71 is sent as it is to the memory 85 of the IC card recording system, and the remainder bit reduction circuit 84
, And is recorded on the IC card 2 via the IC card interface circuit 86. If, for example, the ATC data of the predetermined mode is recorded on the magneto-optical disk 1, the decoder 7
From 1 the quadrupled compressed data is read continuously.

Therefore, at the time of the above-mentioned high-speed dubbing, four times the real time from the magneto-optical disk 1 (in the above-mentioned predetermined mode).
Is obtained continuously, and this data is subjected to variable-length coding as it is and the IC card 2
, Four times faster dubbing can be realized.
Note that different compression modes have different dubbing speed magnifications. Also, dubbing may be performed at a high speed equal to or higher than the compression ratio. In this case, the magneto-optical disk 1 may be driven to rotate at a high speed several times higher than the steady speed.

Incidentally, the magneto-optical disk 1 has the structure shown in FIG.
As shown in FIG. 7, data compressed at a constant bit rate is recorded, and at the same time, the data amount obtained when the data is bit-compressed and encoded by the variable bit rate encoder 3 (that is, the data amount in the IC card 2). Information of the data recording capacity required for recording) is recorded. By doing so, for example, of the songs recorded on the magneto-optical disk 1, the number of songs or combination of songs that can be recorded on the IC card 2 can be immediately known by reading the data amount information. .

Conversely, in the IC card 2, not only the data compressed and coded at the variable bit rate but also
By recording the data amount information of the data that has been bit-compressed and encoded at a constant bit rate, it is possible to quickly know the data amount when data such as music is transmitted from the IC card 2 to the magneto-optical disk 1 and recorded. it can.

FIG. 3 shows a front external view of the compressed data recording / reproducing apparatus 5 having the configuration shown in FIG. 1, in which a magneto-optical disk insertion section 6 and an IC card insertion slot 7 are provided.

Next, with respect to the ATC encoder and decoder section of FIG. 1, an input digital signal such as an audio PCM signal is subjected to band division coding (SBC), adaptive conversion coding (ATC), and adaptive bit allocation (APC-AB). ) Will be described with reference to FIG. 4 and subsequent figures.

In the specific high efficiency coding apparatus shown in FIG. 4, the input digital signal is divided into a plurality of frequency bands by a filter or the like, and the higher the frequency band, the wider the bandwidth is selected. Conversion is performed, and the obtained spectrum data on the frequency axis is adaptively bit-allocated for each so-called critical bandwidth (critical band) in consideration of human auditory characteristics described later and encoded.
Of course, a band division width by a filter or the like may be an equal division width. Further, in the embodiment of the present invention, before the orthogonal transformation, the block size (block length) is adaptively changed according to the input signal, and the floating process is performed in units of the block.

That is, in FIG. 4, an audio PCM signal of, for example, 0 to 20 kHz is supplied to the input terminal 10. This input signal is divided into a band of 0 to 10 kHz and a band of 10 to 20 kHz by a band division filter 11 such as a so-called QMF filter, and a signal of the band 0 to 10 kHz is similarly divided by a band division filter 12 such as a so-called QMF filter. It is divided into a 5 kHz band and a 5 kHz to 10 kHz band. 10k from band division filter 11
The signal in the band of ~ 20 kHz is an MD which is an example of an orthogonal transformation circuit.
The signal is sent to a CT (Modified Discrete Cosine Transform) circuit 13 and is divided into a band division filter 1
5 to 10 kHz band signal from the MDCT circuit 14
, And the signals in the band of 0 to 5 kHz from the band division filter 12 are sent to the MDCT circuit 15 to be subjected to MDCT processing.

Regarding the above MDCT, for example, ICASSP,
1987, Subband / Transform CodingUsing Filter Bank De
signs Based on Time Domain Aliasing Cancellation,
JPPrincen, ABBradley, Modified DCT, Univ. Of S
urrey, Royal Melbourne Inst. of Tech.

Here, each of the MDCT circuits 13, 14, 15
FIG. 5 shows a specific example of a standard input signal for a block for each band to be supplied to. In the specific example of FIG. 5, the frequency band is widened and the time resolution is increased (the block length is shortened) toward the higher frequency side. That is,
1 block B for low-frequency 0-5 kHz band signal
Let L _L be 1024 samples, for example, and
For a signal in the 10 kHz band, the length T _{BL above}
Are divided into blocks BL _M1 and BL _M2 each having a half length T _BL / 2 of the block BL _L of the high frequency side 10k to
For a signal in the 20 kHz band, a block BL having a length T _BL / 4 of each of the above-mentioned low-side blocks BL _L is １ ／.
It is blocked by _H1 , BL _H2 , BL _H3 and BL _H4 .
When considering a band of 0 to 22 kHz as an input signal, the low band is 0 to 5.5 kHz and the middle band is 5.5 to 11 kHz.
kHz and the high frequency range is 11 to 22 kHz.

Referring again to FIG. 4, each MDCT circuit 13,
The spectrum data or MDCT coefficient data on the frequency axis obtained by the MDCT processing at 14 and 15 are collected for each so-called critical band (critical band) and sent to the adaptive bit allocation coding circuit 18. The critical band is a frequency band divided in consideration of human auditory characteristics, and a band of a pure tone when the pure tone is masked by a narrow band noise near the frequency of the pure tone. That is. The bandwidth of this critical band increases as the frequency increases, and the entire frequency band of 0 to 20 kHz is divided into, for example, 25 critical bands.

The allowable noise calculating circuit 20 calculates the allowable noise amount for each critical band in consideration of the so-called masking effect and the like based on the spectrum data divided for each critical band. The number of bits allocated to each critical band is determined based on the energy or peak value of the spectrum data, and the spectrum data (or MDCT coefficient) is calculated according to the number of bits allocated to each critical band by the adaptive bit allocation coding circuit 18. Data) is requantized. The data thus encoded is taken out via the output terminal 19.

FIG. 6 is a block circuit diagram showing a schematic configuration of a specific example of the allowable noise calculating circuit 20. In FIG. 6, spectrum data on the frequency axis is supplied to the input terminal 21 from each of the MDCT circuits 13, 14, and 15.

The input data on the frequency axis is sent to the energy calculating circuit 22 for each band, and the energy for each critical band (critical band) calculates, for example, the sum of the amplitude values in the band. It is required by things. Instead of the energy for each band, a peak value or an average value of the amplitude value may be used. As an output from the energy calculation circuit 22, for example, the spectrum of the sum value of each band is generally called a bark spectrum. FIG. 7 shows such a bark spectrum SB for each critical band. However, in FIG. 7, the number of the critical bands is represented by 12 bands (B _{1 to} B ₁₂ ) to simplify the illustration.

Here, in order to consider the influence of the bark spectrum SB on so-called masking, a convolution process is performed such that the bark spectrum SB is multiplied by a predetermined weighting function and added. Therefore, the output of the energy calculation circuit 22 for each band, that is, each value of the bark spectrum SB is sent to the convolution filter circuit 23. The convolution filter circuit 23 includes, for example, a plurality of delay elements for sequentially delaying input data,
It is composed of a plurality of multipliers (for example, 25 multipliers corresponding to each band) for multiplying the output from these delay elements by a filter coefficient (weighting function) and a sum adder for summing the outputs of the multipliers. Things. By this convolution processing, the sum of the parts shown by the dotted lines in FIG. 7 is obtained. In addition,
The masking refers to a phenomenon in which a certain signal masks another signal and makes it inaudible due to human auditory characteristics.The masking effect includes a time-axis masking effect by an audio signal on a time axis. At the same time by the signal on the frequency axis.
Due to these masking effects, even if there is noise in the masked portion, this noise will not be heard. For this reason, in an actual audio signal, noise within the masked range is regarded as acceptable noise.

Here, a specific example of the multiplication coefficient (filter coefficient) of each multiplier of the convolution filter circuit 23 will be described. When the coefficient of the multiplier M corresponding to an arbitrary band is set to 1, the multiplier M-1 is a coefficient of 0.15, multiplier M-2 is a coefficient of 0.0019, and multiplier M-3 is a coefficient of 0.00000.
086, a coefficient 0.4 by a multiplier M + 1, and a multiplier M + 2
By multiplying the output of each delay element by the coefficient 0.06 by the multiplier M + 3 and the coefficient 0.007 by the multiplier M + 3, the convolution process of the bark spectrum SB is performed. However, M is 1
It is an arbitrary integer of 25.

Next, the output of the convolution filter circuit 23 is sent to a subtractor 24. The subtracter 24 calculates a level α corresponding to an allowable noise level described later in the convolved area. The level α corresponding to the permissible noise level (permissible noise level)
Is a level which becomes an allowable noise level for each of the critical bands by performing the inverse convolution processing as described later. Here, an allowance function (a function expressing a masking level) for obtaining the level α is supplied to the subtractor 24. The level α is controlled by increasing or decreasing the allowable function. The permissible function is (n−
ai) It is supplied from the function generation circuit 25.

That is, the level α corresponding to the allowable noise level can be obtained by the following equation (1), where i is a number sequentially given from the lower band of the critical band. α = S− (n−ai) (1) In the equation (1), n and a are constants, a> 0, S is the intensity of the convolution-processed Bark spectrum, and (1)
In the equation, (n-ai) is the allowable function. In this embodiment, n = 38,
Since a = 1, there was no deterioration in sound quality at this time, and good encoding was performed.

In this way, the level α is obtained, and this data is transmitted to the divider 26. The divider 26 is for inversely convolving the level α in the convolved region. Therefore, by performing this inverse convolution processing,
The masking threshold can be obtained from the level α. That is, this masking spectrum becomes an allowable noise spectrum. Note that the above inverse convolution process requires a complicated operation, but in the present embodiment, the inverse convolution is performed using the simplified divider 26.

Next, the above-mentioned masking threshold is transmitted to the subtracter 28 via the synthesizing circuit 27. Here, the output from the energy detection circuit 22 for each band, that is, the above-described bark spectrum SB is supplied to the subtracter 28 via a delay circuit 29. Therefore, the subtraction operation of the masking threshold and the bark spectrum SB is performed by the subtracter 28, as shown in FIG.
Is masked below the level indicated by the level of the masking threshold MS.

The output from the subtracter 28 is taken out via an allowable noise correction circuit 30 and an output terminal 31.
For example, the assigned bit number information is sent to a ROM or the like (not shown) in which the information is stored in advance. The ROM or the like assigns each band in accordance with the output (the level of the difference between the energy of each band and the output of the noise level setting means) obtained from the subtraction circuit 28 via the allowable noise correction circuit 30. Output bit number information. By transmitting the allocated bit number information to the adaptive bit allocation coding circuit 18, the MDC
Each spectrum data on the frequency axis from the T circuits 13, 14, and 15 is quantized by the number of bits assigned to each band.

That is, in summary, the adaptive bit allocation coding circuit 18 calculates the number of bits assigned to each band in accordance with the level of the difference between the energy of each band of the critical band and the output of the noise level setting means. Each spectrum data is quantized. The delay circuit 29 is provided to delay the bark spectrum SB from the energy detection circuit 22 in consideration of the amount of delay in each circuit before the synthesis circuit 27.

By the way, at the time of synthesizing by the synthesizing circuit 27 described above, data indicating a so-called minimum audible curve RC, which is a human auditory characteristic as shown in FIG. The above-mentioned masking threshold MS can be synthesized. At this minimum audible curve, if the absolute noise level is below this minimum audible curve, the noise will not be heard. This minimum audible curve may differ, for example, due to differences in playback volume during playback, even if the coding is the same, but in a realistic digital system, the way in which music enters the 16-bit dynamic range, for example, varies significantly. If there is no quantization noise in the most audible frequency band around 4 kHz, for example, it is considered that quantization noise below the level of the minimum audible curve will not be heard in other frequency bands. Therefore, it is assumed that a method is used in which noise near the word length of the system, for example, around 4 kHz is not heard.
If the allowable noise level is obtained by combining C and the masking threshold MS together, the allowable noise level in this case can be up to the shaded portion in FIG. In this embodiment, the 4 kHz level of the minimum audible curve is adjusted to the lowest level corresponding to, for example, 20 bits. FIG.
Also shows the signal spectrum SS at the same time.

The allowable noise correction circuit 30 corrects the allowable noise level in the output from the subtracter 28 based on, for example, information on the equal loudness curve sent from the correction information output circuit 33. Here, the equal loudness curve is a characteristic curve relating to human auditory characteristics. For example, the loudness curve is obtained by calculating the sound pressure of sound at each frequency that sounds as loud as a pure tone of 1 kHz, and is connected by a curve. Also called a sensitivity curve. Further, this equal loudness curve draws substantially the same curve as the minimum audible curve RC shown in FIG. In this equal loudness curve, for example, the sound pressure near 8 kHz is 8
Even if it drops by 10 dB, it sounds the same as 1 kHz. Conversely, the sound pressure around 50 kHz is about 15 dB lower than the sound pressure at 1 kHz.
If it is not high, it will not sound the same size. For this reason, it can be seen that noise exceeding the level of the minimum audible curve (allowable noise level) preferably has a frequency characteristic given by a curve corresponding to the equal loudness curve.
From this, it can be seen that correcting the allowable noise level in consideration of the equal loudness curve is suitable for human auditory characteristics.

Here, as the correction information output circuit 33, the detection information of the output information amount (data amount) at the time of quantization in the encoding circuit 18 and the bit rate target value of the final encoded data are used. The allowable noise level may be corrected based on the error information. This is because the total number of bits obtained by previously performing temporary adaptive bit allocation for all bit allocation unit blocks is a fixed number of bits (target value) determined by the bit rate of the final encoded output data. May have an error, and the bits are allocated again so that the error becomes zero. That is, when the total number of allocated bits is smaller than the target value, the difference bit number is allocated to each unit block and added. When the total allocated bit number is larger than the target value, the difference bit number is set to each unit block. It is to be allocated and cut.

To do this, an error of the total allocated bit number from the target value is detected, and the correction information output circuit 33 corrects each of the allocated bit numbers according to the error data. Is output. Here, when the error data indicates that the number of bits is insufficient, it is possible to consider a case where the data amount is larger than the target value by using a large number of bits per unit block. Further, when the error data is data indicating the remainder of the number of bits, a case where the number of bits per unit block is small and the data amount is smaller than the target value can be considered. Therefore, from the correction information output circuit 33, the allowable noise level in the output from the subtractor 28 is corrected based on the information data of the equal loudness curve, for example, according to the error data. Data will be output. By transmitting the correction value as described above to the allowable noise correction circuit 30, the allowable noise level from the subtractor 28 is corrected. In another embodiment, the bits of the target value may be fixedly assigned to each block from the beginning. At this time, a large reduction in the amount of calculation can be obtained. In still another embodiment, bits can be assigned depending on the signal size of each block. In this case, the noise energy can be minimized.

FIG. 10 is a block diagram of the surplus bit reducing circuit 8.
4 shows a specific example of the removable bit reduction circuit 101 corresponding to No. 4. In FIG. 10, A shown in FIG.
The output from the TC encoder 63 is an MDCT coefficient a,
It consists of bit length information b and floating information c. The bit length information “b” indicates what bit length the MDCT coefficient “a” is quantized, and the floating information “c” indicates what normalization processing is performed on the MDCT coefficient “a”. ATC encoder 6
The removal of the audibly redundant portion or the removal of the degree of redundancy contained in the output from 3 is performed as follows.

First, by using the floating information c and the MDCT coefficient a to obtain the coefficient size of each block, the masking threshold calculation circuit 102 performs masking using the method described with reference to FIG. Calculate the threshold. Next, the bit length calculation circuit 103 calculates the bit length in the same manner as described with reference to FIG.
The removable bit calculation circuit 104 extracts a removable bit portion by comparing with the bit length information b of the ATC encoder output. The final bit length determination circuit 106
The bit length information b of the ATC encoder output is compared with the output from the removable bit calculation circuit 104 to determine the final bit length, and the removable bit removal circuit 105 is controlled.
The MDCT coefficient a ′ from which the removable bits have been removed by the removable bits removing circuit 105, the floating information c, and the final bit length information b ′ output from the final bit length determining circuit 106 are, for example, as shown in FIG. To the IC card interface circuit 86 or the like.

The present invention is not limited to only the above embodiment. For example, the reproducing system for the one recording medium and the recording system for the other recording medium need not be integrated. It is also possible to connect between them with a data transfer cable. Further, the present invention is applicable not only to audio PCM signals but also to signal processing devices for digital voice (speech) signals and digital video signals. Further, the configuration may be such that the above-described minimum audible curve synthesis processing is not performed. In this case, the minimum audible curve generating circuit 32 and the synthesizing circuit 27 become unnecessary, and the output from the subtractor 24 is
After being deconvolved by the divider 26, it is immediately transmitted to the subtracter 28. Further, by driving the magneto-optical disk 1 at a rotation speed higher than the steady speed, dubbing at a higher speed than the bit compression ratio may be performed. In this case, high-speed dubbing can be performed within a range allowed by the data transfer speed. Further, as the other recording medium, other than the IC memory card,
Various types of I such as IC memory cartridges and IC memory packs
C memory can be used.

[0071]

As is apparent from the above description, according to the signal processing method of the present invention, a bit that gives an inaudible quantization noise level from a signal that has been bit-compressed at a constant bit rate. Has been removed in the form of bit-compressed samples in small blocks subdivided in time and frequency,
It is possible to increase the compression efficiency and reduce the data amount while suppressing the deterioration of the sound quality.

Further, according to the compressed data recording / reproducing apparatus of the present invention, the bit-compressed digital data is reproduced from one recording medium (such as a magneto-optical disk), and the bit-compressed digital data is directly subjected to the bit decompression processing. Rather than performing a bit compression process at a variable bit rate, other recording media (for example, IC
Since the data is directly recorded on the card, so-called high-speed dubbing according to the compression ratio can be performed, and dubbing can be performed efficiently in a short time.

The variable bit rate bit compression is performed by a high-efficiency code for quantizing a sample in a small block subdivided with respect to time and frequency, and is applied to a bit which gives a noise level below a masking threshold. , In the form of bit-compressed samples in small blocks subdivided in time and frequency, it is possible to greatly reduce the data amount while suppressing sound quality deterioration, and to reduce the It is economical even when recording on an expensive recording medium with a high bit unit price.

In addition, on one recording medium such as a magneto-optical disk, at the same time as data compressed and encoded at a constant bit rate, data amount information at the time of compression encoding at the data variable bit rate is recorded. Or I
By recording the variable bit rate compression-encoded data and the data amount information at the time of compression-encoding at a constant bit rate on another recording medium such as a C card, the number of songs and the optimum combination when transferring songs Can be instantly known.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a configuration example of a compressed data recording / reproducing apparatus as one embodiment of the present invention.

FIG. 2 is a diagram showing recorded contents of a magneto-optical disk 1 and an IC card 2.

FIG. 3 is a schematic front view showing an example of an external appearance of the embodiment device.

FIG. 4 is a block circuit diagram showing a specific example of a high-efficiency compression encoding device that can be used for constant bit rate compression encoding in the above embodiment.

FIG. 5 is a diagram showing a specific example of divided bands and blocking in the time axis direction in each band in the apparatus of FIG. 4;

6 is a block circuit diagram showing a specific example of an allowable noise calculation circuit 18 of the device shown in FIG.

FIG. 7 is a diagram showing a bark spectrum.

FIG. 8 is a diagram showing a masking spectrum.

FIG. 9 is a diagram in which a minimum audible curve and a masking spectrum are combined.

FIG. 10 is a block circuit diagram showing a specific example of a remainder bit reducing circuit.

[Explanation of symbols]

1 ... Magneto-optical disk 2 ... IC card 11, 12 ... Band splitting filter 13, 14, 15 ... Orthogonal transform circuit (MDCT circuit) 18 ... · Adaptive bit allocation coding circuit 20 · · · · permissible noise calculation circuit 22 · · · Energy detection circuit for each band 23 · · · · convolution filter circuit 27 · · · · synthesis circuit 28 · · · ... Subtractor 30 ... Permissible noise correction circuit 32 ... Minimum audible curve generation circuit 33 ... Correction information output circuit 53 ... Optical head 54 ... Magnetic head 56 Servo control circuit 57 System controller 62, 83 A / D converter 63 ATC encoder 64, 72, 85 ... Memory 65 ... Encoder 66 ... · Magnetic head drive circuit 71 · · · · Decoder 73 · · · · ATC decoder 74 · · · D / A converter 84 · · · surplus bit reduction circuit 86 · · · · · · IC card interface Circuit 101: Removable bit reduction circuit 102: Masking threshold calculation circuit 103: Removable bit calculation circuit 104: Removable bit removal circuit 105: ..Last bit length determination circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-201526 (JP, A) JP-A-63-201700 (JP, A) JP-A-3-117919 (JP, A) JP-A-3-301 117921 (JP, A) JP-A-3-132217 (JP, A) JP-A-3-132219 (JP, A) JP-A-2-501507 (JP, A) International publication 90/9022 (WO, A1) International Published 90/9064 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03M 7/30

Claims (12)

(57) [Claims] 1. A signal processing method for further compressing a signal that has been bit-compressed at a constant bit rate, the signal comprising: a high-efficiency code for quantizing samples in a small block subdivided in time and frequency; From the bit-compressed signal at the bit rate, at least some of the bits giving the inaudible quantization noise level are converted in the form of bit-compressed samples in small blocks subdivided in time and frequency. Signal processing method to remove. 2. A signal processing method for further compressing a signal which has been bit-compressed at a constant bit rate, wherein the constant-rate coding is performed by a high-efficiency code for quantizing samples in a small block subdivided in time and frequency. At least a part of the bits that give a quantization noise level below the allowable noise level determined by the masking threshold and minimum audibility from the signal that has been bit-compressed at the bit rate, in a small block subdivided in time and frequency. Signal processing method in the form of bit-compressed samples. 3. The signal processing method according to claim 1, wherein the bit rate of the data bit-compressed by the bit removal is a variable bit rate. 4. A compressed data recording / reproducing apparatus having a compressed data recording system for further compressing a signal which has been bit-compressed at a constant bit rate and recording the signal on a recording medium, wherein the signal which has been bit-compressed at the constant bit rate 3. A compressed data recording / reproducing apparatus which performs bit compression processing at a variable bit rate by the signal processing method according to claim 1 or 2 and records the compressed data on the recording medium. 5. A reproduction system for reproducing a bit-compressed signal at a constant bit rate on one recording medium, and a recording system for further compressing the reproduced compressed data and recording it on another recording medium. 3. A compressed data recording / reproducing apparatus comprising: a compressed data reproduced from the one recording medium being subjected to bit compression processing at a variable bit rate by the signal processing method according to claim 1 or 2; A compressed data recording / reproducing apparatus characterized by recording on a medium. 6. The compressed data recording / reproducing apparatus according to claim 4, wherein said recording medium is an IC memory or an IC memory card. 7. The compressed data recording / reproducing apparatus according to claim 5, wherein said one recording medium is a disk, and the other recording medium is an IC memory or an IC memory card. 8. The bit compression processing for recording on the recording medium or the other recording medium is performed by using a total number of bits that gives an allowable noise determined by a masking threshold and a minimum audibility and a total number of bits that can be used. 6. The compressed data recording / reproducing apparatus according to claim 4, wherein a high-efficiency coding method for giving a noise characteristic in which an allowable noise spectrum is changed by a difference is provided. 9. The data recording method according to claim 4, wherein, when performing bit compression recording at a variable bit rate on the recording medium, data amount information of a bit rate before variable bit rate processing is recorded. Compressed data recording / reproducing device. 10. The compressed data recording according to claim 6, wherein the one recording medium records data amount information for performing bit compression recording at a variable bit rate on the other recording medium. Playback device. 11. The recording medium according to claim 7, wherein the other recording medium has recorded therein data amount information of digital data bit-compressed and recorded at a constant bit rate on the one recording medium. Compressed data recording / reproducing device. 12. The compressed data recording / reproducing apparatus according to claim 1, wherein a high-efficiency code having floating information and bit length information as sub-information is used.