Method for data compression and expansion, device for data compression and expansion, transmitter and receiver, recording and reproducing device as well as sound signal carrier

Description of the invention

The present invention relates to a data compression and expansion method, a data compression and expansion device, a transmitter and receiver, a recording and reproducing device, and an audio signal recording medium.

Data compression of the audio signals is known, for example, from EP-A 402.973 (D1). This document describes a subband encoder in which the audio signal is A / D converted at a specific sampling rate, e.g. 44.1 kHz, and the obtained audio signal samples in the form of, for example, 24-bit words are fed to the subband separator filter. The subband splitter filter splits the wideband digital audio signal into a plurality of relatively narrowband subband signals. Using the psychoacoustic model, a masked threshold is obtained and the sample blocks of the subband signals are then quantized with a specific number of bits per sample for each block of subband signals in response to the masked threshold, resulting in significant data compression of the audio signal to be transmitted. The performed data compression is based on the "ejection" of those components in the audio signal that are inaudible, and therefore is a method of data compression with losses. The data compression described in document D1 is a rather intelligent method of data compression and requires a significant number of gates or instructions to be implemented in hardware or software, respectively, and thus is costly. Moreover, the subsequent expansion device also requires a significant number of gates or instructions in hardware or software implementation, respectively.

The essence of the invention is a method of data compression, for data compression of an audio signal, in which an audio signal is received, conversion is performed on the audio signal, obtaining a signal in the form of a 1-bit stream, lossless data compression is performed on a bit stream, obtaining a compressed data stream signal, and a compressed data bitstream signal is provided, characterized in that sigma-delta modulation is performed during the audio conversion, and during lossless data compression, entropy the bitstream signal is entropy-coded in response to a probability signal and the compressed data bitstream signal is obtained, then prediction is performed for the bitstream signal and a probability signal is determined for the output signal obtained in the prediction step.

Moreover, the method according to the invention is characterized in that when performing the prediction, a prediction filter operation is performed on the bitstream signal and a multivalued output signal is obtained, and a probability signal is further extracted from the multivalued output signal.

The invention also relates to a data expansion method for expanding a compressed audio signal to obtain a replica of the original audio signal, the compressed audio signal being a lossless compressed bit signal generated by the modulator. The method receives a compressed audio signal which is a compressed data bitstream signal, performs a lossless data expansion step on the compressed data bitstream signal, and produces a bitstream signal, performs D / A digital conversion for the bitstream signal to obtain a replica of the original audio signal, and then a replica of the original audio signal is provided, characterized by that a bitstream is generated with a sigma-delta modulator, and during lossless decoding, entropy decoding of the bitstream signal is performed in response to the probability signal, and a bitstream signal is obtained, and a probability signal is provided.

Moreover, the method according to the invention is characterized in that arithmetic decoding is performed during entropy decoding.

The invention further relates to a data compression device for compressing an audio signal, which comprises an input block for receiving an audio signal, a conversion block converting an audio signal into a 1-bit stream signal, a lossless encoding block performing a lossless encoding of a bitstream signal to obtain a bitstream signal. Compressed, the output block that provides the compressed data bitstream signal, characterized in that the conversion block is a sigma-delta modulator and the lossless compression block comprises an entropy encoder for entropy encoding the bitstream signal in response to the probability signal to obtain a data bitstream signal

Compressed, a prediction filter for performing a prediction step on the bitstream signal; and a probability signal determination block from the output signal outputted by the prediction filter.

Moreover, the device according to the invention is characterized in that the audio signal is an analog audio signal and the conversion block is an analog-to-digital A / D conversion block (60) performing 1-bit analog-to-digit A / D conversion on the analog audio signal to obtain a stream signal. bitwise.

Moreover, the apparatus according to the invention is characterized in that the prediction filter comprises means for performing predictive filtering on the bit stream signal to obtain a multi-valued output signal, and a probability signal derived from the multi-valued output signal is output from the probability signal determination block.

Moreover, the device according to the invention is characterized in that the entropy encoder is an arithmetic encoder.

The essence of the invention is a data expansion device for expanding the bitstream signal of compressed audio data to obtain a replica of the original audio signal. The compressed audio data bitstream signal has been obtained by lossless compression of the bitstream signal generated by the modulator, which device comprises an input block for receiving a compressed audio signal in the form of a compressed data bitstream signal, a lossless decoding block for performing a lossless data expansion of the compressed data bitstream signal for obtaining a bit stream, a digital-to-analog D / A conversion block for performing a digital-to-analog conversion of the bit stream to obtain a replica of the original audio signal, an output block for providing a replica of the original audio signal, characterized in that it is provided with a sigma-delta modulator for generating the bit stream, a lossless decoding block comprises an entropy decoder for entropy decoding a compressed data bitstream signal in response to a probability signal to obtain a bitstream signal and a probability signal generator for inputting a probability signal.

Moreover, the device according to the invention is characterized in that the entropy decoder is an arithmetic decoder.

Moreover, the device according to the invention is characterized in that the digital-analog D / A conversion block comprises a sigma-delta demodulator.

The invention also relates to an audio signal transmitter for transmitting an audio signal by means of a transmission medium, which transmitter is provided with a data expansion device comprising an input block for receiving an audio signal, an audio signal conversion block into a 1-bit stream signal, a lossless coding block of a bitstream signal into a compressed data bitstream signal and an output block for providing a compressed data bitstream signal, characterized in that the conversion block is a sigma-delta modulator, and the lossless compression block comprises an entropy coder for entropy coding of the bitstream signal in response to a probability signal for obtaining a compressed data bitstream signal, a prediction filter for performing a prediction step on the bitstream signal; and a probability signal determination block from the output signal output by the prediction filter. The audio signal is an analog audio signal and the conversion block is an analog-to-digital A / D conversion block performing 1-bit analog-to-digital A / D conversion on the analog audio signal to obtain a bitstream signal. The predictive filter includes means for performing predictive filtering on the bitstream signal to obtain a multi-valued output signal. At the output of the probability signal determination block, there is a probability signal derived from the multivalued output signal, wherein the entropy encoder is an arithmetic encoder, the transmitter further comprising a transmission block for providing a compressed bitstream signal to the transmission medium.

Furthermore, the inventive transmitter is characterized in that it is additionally provided with an error correction encoder and / or a channel encoder for error correction and / or channel encoding of the compressed data bitstream signal prior to providing the compressed data bitstream signal to the transmission medium.

The invention also relates to an audio signal receiver for receiving an audio signal via a transmission medium, which receiver is provided with a data expansion device for the compressed audio data bitstream signal, comprising an input block for receiving

Compressed audio signal, a lossless decoding block for lossless data expansion, a digital-analog D / A conversion block for replicating the original audio signal, and an output block providing a replica of the original audio signal, characterized in that a bit stream generation is provided with in a sigma-delta modulator, a lossless decoding block comprises an entropy decoder for entropy decoding a compressed data bitstream signal in response to a probability signal to obtain a bitstream signal and a probability signal generator for inputting a probability signal. The entropy decoder is an arithmetic decoder, and the D / A digital conversion block includes a sigma-delta demodulator, and the receiver includes a receiver block for receiving compressed data bitstream signal from the transmission medium.

Furthermore, the receiver according to the invention is characterized in that it further comprises a channel decoder and / or an error correction decoder for coding and / or channel coding error correction for a signal received from the transmission medium to obtain a compressed data bitstream signal.

The invention also relates to an audio signal recording device, on a recording medium, provided with a data compression device comprising an input block for receiving an audio signal, a block for converting an audio signal into a 1-bit stream signal, a block for encoding a lossless bit stream signal into a compressed data bit stream signal, and an output block providing a compressed data bitstream signal, characterized by that the conversion block is a sigma-delta modulator, and the lossless compression block comprises an entropy encoder for entropy coding of the bitstream signal in response to a probability signal to obtain a compressed data bitstream signal, a prediction filter for performing a prediction step on the bitstream signal, and a probability signal determination block from the output signal withdrawn by the predictive filter. The audio signal is an analog audio signal and the conversion block is an analog-to-digital A / D conversion block performing 1-bit analog-to-digital A / D conversion on the analog audio signal to obtain a bitstream signal. The predictive filter includes means for performing predictive filtering on the bitstream signal to obtain a multi-valued output signal. At the output of the probability signal determination block, there is a probability signal derived from the multivalued output signal, wherein the entropy encoder is an arithmetic encoder. The recording apparatus further comprises a recorder for recording the compressed data bit stream signal on the recording medium.

Moreover, the device according to the invention is characterized in that the recording medium is an optical or magnetic recording medium.

Moreover, the inventive apparatus is characterized in that it further comprises an error correction encoder and / or an error correction channel encoder for coding and / or channel coding of the compressed bitstream bitstream signal before recording the compressed data bitstream signal on the recording medium.

The invention also relates to a device for reproducing an audio signal from a recording medium, provided with a data expansion device of the compressed audio data bitstream signal, including an input block for receiving a compressed audio signal, a lossless decoding block for lossless data expansion, a D / A digital-to-analog conversion block. to obtain a replica of the original audio signal and an output block providing a replica of the original audio signal, characterized in that it is provided with a sigma-delta modulator for bitstream generation, and the lossless decoding block comprises an entropy decoder for entropy decoding a bitstream compressed data bitstream signal in response to a probability signal to obtain a bitstream signal and a probability signal generator for inputting a probability signal. The entropy decoder is an arithmetic decoder, and the D / A conversion block includes a sigma-delta demodulator, the reproduction apparatus further comprising a read block (70) for reading the compressed data bitstream signal from the track of the recording medium.

Moreover, the apparatus according to the invention is characterized in that it is provided with a channel decoder and / or an error correction decoder for error correction of the channel coding and / or the channel coding of the signal received from the transmission medium to obtain a compressed data bitstream signal.

PL 192 073 B1

The invention also relates to a recording medium having a compressed data bit stream signal recorded in a track arranged on the recording medium. The compressed data bitstream signal was obtained by performing lossless data compression on the 1-bit stream signal, and the 1-bit stream signal was obtained by performing the conversion of the audio signal, a medium characterized in that the conversion is sigma-delta modulation, and during lossless compression, entropy the bitstream signal is entropy-coded in response to a probability signal to obtain the compressed data bitstream signal, the bitstream signal is predicted, and a probability signal is determined for the output signal obtained in the prediction step.

According to the invention, a simpler data compression device for compressing audio data is provided and also provides a simpler and less costly construction of the corresponding expander device.

The data compression apparatus of the present invention has an input block for receiving an audio signal, a conversion block for converting the audio signal to a 1-bit stream, the audio conversion block comprising a sigma-delta modulation block, a lossless block. encoding to implement a lossless compression step on a signal in the form of a bitstream, for obtaining a compressed data stream signal; and an output block for outputting a compressed data stream signal, the conversion block being an A / D (analog-to-digital) conversion block for performing 1 bit conversion on an analog audio signal to obtain a stream signal bitwise.

The invention is based on the following diagnosis. The audio signal can be used in analog or digital form. In A / D conversion according to the present invention, an analog audio signal with a 1 bit A / D converter (also called a bit stream converter or a sigma-delta modulator), the audio signal to be converted to A / D is sampled at a frequency that is usually in multiples of 44.1 kHz or 48 kHz. The output signal of a 1-bit A / D converter is a binary signal, called a bit stream signal. When an audio signal is input in digital form, sampled at e.g. 44.1 kHz, and samples are expressed with e.g. 16 bits per sample, this digital signal is re-sampled at a frequency that is again a multiple of the sampling rate of 44. 1kHz (or 48kHz), resulting in a 1 bit stream signal.

Converting an audio signal to a 1 bit stream signal has numerous advantages. Bitstream conversion is a high quality encoding method with the possibility of high quality decoding or low quality decoding, with the further advantage of simplifying the decoding circuit.

Problems related to such solutions are presented in the publications: "A digital decimating filter for analog-to-digital conversion of hi-fi audio signals" / auto. JJ van der Kam, document D2 in the list of related documents, and "A higher order topology for interpolative modulators for oversampling A / D converters", aut. Kirk CH Chao et al. Document D3 in the list of related documents.

1-bit converters are used in CD players, for example, to re-convert an audio bitstream into an analog audio signal. However, the audio signal recorded on the CD is not a compressed 1-bit bit stream signal.

As is known, the resultant bitstream signal of a 1 bit A / D converter is generally considered a random signal with a "noise-like" frequency spectrum. These kinds of signals are difficult to compress data.

Surprisingly, however, it has been found that by using a lossless encoder such as a variable length encoder such as a Huffman encoder or an arithmetic encoder, a significant data reduction can be achieved despite the noise-like nature of the bitstream signal from the 1 bit A / D converter. .

The subject of the invention is explained in more detail in the drawing, in which Fig. 1 shows a diagram of a data compression device, Fig. 2A - frequency spectrum of the output signal of the 1-bit A / D converter, Fig. 2B - frequency spectrum of the same sy6

Fig. 3 - data compression device included in a bitstream signal recording device with data compression on a record carrier, Fig. 4 - data compression device in a transmitting device for transmitting the stream signal 5 is a schematic diagram of one embodiment of the data expansion device, fig. 6 - data expansion device included in a data compression bitstream signal recovery device from a recording medium, fig. 7 - diagram of a data expansion device included in the receiving device for receiving a bitstream signal compressed data from a transmission medium, fig. 8 - diagram of a further embodiment of the recording device, additionally equipped with an error correction encoder and a channel encoder, Fig. 9 - diagram of a further embodiment of the reproduction apparatus, further provided with an error correction decoder and a channel decoder, Fig. 10 - diagram of a data compression apparatus, in which a lossless encoder is in the form of an arithmetic encoder, and Fig. 11 is a diagram of a different embodiment of the data expansion apparatus, wherein the lossless decoder is an arithmetic encoder.

Fig. 1 shows an embodiment of a data compression device including an input terminal 1 for receiving an audio signal. In this example, the audio signal is an analog audio signal. Input terminal 1 is connected to input 2 of a 1-bit A / D converter in the form of a conversion block 4, which is preferably a sigmadelta modulator. The output 6 of the 1 bit A / D converter in the form of the conversion block 4 is connected to the input 8 of the lossless encoding block 10 with data compression. The output 12 of the data compression lossless encoding block 10 is connected to the output terminal 14.

This conversion block 4 is adapted to perform 1-bit analog-to-digital conversion on the signal to obtain a bitstream signal which is fed to the output 6.

For this purpose, the conversion block 4 receives a sampling rate equal to Nf_s, via input 16. The magnitude fs is a frequency with a value of e.g. 32 kHz, 44.1 or 48 kHz and N is a large integer, e.g. 64. The audio signal is sampled in the conversion block 4 with a sampling frequency of e.g. 2.8224 MHz (64x44.1 kHz). The bitstream signal appears at the output 6 of the A / D converter with a sampling frequency of, for example, 2.8224 MHz (64x44.1 kHz). The bitstream signal appearing at the output 6 of the conversion block 4 is a bit rate of 2.8224 MHz.

The lossless encoder 10 takes the form of a data compressed encoder. Lossless encoders have the advantage that they can compress data of the audio signal such that after expanding the data in a lossless decoder, it is possible to substantially reconstruct the original signal. This means that, in principle, there is no loss of information after compression / expansion. Lossless encoders may be in the form of a variable length encoder. Variable length encoders are known. Examples of such variable length coders are Hufmann coders, arithmetic coders and Lem-pela-Ziva coders. In this regard, reference is made to the publication "A metod for the construction of minimum-redundacy codes" aut. DAHuffmann, Document D4 in Related Documents List, "An introduction to arithmetic coding" aut. GG Langdon, Document D5 in List of Related Documents, and "A universal algorithm for sequential data compression", by J. Ziviin., Document D6 in List of Related Documents.

The lossless encoding block 10 performs a substantially lossless data compression step on the bitstream signal to obtain the data compressed bitstream signal at its output 12, which is applied to output terminal 14.

Nafig. 2A shows the frequency spectrum of the bitstream signal present at the output 6 of the A / D converter in the form of a conversion block 4, for the input signal in the form of a 5 kHz sine wave, sampled at the frequency of 2.8224 MHz. The spectrum therefore represents frequencies between 0Hza1.4 MHz. Fig. 2B shows a portion of the spectrum shown in Fig. 2A, namely the portion between 0Hz100kHz, to more clearly represent the 5kHz sine wave contained in the bitstream signal. The noise-like nature of the bitstream signal is clearly visible, especially in the higher frequency area, which seems to mean that data compression on this signal will not result in a significant data reduction.

Contrary to this, studies have shown that data reduction can be achieved. The table below shows the results of data compression performed by three lossless encoders for three different musical fragments:

PL 192 073 B1

<td rowspan="2">fragment</td><td colspan="3">d</td>

<td>Huffman (8b)</td><td>Huffman (16b)</td><td>Lempel-Ziv</td>

<td>bossanova</td><td> 1,31</td><td> 1,45</td><td> 1,73</td>

<td>jazz</td><td> 1,35</td><td> 1,50</td><td> 1,77</td>

<td>Classical music</td><td> 1,38</td><td> 1,59</td><td> 1,86</td>

where d is the compression rate defined as the ratio of the bit rate of the encoder input to the bit rate of the encoder output.

Fig. 3 shows an embodiment of an apparatus including the data compression apparatus shown in Fig. 1. The recording apparatus furthermore comprises a recorder 30 for recording data of the compressed bitstream signal in a track of the recording medium 32. In the present example, the recording medium 32 is a magnetic recording medium, such that the recording block 30 includes at least one magnetic head 34 for recording data of a compressed bitstream signal on the recording medium 32. However, the recording medium may be an optical recording medium, such as a CD or DVD.

Fig. 4 shows an alternative embodiment of a transmitter for transmitting an audio signal through a TRM transmission medium comprising a data compression device as shown in Fig. 1. The transmitter further comprises a transmission block 40 for inputting a bitstream bitstream signal with data compression into the TRM transmission medium . Transmission unit 40 may include an antenna 42.

Transmission via a transmission medium, e.g., a radio link or a recording medium, typically requires error correction coding performed on the data compressed bitstream signal to be transmitted. Fig. 8 shows such signal processing steps performed on the data compressed bitstream signal in the case of the recorder of Fig. 3. The recorder of FIG. 8 thus includes an error correction encoder (ERCO) 80 as known in the art and a channel encoder 82 also known.

Fig. 5 shows an alternative embodiment of a data expansion device. The apparatus includes an input terminal 50 for receiving a data compressed audio signal which is a data compressed bitstream signal provided by the data compression apparatus of Fig. 1. Input terminal 50 is connected to input 52 of data expansion block 54, which has an output 56 connected to input 58 of conversion block 60. The output 62 of the conversion block 60 is connected to the output terminal 64.

Lossless decoding block 54 is a data expansion block, for example a variable length decoder in the form of, for example, a Huffman decoder or an arithmetic decoder. It is evident that the decoder in the data expansion device of fig. 5 should be the inverse of the encoder used in the data compression device of fig. 1 for a substantially lossless performance of the encoding-decoding step. The data expansion lossless decoding block 54 develops the data compressed bitstream to obtain a replica of the original bitstream that is fed to input 58 of the D / A converter as a conversion block 60 that converts this bitstream into an analog audio signal that it is fed to terminal 64.

Fig. 6 shows the data expansion device of Fig. 5 included in the playback device. The reproduction apparatus further comprises a read block 70 for reading a compressed bitstream signal from the track of the recording medium 32. In the example shown, the recording medium is a magnetic recording medium, such that the recording block 70 comprises at least one magnetic head 72 for reading the data of the compressed bitstream signal. from a recording medium 32. The recording medium, however, may be an optical recording medium, such as, for example, a CD or a DVD.

Fig. 7 shows an alternative embodiment of a receiver for receiving an audio signal through a TRM transmission medium, including a data expansion device as shown in Fig. 5. The receiver further comprises a receiver block 75 for receiving a bitstream signal compressed data from the TRM transmission medium. . Receiving block 75 may include an antenna 77.

As already explained, transmission via a transmission medium such as a radio link or a recording medium typically requires error correction coding performed on the data compressed bitstream signal to be transmitted, such that upon reception it can be

Corresponding channel decoding and error correction decoding must be performed. Fig. 9 shows such channel decoding and error correction processing steps of the signal performed on the received signal received by reading block 70 in the case of the reproducer circuit of FIG. 6. The reproduction circuit of Fig. 9 thus it comprises a channel decoder 90, known in the art, and an error correction decoder 92, also known to obtain a replica of the compressed data bit stream signal.

Another data compression device is shown in Fig. 10. In the data compression device of Fig. 10, the data stream signal is provided to input 8 of a lossless encoder in the form of an entropy encoder 154, for example an arithmetic encoder. In addition, the bitstream signal is also input to the probability signal determination block 156. The arithmetic encoder encodes the bitstream signal into a data compressed bitstream signal in response to the probability p values ​​supplied to its input 192. The probability signal determination unit 156 determines a probability value indicating the probability that the bit in the bit stream provided by the conversion block 4 has a predetermined value. logical, for example "1". This probability value, marked in Fig. 10 as p, is provided to the entropy encoder 154. The determination block 156 determines this probability value from the output of the prediction filter 152. The entropy encoder 154 may perform bitstream data compression on a frame-by-frame basis.

The device of Fig. 10 operates as follows. The predictive filter 152 performs the predictive filtering on the bitstream signal to output a multi-bit signal. The multi-bit signal has multiple levels ranging from, for example, +3 to -3. In addition, for each of the subinterval sets in the range of the value of the multi-bit output signal, it is determined what the probability is that the corresponding bit in the bitstream signal is, for example, a "1" bit. This may be accomplished by counting "ones" and "zeros" present in the signal bitstream during a predetermined period of time when the multi-bit output signal falls within one of these ranges. The resulting probabilities for different values ​​of the multi-bit output signal are then reported as the probability signal p to the arithmetic entropy encoder 154. The data compressed bitstream signal is provided by an entropy encoder 154 to an output line 158 for transmission via the TRM transmission medium or the recording medium.

Fig. 11 shows an expansion device for decoding a data compressed bitstream signal received via the TRM transmission medium. The data processing apparatus of FIG. 11 includes an entropy decoder 172 that receives a data compressed bitstream signal through input 174. In the illustrated example, an entropy decoder 172 into the form of an arithmetic decoder that performs the arithmetic decoding step on the data compressed bitstream signal data under the influence of a probability signal p applied to input 176 to generate a replica of the original bitstream signal that is provided to output 178. is applied to the input 58 of the D / A conversion block 60.

In addition, a probability determination block is used to feed the probability signal p to the arithmetic entropy decoder 172. The probability signal p may be obtained in various ways depending on how the probability signal was determined at the encoder. One approach is to extract the signal adaptively from the output of the prediction filter 181. In this embodiment, the prediction filter 181 is equivalent to the prediction filter 152 at the encoder and the probability signal generator 180 is equivalent to the probability determination block 156 at the encoder of FIG. 10. Another method of generating the probability signal p is to use side information obtained via the transmission medium TRM. as will be explained below.

The side information may be generated by the transmission apparatus of Fig. 10 and passed to the apparatus of Fig. 11. Such side information preferably comprises prediction filter coefficients 152, which are determined on a sequential-frame basis, the coefficients being transmitted to the corresponding prediction filter included in the Fig. in a probability signal generator 180.

In addition, the apparatus of FIG. 10 can generate parameters describing the conversion of the multi-bit output from the prediction filter 152 into the probability signal p. Such parameters are also included in side information and transmitted to the probability signal generator 180 and the prediction filter 181, so as to allow regeneration of the signal. the probability p in the device of fig. 11 based on the multi-bit output provided by the predictive filter 181.

The entropy encoder used in the embodiment of fig. 10 is adapted to encode the bitstream signal with the probability signal to obtain the data compressed bitstream signal. One such entropy coder is the arithmetic coder described above. One of the other types of entropy coders is, for example, the known finite state coder. The entropy decoder used in the embodiment of fig. 11 is operable to decode the data compressed bitstream signal with a probability signal to obtain a replica of the bitstream signal. One such entropy decoder is the arithmetic decoder described above. One other type of entropy decoder is, for example, the known finite state decoder.

While the invention has been described with reference to its preferred embodiments, these examples are not limiting. Thus, various modifications are possible without departing from the scope of the invention as defined in the claims. When the audio signal is provided in digital form, for example as a signal sampled at 44.1 kHz, and the samples are expressed in, for example, 16 bits, the conversion means are adapted to resample the digital audio signal at a frequency of, for example, 64 × 44.1 kHz, for receiving a 1 bit stream signal

Furthermore, it should be noted that the invention also applies to an embodiment in which the bit stream signal provided by the converter 4 is subjected to an additional signal processing step resulting in a processed 1 bit signal which is fed to the encoding block. lossless 10. This additional signal processing step may include combining the left and right stereo components as a 1 bit stream into a processed 1 bit bit stream signal.