JP2007181208A - Apparatus for data compression and expansion of audio signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an audio signal compression apparatus by a simpler structure and at lower cost. <P>SOLUTION: A data compression apparatus for data compressing an audio signal includes an input terminal 1 for receiving the audio signal, an A-D converter 4 for converting the audio signal so as to obtain a bit-stream signal, a lossless coder 10 for executing lossless data compression processing on the bit-stream signal to obtain a data compressed bit-stream signal, and an output terminal 14 for outputting the data compressed bit-stream signal. Further, a recording apparatus and a transmitter apparatus including the data compression apparatus are disclosed. In addition, a data expansion apparatus for data expanding the data compressed bit-stream signal supplied by the data compression apparatus is disclosed, and a reproducing apparatus and a receiver apparatus including the data expansion apparatus are disclosed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a data compression apparatus for compressing data of an audio signal, a data compression method, a transmitter having a data compression apparatus, a recording apparatus having a data compression apparatus, and a recording in which a compressed audio signal is recorded on a track of the medium The present invention relates to a medium, a data decompression device for decompressing data-compressed audio signals, a data decompression method, a receiver having a data decompression device, and a playback device having a data decompression device.

  Conventionally, data compression techniques for audio signals are well known. Reference is made to EP-A 402,973 of document D1 in the list of related documents. Such a document describes a sub-band coder, in which the audio signal is A / D converted at a specific sampling frequency such as 44.1 kHz, for example sample data obtained in the form of a 24-bit wide word audio signal. Is supplied to the subband splitting filter. The subband division filter divides the wideband digital audio signal into a plurality of relatively narrow band subband signals. Using a psychological acoustic model, a masked threshold is obtained, and then a sub-band signal sample block is quantized with a specified number of bits per sample for each block of the sub-band signal according to the masked threshold Is done. This achieves effective data compression of the audio signal to be transmitted. The data compression performed here is a lossy compression method because it is performed by “discarding” inaudible signal components in the audio signal. The data compression described in the document D1 is a highly efficient data compression method, and when this compression is realized by hardware or software, a considerable number of gates or instructions are required, respectively. It will be something. Furthermore, decompressors that handle subsequent processing also require a significant number of gates or instructions, respectively, when implemented in hardware or software.

  It is an object of the present invention to provide a data compression apparatus that compresses an audio signal with a simple configuration and that the corresponding expansion apparatus is simple and inexpensive.

  A data compression apparatus according to the present invention includes:

  Input means for receiving the audio signal;

  Conversion means having sigma / delta modulation means for converting the audio signal so as to obtain a 1-bit bit stream signal;

  Lossless encoding means for applying a substantially lossless data compression process to the bitstream signal to obtain a data compressed bitstream signal;

  Output means for outputting the data compressed bit stream signal. More specifically, when the audio signal is an analog audio signal, the conversion unit is an A / D conversion unit that performs 1-bit A / D conversion on the analog audio signal so as to obtain the bit stream signal. Is taken.

  The present invention is based on the following recognition. The audio signal can be supplied in analog or digital form. According to the present invention, when an analog audio signal is converted by a 1-bit A / D converter (also referred to as a bit stream converter or a sigma / delta modulator), the audio signal to be A / D converted is , Typically sampled at a frequency that is a multiple of 44.1 kHz or 48 kHz. The output signal of the 1-bit A / D converter is a binary signal called a bit stream signal. If the audio signal is, for example, 44.1 kHz samples and each sample value is supplied in a digital format, for example represented by 16 bits per sample, this digital signal will also have this 44.1 kHz (or 48 kHz) sampling frequency. Oversampled at multiples of. Thereby, a 1-bit bit stream signal is obtained.

  There are several advantages to converting an audio signal into a 1-bit bitstream signal. Bitstream conversion is a high-quality encoding method that allows high-quality decoding or low-quality decoding that can simplify the decoding circuit. As a reference material, the publication “A digital decimation filter for analog-to-digital conversion of hi” was published by JJ van der Kam in document D2 in the list of related documents. -fi audio signals) and publication D3 in the list of related documents by Kirk CH Chao et al., “A higher order topology for interstitial modulators in oversampling A / D converters” interpolative modulators for oversampling A / D converters).

  The 1-bit D / A converter is used in a CD player and, for example, reversely converts the bit stream audio signal into an analog audio signal. However, the audio signal recorded on the CD disc is not a data-compressed 1-bit bit stream signal.

  It is well known in the art that the output bitstream signal of a 1-bit A / D converter is generally said to be a random signal having a “noise-like” frequency spectrum. This type of signal is difficult to compress data.

  However, surprisingly, a lossless coder such as a variable length coder that takes the form of a Huffman coder or an arithmetic coder is used even though the bit stream signal from the 1-bit A / D converter is noisy. It was proved that effective data reduction was possible.

  These and other aspects of the invention will be apparent from and will be elucidated with reference to the embodiments described in the description of the following drawings.

  FIG. 1 shows an embodiment of a data compression device, which has an input terminal 1 for receiving an audio signal. In this example, the audio signal is an analog audio signal. The input terminal 1 is connected to an input terminal 2 of a 1-bit A / D converter 4 (also called a sigma / delta modulator). The output terminal 6 of the 1-bit A / D converter 4 is connected to the input terminal 8 of the data compression unit 10. The output terminal 12 of the data compression unit 10 is connected to the output terminal 14.

The 1-bit A / D converter 4 is configured to perform 1-bit A / D conversion on the audio signal so that a bit stream signal can be obtained. Therefore, the A / D converter 4 receives a sampling frequency equal to N · f _S via the input terminal 16. Here, f _S is a frequency equal to, for example, 32 kHz, 44.1 kHz, or 48 kHz, and N is a large number such as 64. The audio signal is sampled by the A / D converter 4 at a sampling frequency of, for example, 2.8224 MHz (64 × 44.1 kHz). Therefore, the bit stream signal appearing at the output terminal 6 of the A / D converter has a bit rate of 2.8224 MHz.

  The data compression unit 10 is in the form of a lossless coder. The lossless coder has the advantage that the audio signal can be compressed so that the original audio signal can be restored in a substantially lossless manner after the data is decompressed by the lossless decoder. There is something. This means that there is no substantial loss of information after compression-decompression. The lossless coder can take the form of a variable length coder. Variable length coders are well known in the art. Examples of such variable length coders include Huffman coders, arithmetic coders, and Lempel-Ziv coders. In this regard, “A method for the construction of minimum-redundancy codes” by DA Huffman of document D4 in the list of related documents, document D5 in the list of related documents. "General introduction algorithm for compression of sequential data" by "An introduction to arithmetic coding" by GG Langdon and J. Ziv of document D6 in the list of related documents (A universal algorithm for sequential data compression) is helpful.

  The data compression unit 10 performs a substantially lossless data compression process on the bit stream signal to obtain a data compressed bit stream signal at its output 12. This data compressed bit stream signal is supplied to the output terminal 14.

  FIG. 2A shows a frequency spectrum of the bit stream signal appearing at the output terminal 6 of the A / D converter 4 when sampling is performed at a sampling frequency of 2.8224 MHz with respect to a 5 kHz sinusoidal input signal. Therefore, this spectrum shows frequencies from 0 Hz to 1.4 MHz. FIG. 2B shows a part of the spectrum shown in FIG. 2A, that is, the part from 0 kHz to 100 kHz. This is to more clearly show the 5 kHz sine wave included in the bit stream signal. Obviously, the noise characteristics of the bit stream signal can be seen especially in the high frequency range. This seems to mean that data compression of this signal does not result in significant data reduction.

  In contrast, research has shown that effective data reduction can be achieved.

ここで、δは、コーダの入力信号のビットレートの、コーダの出力信号のビットレートに対する比として定義される圧縮比である。 The table below shows the data compression results performed by three lossless coders for three different songs.

Here, δ is a compression ratio defined as the ratio of the bit rate of the coder input signal to the bit rate of the coder output signal.

  FIG. 3 shows an embodiment of a recording apparatus having the data compression apparatus shown in FIG. The recording apparatus further includes a writing unit 30 that writes a data compressed bit stream signal to a track of the recording medium 32. In the example presented here, since the recording medium 32 is a magnetic recording medium, the writing unit 30 has at least one magnetic head 34 for writing a data compressed bit stream signal to the recording medium 32. However, the recording medium may be an optical recording medium such as a CD disk or a DVD disk.

  FIG. 4 shows an embodiment of a transmitter for transmitting an audio signal via a transmission medium TRM, which has a data compression device as shown in FIG. The transmitter further comprises a transmission unit 40 for sending the data compressed bit stream signal to the transmission medium TRM. The transmission unit 40 can have an antenna 42.

  In general, transmission via a transmission medium such as a radio frequency link or a recording medium requires error correction coding processing and channel coding processing performed on a data compressed bit stream signal to be transmitted. FIG. 8 shows such signal processing performed on the data compressed bit stream signal in the recording apparatus of FIG. That is, the recording apparatus of FIG. 8 has an error correction encoder 80 well known in the art, and also has a well known channel encoder 82.

  FIG. 5 shows an embodiment of the data decompression apparatus. This device comprises an input terminal 50 for receiving a data compressed audio signal in the form of a data compressed bitstream signal as supplied by the data compression device of FIG. The input terminal 50 is connected to the input terminal 52 of the data decompression unit 54, and the unit 54 includes an output terminal 56 connected to the input terminal 58 of the 1-bit D / A converter 60. The output terminal 62 of the converter 60 is connected to the output terminal 64.

  The data decompression unit 54 is a lossless decoder such as a variable length decoder taking the form of a Huffman decoder or an arithmetic decoder, for example. In order to realize a substantially lossless encoding / decoding process, it is apparent that the decoder in the data decompression apparatus of FIG. 5 is the reverse of the encoder used in the data compression apparatus of FIG. is there. The data decompression unit 54 decompresses the data compression bit stream signal to reproduce the original bit stream signal, and supplies it to the input terminal 58 of the D / A converter 60. The converter 60 converts the bit stream signal into an analog audio signal and supplies it to the terminal 64.

  FIG. 6 shows the data decompression apparatus of FIG. 5 incorporated in the playback apparatus. The reproducing apparatus further includes a reading unit 70 for reading the data compressed bit stream signal from the track of the recording medium 32. In this example, since the recording medium 32 is a magnetic recording medium, the reading unit 70 has at least one magnetic head 72 for reading a data compressed bit stream signal from the recording medium 32. However, the recording medium may be an optical recording medium such as a CD disk or a DVD disk.

  FIG. 7 shows an embodiment of a receiver having a data decompression apparatus as shown in FIG. 5 and receiving an audio signal via a transmission medium TRM. The receiver further comprises a receiving unit 75 for receiving the data compressed bitstream signal from the transmission medium TRM. The receiving unit 75 may have an antenna 77.

  As described above, transmission over a transmission medium such as a radio frequency link or recording medium generally requires error correction coding and channel coding performed on the data compressed bitstream signal to be transmitted. In reception, channel decoding and error correction corresponding to them can be performed. FIG. 9 shows signal processing steps of channel coding and error correction performed on the received signal received by the reading means 70 in the reproducing apparatus of FIG. That is, the reproducing apparatus of FIG. 9 has a channel decoder 90 known in this technical field and an error correction unit 92 which is also well known, thereby obtaining a reproduction signal of the data compressed bit stream signal.

  Another data compression apparatus is shown in FIG. In this data compression apparatus of FIG. 10, the bit stream signal is supplied to the input terminal 8 of the lossless coder. Such a coder takes the form of an entropy coder such as arithmetic coder 154. Further, this bit stream signal is input to the prediction filter unit 152. The output terminal of the prediction filter unit 152 is connected to the input terminal of the probability determination unit 156. The arithmetic coder 154 encodes the bit stream signal into a data compressed bit stream signal according to the probability value P supplied to the input terminal 192. The probability determination unit 156 determines a probability value indicating a probability that a bit of the bit stream signal supplied by the converter 4 exhibits a predetermined logical value such as “1”. The probability value P shown in FIG. 10 is supplied to the arithmetic coder 154, which enables data compression of the bit stream signal in the arithmetic coder 154. The determination unit 156 determines a probability value from the output signal of the prediction filter 152. The arithmetic coder 154 can compress the bit stream signal for each frame.

  The operation of the apparatus of FIG. 10 is as follows. The prediction filter 152 performs prediction filtering on the bit stream signal so as to obtain a multi-bit output signal. This multi-bit output signal has a plurality of levels within a range of, for example, +3 to -3. Further, for each of a plurality of partial intervals in the value range of the multi-bit output signal, the probability that the corresponding bit in the bit stream signal is, for example, “1” is determined. This can be achieved by counting the number of “1” s and “0” s that occur in the bitstream signal at a predetermined time interval when the multi-bit output signal falls into one of such ranges. The probabilities thus obtained for the various values in the multi-bit output signal are then supplied as a probability signal P to the arithmetic coder 154. The data compressed bit stream signal is supplied to the output line 158 by the arithmetic coder 154 so as to be transmitted via the transmission medium TRM or the recording medium.

  FIG. 11 shows a corresponding data decompression device for decoding a data compressed bitstream signal received via the transmission medium TRM. The data processing apparatus in FIG. 11 has an entropy decoder 172. The entropy decoder receives the data compressed bit stream signal via the input 174. In this example of presentation, the entropy decoder 172 generates a data compression bitstream signal based on the action of the probability signal P supplied to the input 176 so that a reproduction signal of the original bitstream signal is generated at the output 178. An arithmetic decoder that performs arithmetic decoding processing is employed. This reproduction signal is supplied to the input terminal 58 of the inverse conversion unit 60.

  Further, the probability supplying unit 180 is for supplying a probability signal P to the arithmetic decoder 172. The probability signal P can be obtained by various methods depending on how the probability signal is acquired by the encoder. One method is to obtain a probability signal P from the output signal of the prediction filter 181 by adaptive processing. In this embodiment, the prediction filter 181 is equivalent to the prediction filter 152 in the encoder, and the probability supply unit 180 is equivalent to the probability determination unit 156 in the encoder of FIG. Another way of generating the probability signal P is by using sub-information received via the transmission medium TRM, as will be explained below.

  Sub-information can be generated by the device of FIG. 10 for the purpose of transmission to the device of FIG. Such sub-information can include the filter coefficients of the filter 152 determined for each frame, and such coefficients are sent to the corresponding prediction filter included in the unit 180.

  Furthermore, the apparatus of FIG. 10 can generate a parameter describing the conversion of the multi-bit output signal of the prediction filter 152 into the probability signal P. Such parameters are also included in the sub information and sent to the supply unit 180 and the filter 181. This allows the probability signal P to be regenerated in the apparatus of FIG. 11 based on the multi-bit output signal provided by the prediction filter 181.

  The entropy encoder used in the embodiment of FIG. 10 is configured to encode the bitstream signal using a probability signal to obtain a data compressed bitstream signal. One such entropy encoder is an arithmetic coder as described above. One other type of such entropy encoder is, for example, the well-known finite state coder. The entropy decoder used in the embodiment of FIG. 11 is configured to decode the data compressed bitstream signal using the probability signal to obtain a reproduction signal of the bitstream signal. One such entropy decoder is the arithmetic decoder described above. One other type of entropy decoder is, for example, the well-known finite state decoder.

  So far, while the invention has been described in terms of various preferred embodiments, it is to be understood that these are not limiting examples. That is, it will be apparent to those skilled in the art that various modifications can be made without departing from the scope of the invention as defined in the claims. If the audio signal is sampled at 44.1 kHz and the sample value is supplied in digital form, for example represented by 16 bits, the converting means may be, for example, 64 × 44. The digital audio signal is configured to be oversampled at a frequency of 1 kHz.

  In addition, the present invention is an implementation in which a signal processing step is performed on the bit stream signal as supplied by the converter 4 to obtain a processed 1-bit bit stream signal supplied to the lossless coder 10. The example also fits. This added signal processing step includes a merge process for integrating the left and right signal components of the 1-bit bit stream format stereo audio signal into the processed 1-bit bit stream signal.

In addition, the invention resides in each new feature or combination of features.
[List of related documents]
(D1) EP-A 402,973 (PHN 13.241)
(D2) 'A digital decimating filter for analog-to-digital conversion of hi-fi audio signals', by JJ van der Kam in Philips Techn. Rev. 42, no. 6/7, April 1986, pp. 230-8
(D3) 'A higher order topology for interpolative modulators for oversampling A / D converters', by Kirk CH Chao et al in IEEE Trans. On Circuits and Systems, Vol 37, no. 3, March 1990, pp. 309-18
(D4) 'A method for the construction of minimum-redundancy codes', by DA Huffman in Proc. Of the IRE, Vol. 40 (10), September 1952.
(D5) 'An introduction to arithmetic coding' by GG Langdon, IBM J. Res. Develop., Vol. 28 (2), March 1984.
(D6) 'A universal algorithm for sequential data compression' by J. Ziv et al, IEEE TRans. On Inform. Theory, Vol. IT-23, 1977.

1 shows an embodiment of a data compression apparatus. The figure which shows the frequency spectrum of the output signal of a 1 bit A / D converter. The figure which shows the frequency spectrum in the small frequency range of the same output signal. The figure which shows the data compression apparatus incorporated in the recording device which records the bit stream signal by which data compression was carried out on the recording medium. The figure which shows the data compression apparatus incorporated in the transmitter which transmits the bit stream signal by which data compression was carried out via the transmission medium. The figure which shows the Example of a data expansion | extension apparatus. The figure which shows the data expansion | extension apparatus integrated in the reproducing | regenerating apparatus which reproduces | regenerates the bit stream signal by which data compression was performed from the recording medium. The figure which shows the data expansion | extension apparatus incorporated in the receiver which receives the bit stream signal by which data compression was carried out from the transmission medium. The figure which shows the recording device of the other Example in which the error correction encoder and the channel encoder were further provided. The figure which shows the reproducing | regenerating apparatus of the other Example further provided with the channel decoder and the error correction unit. The figure which shows the Example of the data compression apparatus provided with the lossless coder which takes the form of arithmetic coder. The figure which shows the Example of the data expansion | deployment apparatus provided with the lossless decoder which takes the form of an arithmetic decoder.

Claims (30)

In a data compression device for compressing data of an audio signal,
Input means for receiving the audio signal;
Conversion means having sigma / delta modulation means for converting the audio signal so as to obtain a 1-bit bit stream signal;
Lossless encoding means for applying a substantially lossless data compression process to the bitstream signal to obtain a data compressed bitstream signal;
Output means for outputting the data compressed bit stream signal;
A data compression apparatus comprising: The data compression apparatus according to claim 1, wherein
The audio signal is an analog audio signal, and the conversion means is configured as an A / D conversion means for performing 1-bit A / D conversion on the analog audio signal so as to obtain the bit stream signal. A data compression apparatus characterized by the above. The data compression device according to claim 1 or 2,
The lossless encoding means includes a variable length coder. The data compression apparatus according to claim 3, wherein
The data compression apparatus, wherein the variable length coder is a Huffman coder. The data compression apparatus according to claim 3, wherein
The data compression apparatus, wherein the variable length coder is an arithmetic coder. In a data compression method for compressing an audio signal,
Receiving the audio signal;
A conversion step having a sigma / delta modulation step and converting the audio signal to obtain a 1-bit bitstream signal;
Subjecting the bitstream signal to a substantially lossless data compression process to obtain a data compressed bitstream signal;
Outputting the data compressed bitstream signal;
A data compression method comprising: A transmitter having the data compression device according to any one of claims 1 to 5 and transmitting an audio signal via a transmission medium,
The transmitter further comprising a transmission means for outputting the data compressed bit stream signal to the transmission medium. A recording apparatus for recording an audio signal on a recording medium, comprising the data compression apparatus according to claim 1.
The recording apparatus further comprising writing means for writing the data compressed bit stream signal to a track of the recording medium. The recording apparatus according to claim 8, wherein
The recording apparatus is an optical or magnetic recording medium.   A recording medium, wherein a data compressed bit stream signal is recorded on a track of the recording medium. In a data decompression device that decompresses a data-compressed audio signal so as to obtain a reproduction signal of the original audio signal,
Input means for receiving a data compressed audio signal in the form of a data compressed bitstream signal;
Lossless decoding means for performing a substantially lossless data decompression process on the data compressed bitstream signal to obtain a bitstream signal;
D / A conversion means for performing D / A conversion on the bit stream signal so as to obtain the reproduction signal of the original audio signal;
Output means for outputting the reproduction signal of the original audio signal;
A data decompression device comprising: The data decompression device according to claim 11, wherein
The D / A conversion means has a sigma / delta demodulator, characterized in that the data expansion apparatus. The data decompression device according to claim 11 or 12,
The lossless decoding means includes a variable length decoder. The data decompression device according to claim 13,
The data decompression apparatus, wherein the variable length decoder is a Huffman decoder. The data decompression device according to claim 13,
The data decompression device, wherein the variable length decoder is an arithmetic decoder. In a data decompression method for decompressing a data compressed audio signal so as to obtain a reproduction signal of an original audio signal,
Receiving a data compressed audio signal in the form of a data compressed bitstream signal;
Subjecting the data compressed bitstream signal to a substantially lossless data decompression process to obtain a bitstream signal;
Performing D / A conversion on the bit stream signal so as to obtain the reproduction signal of the original audio signal;
Outputting a reproduction signal of the original audio signal;
A data decompression method comprising: A receiver having the data expansion device according to any one of claims 11 to 15 and receiving an audio signal via a transmission medium,
The receiver further comprising receiving means for obtaining the data compressed bit stream signal from the transmission medium. A playback device that includes the data expansion device according to claim 11 and plays back an audio signal from a recording medium.
A reproducing apparatus, further comprising reading means for reading the data compressed bit stream signal from a track of the recording medium. The transmitter of claim 7, wherein
Error correction coding means and / or channel coding means for error correction coding and / or channel coding of the data compression bitstream signal before outputting the data compression bitstream signal to the transmission medium. Features transmitter. The recording apparatus according to claim 8, wherein
It further comprises error correction coding means and / or channel coding means for performing error correction coding and / or channel coding of the data compressed bit stream signal before writing the data compressed bit stream signal to the recording medium. A recording device. The receiver according to claim 17, wherein
A receiver further comprising channel decoding means and / or error correction means for obtaining a data compressed bitstream signal by channel decoding and / or error correction of a signal acquired from the transmission medium. The playback device according to claim 18, wherein
A reproduction apparatus further comprising channel decoding means and / or error correction means for obtaining a data compressed bit stream signal by channel decoding and / or error correction of a signal read from the recording medium. In a data compression device for compressing data of an audio signal,
Input means for receiving the audio signal;
Conversion means having sigma / delta modulation means for converting the audio signal so as to obtain a 1-bit bit stream signal;
Lossless encoding means for applying a substantially lossless data compression process to the bitstream signal to obtain a data compressed bitstream signal;
Output means for outputting the data compressed bitstream signal,
The lossless encoding means includes
An entropy encoder that entropy encodes the bitstream signal in response to a probability signal to obtain the data compressed bitstream signal;
Prediction means for performing prediction processing on the bit stream signal;
Probability signal determination means for determining the probability signal based on the prediction means,
A data compression apparatus. The data compression device according to claim 23,
The prediction means includes prediction filter means for performing a prediction filter process on the bitstream signal so as to obtain a multi-value output signal;
The data compression apparatus characterized in that the probability determination means is configured to obtain the probability signal from the multilevel output signal. In a data compression method for compressing an audio signal,
Receiving the audio signal;
Having a sigma / delta modulation step and converting the audio signal to obtain a 1-bit bitstream signal;
Subjecting the bitstream signal to a substantially lossless data compression process to obtain a data compressed bitstream signal;
Outputting the data compressed bit stream signal,
The lossless compression step includes:
An entropy encoding step of entropy encoding the bitstream signal according to a probability signal to obtain the data compressed bitstream signal;
A prediction step of performing a prediction process on the bitstream signal;
A probability determining step of determining the probability signal based on the predicting step,
A data compression method. The data compression method according to claim 25,
The prediction step includes a sub-step of performing a prediction filter process on the bit stream signal so as to obtain a multilevel output signal,
The data compression method according to claim 1, wherein the probability determination step includes a sub-step of obtaining the probability signal from the multilevel output signal. In a data decompression device that decompresses a data-compressed audio signal so as to obtain a reproduction signal of the original audio signal,
Input means for receiving the data compressed audio signal in the form of a data compressed bitstream signal;
Lossless decoding means for performing a substantially lossless data decompression process on the data compressed bitstream signal to obtain a bitstream signal;
D / A conversion means for performing D / A conversion on the bit stream signal so as to obtain the reproduction signal of the original audio signal;
Output means for outputting the reproduction signal of the original audio signal,
The lossless decoding means includes
An entropy decoder for entropy decoding the data compressed bitstream signal in response to a probability signal to obtain the bitstream signal;
Probability signal generating means for outputting the probability signal;
A data decompression device characterized by that.   28. The data expansion device according to claim 27, wherein the entropy decoder is an arithmetic decoder. In a data decompression method for decompressing a data compressed audio signal so as to obtain a reproduction signal of an original audio signal,
Receiving the data compressed audio signal in the form of a data compressed bitstream signal;
Subjecting the data compressed bitstream signal to a substantially lossless data decompression process to obtain a bitstream signal;
Performing D / A conversion on the bit stream signal so as to obtain the reproduction signal of the original audio signal;
Outputting the reproduction signal of the original audio signal,
The lossless decoding step comprises:
Sub-entropy decoding the data compressed bitstream signal in response to a probability signal to obtain the bitstream signal;
Outputting the probability signal.
A data decompression method.   30. The data decompression method according to claim 29, wherein the entropy decoding step is an arithmetic decoding step.

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