GB2314198A - Digital audio data recording format compatible with differing sample frequencies - Google Patents

Abstract

Disclosed is a digital audio recording apparatus for formatting digital audio data and recording formatted data on a digital recording medium, so that digital audio data having a first sampling frequency and other digital audio data having a second sampling frequency being twice the first sampling frequency can be reproduced in both a reproduction apparatus having an operating frequency for digital-to-analog converting the first sampling frequency and that having an operating frequency for digital-to-analog converting the second sampling frequency. The digital audio recording apparatus transforms the digital audio data into transformation coefficients in a frequency domain, the transformation coefficients are formatted using one of predetermined recording formats. Corresponding digital audio reproduction apparatus reproduces an analog audio signal from the formatted data, based on an operating frequency for D/A conversion, a formatting method of the formatted data, and a sampling frequency of the audio signal contained in the formatted data.

Description

SYSTEM FOR RECORDING AND/OR REPRODUCING A PULSE CODE MODULATION DIGITAL AUDIO SIGNAL The present invention relates to a system for recording and/or reproducing a pulse code modulation (PCM) digital audio signal, and more particularly, to a system for recording and/or reproducing a PCM digital audio signal, in which digital audio signals can be recorded on a digital recording medium or can be reproduced from the digital recording medium, even though sampling frequencies of the PCM digital audio signals differ from each other.

All apparatuses which use PCM digital audio signals, use a reference unit which is a data unit for enabling an error correction. The size of the reference unit is determined according to the features of a transmission medium. A digital audio signal which has been sampled according to a predetermined sampling frequency is recorded on a recording medium, in the form of blocks having a size or amount of data which is determined according to a data recording characteristic of the recording medium, such as a compact disk (CD), a digital audio tape (DAT) and so on. When a reproduction operation is performed with respect to the recording medium, a digital-toanalog converter converts a digital audio signal into an analog audio signal in the sequence of the outflow of the data from the recording medium.

As to PCM digital audio signals, in order to replace an existing system which uses a sampling frequency of 44.1 HKz or 48KHz, new audio recording systems which use a sampling frequency of 88.2KHz or 96KHz, for example, an advanced audio (ADA) system in Japan, have been proposed. However, the existing reproduction system which uses the sampling frequency of 44.1KHz or 48KHz, cannot reproduce audio signals which have been recorded in a digital form according to the newly proposed systems. Therefore, in order to make such an existing reproducing system reproduce a digital audio signal which has been recorded according to a new recording system, a separate digital signal processing is required so that a bit number representing each sample without creating noise can be handled. Among examples of the required digital signal processing, there is a low-pass filtering to eradicate a frequency component higher than 44.1KHz or 48KHz from a signal read from a recording medium, a decimation filtering to make the low-pass filtered signal into a signal having the sampling frequency of 44.1KHz or 48KHz.

For this reason, the existing reproduction system should process all input audio data in order to reproduce an audio signal according to the newly proposed system. Consequently, a digital processor having an operating frequency larger than a sampling frequency of the input audio data, is required. Thus, it costs too high to improve the existing reproducing system in order to reproduce a digital audio signal of a proposed signal recording system. Also, an amount of RAM capacity is additionally required for the above-described separate digital signal processing, thereby increasing the costs necessary for such an improvement.

Meanwhile, a reproducing system which includes a digital-to-analog converter having a sampling frequency of 88.2KHz or 96KHz, directly transmits received data to an output terminal without processing the received data. Thus, a digital processor for processing audio data and a large amount of RAM capacity are not required. However, if another audio recording system using a frequency higher than 88.2KHz (or 96KHz) is proposed, the same problems as those of existing system are caused.

With a view to solve or reduce the above problems, it is an aim of embodiments of the present invention to provide a system for recording audio signals sampled according to an existing recording method and a new recording method in both an existing audio apparatus and a new audio apparatus employing the new recording method, by converting audio samples within a predetermined reference unit of a digital audio signal into transformation coefficient of a frequency domain and formatting the transformation coefficients according to a predetermined recording format.

Another aim of embodiments of the invention is to provide a system for reproducing audio signals sampled according to an existing recording method and a new recording method in both an existing audio apparatus and a new audio apparatus employing the new recording method, by converting audio samples within a predetermined reference unit of a digital audio signal into transformation coefficients of a frequency domain and formatting the transformation coefficients according to a predetermined recording format.

According to a first aspect of the present invention, there is provided a digital audio recording apparatus for a digital recording medium, the digital audio recording apparatus comprising: reference unit formation means for receiving a pulse-code-modulated digital audio signal, and forming a sequence of reference units each reference unit having a predetermined size from the received digital audio signal; transformation means for receiving the sequence of reference units, for transforming audio samples belonging to an individual reference unit into transformation coefficients in a frequency domain, and outputting a reference unit sequence containing transformation coefficients; formatting means for receiving the reference unit sequence from the transformation means, and formatting and outputting the received reference unit sequence, using one of a first recording format and a second recording format, wherein the first recording format is for forming a first recording unit containing transformation coefficients belonging to respective reference unit, the second recording format is for forming both a second recording unit containing transformation coefficients belonging to a lower frequency area and a third recording unit containing transformation coefficients belonging to a higher frequency area among transformation coefficients contained in respective reference unit; and recording means for recording the recording unit sequence output from the formatting means on the digital recording medium.

Preferably, said lower frequency area and said higher frequency area are bisected from a frequency band represented by transformation coefficients.

Said predetermined size may be determined based on an audio data amount of which an error imposed during recording and reproducing a linear pulse-code-modulated digital audio signal can be corrected.

The recording unit is preferably determine based on a data amount which can be continuously recorded on a digital recording medium according to a signal recording characteristic of the digital recording medium.

Said formatting means may further comprise an additional data inserter for inserting additional data representing the sampling frequency of the audio signal which is contained in the recording unit sequence with regard to a sequence of the first recording units produced by using the first recording format, into the recording unit sequence.

Said additional data inserter may further insert additional data representing the number of audio samples in an individual recording unit into the recording unit sequence.

Said formatting means preferably comprises an additional data inserter for inserting a first additional data representing a sampling frequency of the audio signal contained in a recording unit sequence into the recording unit sequence, and inserting a second additional data which discerns the first recording unit and the second recording unit obtained from the same reference unit, into the preceding end of each of the first and second recording units, with regard to the recording unit sequence produced by using the second recording format.

Said formatting means preferably further inserts the recording format data for discerning the first recording format and the second recording format into said recording unit sequence.

According to a further aspect of the invention, there is provided a digital audio reproduction apparatus comprising: an input end for receiving data formatted by using one of a first recording format and a second recording format, wherein the first recording format is for forming a first recording unit containing transformation coefficients belonging to each reference unit, and the second recording format is for forming a second recording unit containing transformation coefficients in a lower frequency area and a third recording unit containing transformation coefficients in a higher frequency area among transformation coefficients contained in each reference unit; a digital-to-analog (D/A) converter for digital-to-analog converting an input digital audio signal according to a predetermined operating frequency; means, coupled to the input end, for discriminating sampling frequency of the audio signal contained in the input formatted data and, a recording format, and outputting data representing the discrimination result; inverse formatting means, coupled to the input end and receiving data output from means for discriminating, for inversely formatting the formatted data received according to comparison between the discriminated sampling frequency and the predetermined operating frequency, and the discriminated recording format of the prestored first and second recording formats; and inverse transformation means having an inverse transformation characteristic optimized to the D/A converter, for transforming the transformation coefficients output from the inverse formatting means into audio samples in a temporal domain, and supplying resultant audio samples to the D/A Converter.

Preferably, said input end receives said formatted data from the digital recording medium.

Said each recording unit is preferably determined based on a data amount which can be continuously recorded on said digital recording medium according to a signal recording characteristic of the digital recording medium.

Said lower frequency area and said higher frequency area are preferably bisected from the whole frequency area represented by transformation coefficients.

Preferably, said inverse formatting means supplies to said inverse transformation means the transformation coefficients of the lower frequency area among transformation coefficients contained in the first recording unit, in the case that the discriminated sampling frequency is said predetermined operating frequency multiplies by factors of two, and the discriminated recording format is the first recording format.

Preferably said inverse formatting means supplies the transformation coefficients contained in the second recording unit to said inverse transformation means, in the case that the discriminated sampling frequency is said predetermined operating frequency multiplied by factors of two, and the discriminated recording format is the second recording format.

Preferably, said inverse formatting means supplies all transformation coefficients to said inverse transformation means when said predetermined operating frequency is the discriminated sampling frequency multiplied by factors of two, and said inverse transformation means performs zero padding for every reference unit prior to inversely transforming the transformation coefficients received from said inverse transformation means.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 is a schematic block diagram of a digital audio recording apparatus according to a preferred embodiment of the present invention; Figure 2 is a detailed block diagram of a formatting unit shown in Figure 1; Figures 3A through 3D are views for explaining recording formats according to embodiments of the present invention; Figure 4 is a schematic block diagram of a digital audio reproduction apparatus according to an embodiment of the present invention; and Figure 5 is a block diagram of a digital audio reproduction apparatus according to an embodiment of the present invention.

Preferred embodiments of the present invention will be described below in more detail with reference to the accompanying drawings.

A digital audio signal recording apparatus according to the present invention shown in Figure 1, can record an audio signal having a sampling frequency of 44.1KHz or 48KHz according to an existing audio recording method as well as an audio signal having a sampling frequency of 88.2KHz or 96KHz according to a new audio recording method, on a recording medium according to a proposed recording format. For clarity of explanation, a relatively higher sampling frequency is called a first sampling frequency, and a relatively lower sampling frequency is called a second sampling frequency.

An audio signal sampled in a temporal domain which is quantized using a linear PCM is input to a reference unit former 10 of Figure 1. The reference unit former 10 divides the input digital audio signal into reference units each having a predetermined size. The reference unit and the recording unit to be described are determined by an audio quality and the characteristic of the transmission medium. In other words, a size of the reference unit is determined based on a data amount of which the error imposed during recording and reproduction of linear pulse-code-modulated digital audio signal can be corrected. A size of the recording unit is determined based on a data amount which can be continuously recorded on or read out from a digital recording medium according to a signal recording characteristic of the digital recording medium. An example of the reference unit obtained by division is shown in Figure 3A. The reference unit of Figure 3A is composed of a sequence of 2m audio samples. The reference unit former 10 supplies the reference units obtained by division to a transformer 20 sequentially. The transformer 20 transforms the audio samples into transformation coefficients in a frequency domain. The capability of the transformer 20 is determined by the audio quality of a target audio signal. The transformation coefficients obtained by the domain transformation of the individual reference units are output to the formatting unit 30 in the form of being discerned for each reference unit. The formatting unit 30 formats transformation coefficients in each reference unit, by using one of a first recording format illustrated in Figure 3B, and a second recording format illustrated in Figures 3C and 3D.

The detailed construction and the operation of the formatting unit 30 will be described in detail with reference to Figure 2 and Figures 3B through 3D.

The recorder 40 digitally records the data formatted in the formatting unit 30 on a digital recording medium (not shown) such as a CD and a DAT.

Referring to Figure 2 showing a detailed block diagram of the formatting unit 30, a recording format designator 32 in the formatting unit 30 designates one of a first and a second recording formats with respect to the reference units obtained in the reference unit former 10. The recording format designation of the recording format designator 32 can be accomplished by a user who intends to record an audio signal, by design.

When a first recording format is selected, the recording format designator 32 outputs a sequence of the transformation coefficients which are received from the transformer 20 to a first data formatter 34. The first data formatter 34 formats audio samples within an individual reference unit into a first recording unit and outputs a sequence of the first recording units to a first additional data inserter 35. The first recording unit includes transformation coefficients obtained from one reference unit.

Figure 3B shows transformation coefficients F[0], F[1], F[2], . .., and F[2m] contained in a first recording unit. In Figure 3B, F[0] represents the transformation coefficient of the lowest frequency, and F[2m] represents the transformation coefficient of the highest frequency. The first additional data inserter 35 inserts first additional data representing a sampling frequency of the audio signal contained in the received recording unit sequence and second additional data representing the number of the audio samples in an individual recording unit, into the preceding end of the recording unit sequence. Since the present invention is not limited to the example where the first and second additional data is inserted into the preceding end of the recording unit sequence, it is apparent to a person skilled in the art that the first data formatter 34 may be modified in such a manner that the first and second additional data can be properly inserted in the recording unit sequence according to the characteristic of a transmission channel or a recording medium.

When a second recording format is selected, the recording format designator 32 outputs a sequence of the reference units which are received from the transformer 20 to a second data formatter 36. The second data formatter 36 formats the transformation coefficients within an individual reference unit applied from the recording format designator 32 into two recording units. In more detail, the second data formatter 36 bisects the transformation coefficients in the reference unit, and forms a second recording unit composed of transformation coefficients in relatively lower frequency area and a third recording unit composed of transformation coefficients in the relatively higher frequency area. Therefore, two recording units are obtained from a reference unit. Figure 3C shows transformation coefficients F[0], F[1], F[2], ..., and F[m] contained in the second recording unit. Figure 3D shows transformation coefficients F[m], F[m+l], F[m+2], ..., and F[2m] contained in the third recording unit. The second data formatter 36 outputs a sequence of recording units obtained from a sequence of reference units to a second additional data inserter 37. In the sequence of the recording units, the second and third recording units corresponding to a relatively time-leading reference unit time-leads those corresponding to a relatively time-lagging reference unit. In case of the recording units corresponding to the same reference unit, the second recording unit time-leads the third recording unit.

The second additional data inserter 37 receives a sequence of the recording units from the second data formatter 36 and inserts the first additional data into the preceding end of the recording unit sequence output from the second data formatter 36. Also, the second additional data inserter 37 inserts third additional data for discerning second and third recording units obtained from the said reference unit into the preceding end of the respective preceding ends of second and third recording units.

The above-described apparatus of Figure 1 may use the two recording formats. However, it is desirable that only one recording format is used in an actual embodiment thereof. If the figure 1 apparatus uses both recording formats, separate additional data for discerning the two recording formats, that is, recording format data is needed. In this case, the recorder 40 in the Figure 1 apparatus inserts the recording format data in the preceding end of the formatted data.

The Figure 4 reproducing apparatus which reproduces a digital audio signal from a recording medium (not shown) on which the digital audio signal is recorded, includes a D/A converter 81 having the same operating frequency as the second sampling frequency. A reader 50 reads formatted data from the recording medium (not shown) on which the digital audio signal which is transformed into a frequency domain is recorded. The audio signal contained in the formatted data may have a first sampling frequency or a second sampling frequency as described above. A frequency discriminator 51 in the reader 50 discriminates a sampling frequency of digital audio signal based on first additional data contained in the read formatted data, and outputs the discriminated result to a recording format discriminator 53. The recording format discriminator 53 uses additional data which is contained in the formatted data received from the frequency discriminator 51 to discriminate the recording format of the formatted data. If the signal recorded on the recording medium is data formatted according to a first recording format, the data contains first and second additional data and recording format data. If the signal recorded on the recording medium is data formatted according to a second recording format, the data contains first and third additional data and recording format data. The reader 50 supplies one of the second and the third additional data and the sequence of the recording units based on the frequency discrimination result and the discriminated recording format to the inverse formatting unit 60(1). For data supply, it can be designed that the reader 50 supplies all the data read from the recording medium to the inverse formatting unit 60(1), and the inverse formatting unit 60(1) discriminates the sampling frequency and the recording format based on the received data from the reader 50 and selectively supplies audio data to an inverse transformer 71.

When the data recorded on the recording medium has a first sampling frequency and a first recording format, the inverse formatting unit 60(1) supplies the data received from the reader 50 to a first data extractor 61. The first data extractor 61 extracts the transformation coefficients in the low frequency area for every first recording unit of the data received from the reader 50. In more detail, the first data extractor 61 extracts the transformation coefficients of the low frequency area from the transformation coefficients in the individual recording unit based on the second additional data contained in the data received from the reader 50 and cancels the second additional data from the received data. Here, the low frequency area means a lower frequency area of the two frequency areas which are bisected from the whole frequency area represented by all transformation coefficients in an individual first recording unit. As a result, the individual first recording unit data output from the reader 50 is decimated by two to one (2 1) by means of the first data extractor 61. When the data recorded on the recording medium has a first sampling frequency and a second recording format, the inverse formatting unit 60(1) supplies the data received from the reader 50 to the first data extractor 61. The first data extractor 61 extracts the second recording units based on the third additional data contained in the data received from the reader 50, and cancels the third additional data. When the data recorded on the recording medium has a second sampling frequency and a first recording format, the inverse formatting unit 60(1) cancels the second additional data contained the data received from the reader 50. When the data recorded on the recording medium has a second sampling frequency and a second recording format, the first inverse formatting unit 60(1) supplies the data received from the reader 50 to a first inverse formatter 63. The first inverse formatter 63 inversely formats the second and the third recording unit corresponding to the same reference unit based on the prestored second recording format and the third additional data. Then, the first inverse formatter 63 cancels the third additional data and outputs the finally remained transformation in the above signal processing to the inverse transformer 71.

Since the present invention is not limited to the example where the first data extractor 61 and the first inverse formatter 63 cancel the second and/or third additional data, it is apparent to a person skilled in the art to modify the inverse formatting unit 60(1) to cancel the second and third additional data.

Also it is apparent to a person skilled in the art that the reader 50 may output all the data read from the recording medium to the inverse formatting unit 60(1), and the inverse formatting unit 60(1) cancels the recording format data among the data received from the reader 50.

The inverse transformer 71 which is adequately designed to inversely transform transformation coefficients of an individual reference unit obtained from the audio samples having a second sampling frequency, inversely transforms transformation coefficients received from the inverse formatting unit 60(1) into audio samples in a temporal domain. The audio samples output from the inverse transformer 71 are digital-to-analog converted in the D/A converter 81. The Figure 4 apparatus can reproduce an audio signal having a sampling frequency corresponding to twice that of an operating frequency of the D/A converter 81 as well as an audio signal having a sampling frequency corresponding to an operating frequency of the D/A converter 81. Thus, when the audio signal recorded on the recording medium has a first sampling frequency and the D/A converter 81 operates according to a second sampling frequency, the Figure 4 apparatus can provide an audio signal having the same audio quality which is not discriminated by the human auditory system.

Differently from the Figure 4 apparatus, Figure 5 shows a reproduction apparatus including a D/A converter 83 having the same operating frequency as a first sampling frequency. In Figure 5, since the blocks having the same reference numerals as those of Figure 4 perform the same functions as those of Figure 4 the detailed description thereof will be omitted. An inverse formatting unit 60(2) performs an inverse formatting operation with respect to a formatted data, using the data received from the reader 50. When the data recorded on the recording medium has a first sampling frequency and a first recording format, the inverse formatting unit 60(2) supplies the data received from the reader 50 to a second data extractor 65. The second data extractor 65 extracts the first recording units contained in the data received from the reader 50 and the cancels the second additional data. Thereafter, the inverse formatting unit 60(2) outputs the frequency discrimination result and the first recording units to an inverse transformer 73. The inverse transformer 73 determines that the currently received first recording units has the same sampling frequency as a sampling frequency in the D/A converter 83, based on the frequency discrimination result, and transforms transformations coefficients contained in the individual first recording unit into audio samples in a time domain. When the data recorded on the recording medium has a second sampling frequency and a first recording format, the second data extractor 65 in the inverse formatting unit 60(2) cancels the second additional data contained in the data received from the reader 50 and outputs the first recording units and the frequency discrimination result to the inverse transformer 73. In this case, if the transformation coefficients belonging to the first recording unit are transformed into the audio samples of the temporal domain, the number of the audio samples becomes smaller than that of the audio samples belonging to the reference unit relating to the signal processing of the Figure 5 apparatus. For this reason, the data padding unit 75 in the inverse transformer 73 performs zero padding to fill the data in the frequency domain. The inverse transformer 73 transforms the zeropadded transformation coefficients of the first recording unit into the audio samples in the temporal domain.

When the data recorded on a recording medium has a first sampling frequency and a second recording format, a second inverse formatter 67 in the inverse formatting unit 60(2) inversely formats the data received from the reader 50 according to a prestored second recording format. In more detail, the second inverse formatter 67 inversely formats the second and third recording units both of which corresponds to the same reference unit into a corresponding reference unit on the basis of the third additional data and the second recording format. Thereafter, the inverse formatting unit 60(2) cancels the third additional data and the recording format data, and outputs a sequence of the reference units and a frequency discrimination result to the inverse transformer 73. The inverse transformer 73 transforms the transformation coefficients of each reference unit into the audio samples of the temporal domain, based on the frequency discrimination result received from the inverse formatting unit 60(2).

When the data recorded on the recording medium has a second sampling frequency and a second recording format, the second inverse formatter 67 inversely formats the second and third recording units received from the reader 50 according to the third additional data and the prestored second recording format. In this case, the number of the audio samples in the temporal domain becomes smaller than that of the audio samples which are required for the signal processing in the Figure 5 apparatus. The data padding unit 135 performs the above-described zero-padding, and the resultant reference units are transformed into the audio samples of the temporal domain in the inverse transformer 133. These audio samples are digital-to-analog converted in the D/A converter 143. Thus, the Figure 5 apparatus can provide a digital audio signal having the existing sampling frequency to a listener as an acoustic

In this case, the transformation coefficients having the number obtained by the above formula are transformed into the audio samples of the temporal domain.

Using this concept, the system can be applied to an audio apparatus where a sampling frequency of an audio signal increases to an integer multiple of the first sampling frequency.

The above embodiments have been described in connection with the first and second sampling frequencies. However, the methods of present invention can be applied to an audio signal having a sampling frequency larger than the first sampling frequency.

As described above, the audio signal recording and reproduction system can reproduce audio signals having a two-times frequency difference between the sampling frequencies in the audio apparatus having a relatively lower sampling frequency and an audio apparatus having a relatively higher sampling frequency.

Also, audio signals having the different sampling frequencies can be reproduced in the audio apparatus having a relatively lower sampling frequency and an audio apparatus having a relatively higher sampling frequency. In addition, the present invention can be further applied to an audio apparatus adopting a new sampling frequency which increases at an integer multiple.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (18)

1. A digital audio recording apparatus for a digital recording medium, the digital audio recording apparatus comprising: reference unit formation means for receiving a pulse-code-modulated digital audio signal, and forming a sequence of reference units each reference unit having a predetermined size from the received digital audio signal; transformation means for receiving the sequence of reference units, transforming audio samples belonging to an individual reference unit into transformation coefficients in a frequency domain, and outputting a reference unit sequence containing transformation coefficients; formatting means for receiving the reference unit sequence from said transformation means, and formatting and outputting the received reference unit sequence, using one of a first recording format and a second recording format, wherein the first recording format is for forming a first recording unit containing transformation coefficients belonging to respective reference unit, the second recording format is for forming both a second recording unit containing transformation coefficients belonging to a lower frequency area and a third recording unit containing transformation coefficients belonging to a higher frequency area among transformation coefficients contained in respective reference unit; and recording means for recording the recording unit sequence output from said formatting means on the digital recording medium.

2. The digital audio recording apparatus according to claim 1, wherein said lower frequency area and said higher frequency area are bisected from a frequency band represented by transformation coefficients.

3. The digital audio recording apparatus according to claim 1 or 2, wherein said predetermined size is determined based on an audio data amount of which an error imposed during recording and reproducing a linear pulsecode-modulated digital audio signal can be corrected.

4. The digital audio recording apparatus according to claim 1, 2 or 3 wherein the recording unit is determined based on a data amount which can be continuously recorded on a digital recording medium according to a signal recording characteristic of the digital recording medium.

5. The digital audio recording apparatus according to claim 1, 2, 3 or 4 wherein said formatting means further comprises an additional data inserter for inserting additional data representing the sampling frequency of the audio signal which is contained in the recording unit sequence with regard to a sequence of the first recording units produced by using the first recording format, into the recording unit sequence.

6. The digital audio recording apparatus according to claim 5, wherein said additional data inserter further inserts additional data representing the number of audio samples in an individual recording unit into the recording unit sequence.

7. The digital audio recording apparatus according to claim 1, wherein said formatting means comprises an additional data inserter for inserting a first additional data representing a sampling frequency of the audio signal contained in a recording unit sequence into the recording unit sequence, and inserting a second additional data which discerns the first recording unit and the second recording unit obtained from the same reference unit, into the preceding end of each of the first and second recording units, with regard to the recording unit sequence produced by using the second recording format.

8. The digital audio recording apparatus according to claim 1, wherein said formatting means further inserts the recording format data for discerning the first recording format and the second recording format into said recording unit sequence.

9. A digital audio reproduction apparatus comprising: an input end for receiving data formatted by using one of a first recording format and a second recording format, wherein the first recording format is for forming a first recording unit containing transformation coefficients belonging to each reference unit, and the second recording format is for forming a second recording unit containing transformation coefficients in a lower frequency area and a third recording unit containing transformation coefficients in a higher frequency area among transformation coefficients contained in each reference unit; a digital-to-analog (D/A) converter for digital-to-analog converting an input digital audio signal according to a predetermined operating frequency; means, coupled to said input end, for discriminating sampling frequency of the audio signal contained in the input formatted data and, a recording format, and outputting data representing the discrimination result; inverse formatting means, coupled to said input end and receiving data output from means for discriminating, for inversely formatting the formatted data received according to comparison between the discriminated sampling frequency and the predetermined operating frequency, and the discriminated recording format of the prestored first and second recording formats; and inverse transformation means having an inverse transformation characteristic optimized to said D/A converter, for transforming the transformation coefficients output from said inverse formatting means into audio samples in a temporal domain, and supplying resultant audio samples to said D/A converter.

10. The digital audio reproduction apparatus according to claim 9, wherein said input end receives said formatted data from the digital recording medium.

11. The digital audio reproduction apparatus according to claim 9 or 10, wherein said each recording unit is determined based on a data amount which can be continuously recorded on said digital recording medium according to a signal recording characteristic of the digital recording medium.

12. The digital audio reproduction apparatus according to claim 9, 10 or 11, wherein said lower frequency area and said higher frequency area are bisected from the whole frequency area represented by transformation coefficients.

13. The digital audio reproduction apparatus according to claim 9, 10, 11 or 12, wherein said inverse formatting means supplies to said inverse transformation means the transformation coefficients of the lower frequency area among transformation coefficients contained in the first recording unit, in the case that the discriminated sampling frequency is said predetermined operating frequency multiplies by factors of two, and the discriminated recording format is the first recording format.

14. The digital audio reproduction apparatus according to claim 9, 10, 11, 12 or 13, wherein said inverse formatting means supplies the transformation coefficients contained in the second recording unit to said inverse transformation means, in the case that the discriminated sampling frequency is said predetermined operating frequency multiplied by factors of two, and the discriminated recording format is the second recording format.

15. The digital audio reproduction apparatus according to claim 9, wherein said inverse formatting means supplies all transformation coefficients to said inverse transformation means when said predetermined operating frequency is the discriminated sampling frequency multiplied by factors of two, and said inverse transformation means performs zero padding for every reference unit prior to inversely transforming the transformation coefficients received from said inverse transformation means.

16. A digital audio recording apparatus substantially as herein described with reference to Figure 1 to 3.

17. A digital audio reproduction apparatus substantially as herein described with reference Figures 3 and 4.

18. A digital audio reproduction apparatus as herein described with reference to Figures 3 and 5.