JP4567412B2 - Audio playback device and audio playback method - Google Patents

Description

  The present invention relates to an audio reproducing device and an audio reproducing method, and more particularly to an audio reproducing device and an audio reproducing method suitable for reproducing compressed audio.

  Conventionally, in an audio player, a compressed audio, which is a digital audio signal, is obtained by compressing and encoding an analog audio signal by using a so-called compression algorithm such as MP3 or WMA.

  The compressed audio obtained by compression / encoding is expanded and decoded under a desired reproduction sampling frequency and reproduced.

  Here, FIG. 8 shows a digital encoding format of a general uncompressed sound (original music), and FIG. 9 shows a spectrum of the uncompressed sound, and these are shown in FIGS. Thus, it is known that the upper limit of the recordable frequency of the digitized audio data is about ½ of the sampling frequency of the own signal.

  For example, in the case of a CD, the sampling frequency at the time of encoding is 44.1 kHz, whereas the upper limit of the frequency of music that can be actually recorded on a CD is 22.05 kHz.

JP 2003-333698 A

  However, for compressed audio such as MP3, particularly when encoded at a low bit rate, the sampling frequency at the time of encoding is the same as in FIG. As described above, the upper limit of the frequency band may be cut.

  As a result, even when the compressed audio is reproduced under a reproduction sampling frequency of 44.1 kHz, for example, only the frequency band of about sampling frequency 22.05 kHz or 32 kHz is actually included.

  In other words, conventionally, as a result of loss of a high-frequency signal due to encoding by MP3 or the like, there has been a problem that it is impossible to reproduce sound close to the original sound.

  Therefore, the present invention has been made in view of such a problem, and provides an audio playback device and an audio playback method capable of restoring a sound range lost by compression and reproducing sound close to the original sound. It is intended to do.

In order to achieve the above-mentioned object, the audio player according to the present invention is characterized in that compressed audio that has been compressed and encoded according to a predetermined compression format is expanded and decoded under a desired reproduction sampling frequency and reproduced. In the audio player, a determination device that determines whether or not an upper limit frequency of the frequency band of the compressed sound is less than a predetermined determination frequency suitable for reproduction under the reproduction sampling frequency, and a determination result of the determination device based on a down-sampling processing apparatus for performing the down-sampling process after the low-pass filtering, the down-sampling processing by the down-sampling processing unit is subjected to compressed audio that is an upper limit frequency of the frequency band less than the determination frequency Interpolation processing for interpolating the frequency band lost during the compression is applied to the compressed audio. It lies in having an up-sampling processing apparatus for performing the Nau upsampling process.

According to such a configuration, after the downsampling processing is performed after the low-pass filter processing by the downsampling processing device on the compressed audio whose upper limit frequency of the frequency band is less than the determination frequency, the upsampling processing is further performed. By performing upsampling processing with interpolation processing by the device, it is possible to obtain compressed audio in which the frequency band lost during compression is interpolated, and decompressing and decoding this compressed audio under the reproduction sampling frequency It can be played back.

  In addition, the audio player according to the present invention is characterized in that the determination frequency is a half of the reproduction sampling frequency.

According to such a configuration, after the downsampling processing is performed after the low-pass filter processing by the downsampling processing device for the compressed audio whose upper limit frequency of the frequency band is less than 1/2 of the reproduction sampling frequency, Furthermore, by performing an upsampling process accompanied by an interpolation process by an upsampling processing device, it is possible to obtain a compressed sound in which the frequency band lost during the compression is interpolated. It is possible to reproduce by decompressing and decoding.

Further, the sound reproducing apparatus according to the present invention is characterized in that the determination device is formed so as to determine whether or not the bit rate of the compressed sound satisfies a predetermined condition, and the downsampling treatment device has an upper limit of the frequency band. It is configured to perform a downsampling process after a low-pass filter process on a compressed sound whose frequency is less than the determination frequency and the bit rate satisfies the predetermined condition. is there.

According to such a configuration, the upsampling with the downsampling process after the low-pass filter process and the subsequent interpolation process is performed according to the upper limit frequency of the frequency band of the compressed sound and the bit rate of the compressed sound. It is possible to select whether or not to perform processing.

  Still further, the sound reproducing apparatus according to the present invention is characterized in that the determination device allows the bit rate data satisfying a predetermined condition that differs depending on the reproduction sampling frequency to be mutually shared with the reproduction sampling frequency data corresponding to the bit rate. A table stored in a state of correspondence is provided, and the table is configured to determine whether or not the compressed audio satisfies the predetermined condition with reference to the table.

  According to such a configuration, the determination device can easily and quickly determine whether or not the bit rate satisfies a predetermined condition by referring to the table.

  Further, the audio player according to the present invention is characterized in that the upsampling processing apparatus performs fractal interpolation processing as interpolation processing.

  And according to such a structure, it becomes possible to interpolate the frequency band lost in the compression more appropriately by performing the fractal interpolation process.

Further, the audio reproduction method according to the present invention is characterized in that in the audio reproduction method for reproducing the compressed audio compressed and encoded according to a predetermined compression format under a desired reproduction sampling frequency, the audio is reproduced. When the upper limit frequency of the frequency band of the compressed audio is less than a predetermined determination frequency suitable for reproduction under the reproduction sampling frequency, the compressed audio is subjected to down-sampling processing after low-pass filter processing , Next, the compressed audio subjected to the downsampling process is subjected to an upsampling process with an interpolation process for interpolating a frequency band lost during the compression, and the upsampling with the downsampling process and the interpolation process is performed. The processed compressed audio is decompressed and decompressed under the playback sampling frequency. It turned into and lies in the fact that to play.

According to such a method, by performing the upsampling process with the downsampling process and the interpolation process after the low-pass filter process for the compressed sound whose upper limit frequency of the frequency band is less than the determination frequency, Therefore, it is possible to obtain a compressed sound obtained by interpolating the lost frequency band, and to decompress and decode the compressed sound at a reproduction sampling frequency.

  Furthermore, the sound reproduction method according to the present invention is characterized in that the determination frequency is set to a half of the reproduction sampling frequency.

According to such a method, the upsampling process with the downsampling process and the interpolation process after the low-pass filter process is performed on the compressed sound whose upper limit frequency of the frequency band is less than 1/2 of the reproduction sampling frequency. Thus, it is possible to obtain compressed audio in which the frequency band lost during compression is interpolated, and it is possible to reproduce the compressed audio by decompressing and decoding it under the reproduction sampling frequency.

Further, the audio reproduction method according to the present invention is characterized in that it is determined whether or not the bit rate of the compressed audio satisfies a predetermined condition, and the compressed audio whose upper limit frequency of the frequency band does not satisfy the determination frequency, The downsampling process after the low-pass filter process is performed on the compressed sound whose bit rate satisfies the predetermined condition.

According to such a method, according to the upper limit frequency of the frequency band of the compressed audio and the bit rate of the compressed audio, the upsampling with the downsampling process after the low-pass filter process and the subsequent interpolation process is performed. It is possible to select whether or not to perform processing.

  Furthermore, the audio reproduction method according to the present invention is characterized in that data of a bit rate satisfying the predetermined condition that differs depending on the reproduction sampling frequency is correlated with the data of the reproduction sampling frequency corresponding to the bit rate. A table stored in a laid state is prepared, and it is determined with reference to the table whether or not the compressed sound satisfies the predetermined condition.

  According to such a method, it is possible to easily and quickly determine whether or not the bit rate satisfies a predetermined condition by referring to the table.

  Furthermore, the sound reproduction method according to the present invention is characterized in that fractal interpolation processing is performed as interpolation processing.

  And according to such a method, it becomes possible to interpolate the frequency band lost at the time of compression more appropriately by performing fractal interpolation processing.

According to the sound reproducing device of the present invention, after the downsampling processing is performed after the low-pass filter processing by the downsampling processing device on the compressed sound whose upper limit frequency of the frequency band is less than the determination frequency, the upsampling is further performed. By performing upsampling processing with interpolation processing by the processing device, it is possible to obtain compressed audio in which the frequency band lost during compression is interpolated, and decompressing and decoding this compressed audio under the reproduction sampling frequency As a result, the sound range lost by the compression can be restored, and the sound close to the original sound can be reproduced.

In addition, according to the sound reproducing device of the present invention, the downsampling processing is performed after the low-pass filter processing by the downsampling processing device for the compressed sound whose upper limit frequency of the frequency band is less than 1/2 of the reproduction sampling frequency. After that, by performing an upsampling process accompanied by an interpolation process by the upsampling processing device, a compressed sound in which the frequency band lost during the compression is interpolated can be obtained. As a result, the range lost by compression can be restored, and the sound close to the original sound can be reproduced.

Furthermore, according to the audio player according to the present invention, the downsampling process after the low-pass filter process and the subsequent interpolation process are performed according to the upper limit frequency of the frequency band of the compressed audio and the bit rate of the compressed audio. As a result of being able to select whether or not to perform the upsampling process, the sound range lost by the compression can be restored more satisfactorily, and the sound closer to the original sound can be reproduced.

  Furthermore, according to the sound reproducing device of the present invention, the determination device can easily and quickly determine whether or not the bit rate satisfies the predetermined condition by referring to the table. The lost sound range can be restored more inexpensively and efficiently.

  Further, according to the sound reproducing device of the present invention, by performing the fractal interpolation process, the frequency band lost during the compression can be more appropriately interpolated, and as a result, the sound range lost by the compression can be further increased. The sound can be restored to accuracy, and the sound closer to the original sound can be reproduced.

Furthermore, according to the sound reproduction method according to the present invention, by performing the upsampling process with the downsampling process and the interpolation process after the low-pass filter process for the compressed sound whose upper limit frequency of the frequency band is less than the determination frequency, It is possible to obtain compressed audio in which the frequency band lost during compression is interpolated, and this compressed audio can be decompressed and decoded under the reproduction sampling frequency. The sound can be restored and the sound close to the original sound can be reproduced.

Furthermore, according to the audio reproduction method of the present invention, the upsampling with the downsampling process and the interpolation process after the low-pass filter process for the compressed audio whose upper limit frequency of the frequency band is less than 1/2 of the reproduction sampling frequency. By applying the processing, it is possible to obtain compressed audio in which the frequency band lost during compression is interpolated, and this compressed audio can be decompressed and decoded under the reproduction sampling frequency, resulting in compression. Can restore the lost sound range and reproduce the sound close to the original sound.

Further, according to the audio reproduction method of the present invention, the downsampling process after the low-pass filter process and the subsequent interpolation process are performed according to the upper limit frequency of the frequency band of the compressed audio and the bit rate of the compressed audio. As a result of being able to select whether or not to perform the upsampling process, the sound range lost by the compression can be restored more satisfactorily, and the sound closer to the original sound can be reproduced.

  Furthermore, according to the audio reproduction method of the present invention, it is possible to easily and quickly determine whether or not the bit rate satisfies a predetermined condition by referring to the table. Further, it can be restored at low cost and efficiently.

  Furthermore, according to the audio reproduction method of the present invention, the frequency band lost during the compression can be more appropriately interpolated by performing the fractal interpolation process. It can be restored with high accuracy, and sound closer to the original sound can be reproduced.

  Hereinafter, embodiments of an audio playback device according to the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the audio player 1 in this embodiment has a compressed audio determination unit 2 as a determination device, and the compressed audio determination unit 2 includes music, etc. through CD, broadcast, communication, and the like. Compressed audio is input.

  Based on the compression format of the input compressed audio, the compressed audio determination unit 2 has a reproduction sampling frequency as a determination frequency suitable for reproduction with the upper limit frequency of the frequency band of the compressed audio being reproduced under a predetermined reproduction sampling frequency. It is determined whether or not the frequency is less than half the frequency.

  Further, the compressed audio determination unit 2 determines whether or not the value of the bit rate satisfies a predetermined condition that differs depending on the reproduction sampling frequency, based on the bit rate (bps) of the input compressed audio. It is like that.

  For the predetermined condition, a suitable value may be selected in relation to the reproduction sampling wave number. For example, when the reproduction sampling frequency is 44.1 kHz, the predetermined condition may be 96 kbps or less.

  Further, a table as shown in Table 1 below is prepared in the compressed sound determination unit 2, and data of a plurality of bit rates satisfying the predetermined condition that differs depending on the reproduction sampling frequency are included in this table. The reproduction sampling frequency data corresponding to each bit rate may be stored in correspondence with each other.

例えば、表１においては、再生サンプリング周波数が４４．１ｋＨｚの場合における所定の条件を満足するビットレートは、表１の左欄に示すように、３２ｋｂｐｓ、６４ｋｂｐｓおよび９６ｋｂｐｓとなっている。圧縮音声がこれらのビットレートの値をとる場合には、表１の右欄に示すように、圧縮音声に対して後述するＦＩＦアップサンプリング処理（表１右欄におけるＦＩＦ処理）が施されるようになっている。なお、この場合、デジタル的には、表１の右欄に示すように、ＦＩＦ処理を制御するための信号の値が１となる。一方、表１において、１２８ｋｂｐｓ、１６０ｋｂｐｓ等のビットレートは、再生サンプリング周波数が４４．１ｋＨｚの下での所定の条件を満足しないものとなり、この場合には、前記信号の値は０となり、ＦＩＦアップサンプリング処理は施されないことになる。

For example, in Table 1, as shown in the left column of Table 1, the bit rates that satisfy the predetermined condition when the reproduction sampling frequency is 44.1 kHz are 32 kbps, 64 kbps, and 96 kbps. When the compressed audio takes these bit rate values, as shown in the right column of Table 1, the IF upsampling processing (FIF processing in the right column of Table 1) described later is performed on the compressed audio. It has become. In this case, digitally, as shown in the right column of Table 1, the value of the signal for controlling the IF processing is 1. On the other hand, in Table 1, bit rates such as 128 kbps and 160 kbps do not satisfy a predetermined condition when the reproduction sampling frequency is 44.1 kHz. In this case, the value of the signal is 0, and the FIFO is increased. Sampling processing is not performed.

  In Table 1, as shown in the left column of Table 1, the bit rates that satisfy the predetermined condition when the reproduction sampling frequency is 48.0 kHz are 32 kbps, 64 kbps, and 96 kbps. When the compressed audio takes these bit rate values, as shown in the right column of Table 1, the value of the signal becomes 1, and the IF upsampling processing (FIF processing in the right column of Table 1) is applied to the compressed audio. ) Is given. On the other hand, in Table 1, bit rates such as 128 kbps and 160 kbps do not satisfy the predetermined condition when the reproduction sampling frequency is 48.0 kHz. In this case, the value of the signal is 0, and the FIFO is increased. Sampling processing is not performed.

  In this way, it is possible to easily and quickly determine whether or not the bit rate of the input compressed audio satisfies the predetermined condition by referring to the table.

  A downsampling processing unit 3 as a downsampling processing device is connected to the output side of the compressed sound determination unit 2.

  The downsampling processing unit 3 receives from the compressed audio determination unit 2 compressed audio having a format in which the upper limit frequency of the frequency band as shown in FIG. Compressed sound whose rate satisfies the predetermined condition and which requires downsampling processing (hereinafter referred to as “corresponding compressed sound”) is input.

The down-sampling processing unit 3 performs low-pass filter processing and subsequent down-sampling processing (hereinafter simply referred to as “down-sampling processing”) on the input compressed audio, and performs this down-sampling processing. The corresponding compressed audio is output.

  In the downsampling process, for example, as shown in FIG. 3, the sampling frequency Fs ′ after the downsampling process may be half Fs ′ of the reproduction sampling frequency Fs.

  An FIF (Fractal Interpolation Functions) upsampling processing unit 4 as an upsampling processing device is connected to the output side of the downsampling processing unit 3.

  The FIF upsampling processing unit 4 is input with the corresponding compressed audio output from the downsampling processing unit 3 after downsampling processing.

  Then, the FIFO upsampling processing unit 4 performs upsampling processing (hereinafter referred to as “FIF upsampling processing”) with the fractal interpolation processing as shown in FIGS. 4 and 5 on the input compressed speech after the downsampling processing. The frequency band lost at the time of compression is interpolated.

  In the fractal interpolation processing, the compressed speech is regarded as a figure having a waveform as shown in FIG. 5, for example, and the figure of the compressed voice is reduced, enlarged or rotated as appropriate by a self-similar figure, that is, a single line segment. This is a process of interpolating the frequency band lost by using the line segment, assuming that the figure is configured by connecting the objects together. Such a fractal interpolation process is a very suitable technique for reproducing a sound close to the original sound with high accuracy.

  Therefore, in the present embodiment, after downsampling processing is performed on the compressed audio by the downsampling processing unit 3, and further, the IF upsampling processing unit 4 performs the IF upsampling processing, so that it is lost during compression. The interpolated frequency band can be appropriately interpolated.

  The FIF upsampling processing unit 4 is immediately supplied with compressed audio in a format other than the corresponding compressed audio from the compressed audio determining unit 2. As this compressed sound, for example, while the reproduction sampling frequency is 44.1 kHz, the upper limit frequency of the frequency band is 1 of the reproduction sampling frequency Fs as in the compressed sound compressed at the sampling frequency of 22.05 kHz. Compressed audio that has a format less than / 2 and does not require downsampling processing.

  Then, the IF upsampling processing unit 4 also performs the IF upsampling process on the compressed sound input directly from the compressed sound determination unit 2 and outputs the compressed sound subjected to the IF upsampling process. It has become.

  A post-processing unit 5 made up of an equalizer (EQ), TCR, or the like is connected to the output side of the FIF up-sampling processing unit 4. The compressed audio after the upsampling process is input.

  The post-processing unit 5 performs post-processing (post-processing) for adjusting the sound quality, the sound generation timing, etc., on the input compressed sound, and outputs the result.

  The compressed sound output from the post-processing unit 5 is decompressed and decoded via D / A or the like and output from a speaker (not shown).

  In some cases, the compressed speech is immediately input from the compressed speech determination unit 2 to the post-processing unit 5. As the compressed sound in this case, for example, compression that can be considered that the upper limit frequency of the frequency band of lossless compressed audio or the like whose sound range is hardly cut during compression has reached 1/2 of the reproduction sampling frequency Fs. Applicable to audio.

  Next, an embodiment of a sound reproduction method according to the present invention will be described with reference to FIGS.

  The sound reproducing method in the present embodiment can be executed by using the sound reproducing device 1 described above as one means.

  That is, first, in step 1 (ST1) of FIG. 6, the compressed sound determination unit 2 acquires compressed sound through CD, broadcasting, communication, or the like.

  Next, in step 2 (ST2), the compressed audio determination unit 2 determines whether or not the upper limit frequency of the frequency band of the compressed audio acquired in step 1 (ST1) is less than 1/2 of the reproduction sampling frequency Fs. .

  Further, in step 2 (ST2), the compressed audio determination unit 2 determines whether or not the bit rate of the compressed audio acquired in step 1 (ST1) satisfies a predetermined condition in relation to the reproduction sampling frequency. .

  In step 2 (ST2), when the upper limit frequency of the frequency band of the compressed audio is less than ½ of the reproduction sampling frequency Fs and the bit rate satisfies the predetermined condition, step 3 Proceed to (ST3), otherwise proceed to step 6 (ST6).

  In step 3 (ST3), the compressed audio determination unit 2 causes the compressed audio whose frequency band upper limit frequency is less than 1/2 of the reproduction sampling frequency Fs, and the bit rate satisfies the predetermined condition. It is determined whether or not the compressed sound to be compressed is a compressed sound that requires downsampling processing.

  In step 3 (ST3), if the compressed audio is compressed audio that requires downsampling processing (corresponding compressed audio), the process proceeds to step 4 (ST4), and if the compressed audio is compressed audio that does not require downsampling processing. Advances to step 5 (ST5).

  In step 4 (ST4), the downsampling processing unit 3 applies a downsampling process to the compressed sound, and then the process proceeds to step 5 (ST5).

  Next, in step 5 (ST5), the FIFO upsampling processing unit 4 performs an IF upsampling process on the compressed audio.

  As a result, as shown in FIG. 7, a compressed sound in which the frequency band lost during the compression is appropriately interpolated can be obtained. Note that the frequency band interpolated by the FIF upsampling process includes not only a high sound range but also a sound range corresponding to a minute signal that has been deleted in the vicinity of a large signal. Furthermore, as shown in FIG. 7, it is also possible to generate a high frequency range that is not found in the original music.

  Finally, in step 6 (ST6), the compressed sound is decompressed and decoded and reproduced.

  As described above, according to the present embodiment, it is possible to obtain a compressed sound obtained by interpolating the frequency band lost in the compression by performing the IF upsampling process on the compressed sound. The lost sound range can be restored with high accuracy, and high-quality sound close to the original sound before compression can be reproduced.

  In addition, this invention is not limited to embodiment mentioned above, A various change is possible as needed.

  For example, interpolation processing for interpolating a frequency band lost during compression may be performed by a method other than fractal interpolation processing.

  Further, by applying the above-described FIF upsampling processing to an uncompressed source such as a CD and generating a high sound range that is not included in the original music, it is possible to achieve high sound quality equivalent to that of DVD audio.

1 is a block diagram showing an embodiment of an audio player according to the present invention. Explanatory drawing which shows the digital encoding format of applicable compression audio | voice in embodiment of the audio | voice reproducing device based on this invention. Explanatory drawing which shows the digital encoding format of the corresponding compression audio | voice after downsampling in embodiment of the audio | voice reproducing apparatus based on this invention. Explanatory drawing which shows the digital encoding format of the applicable compression audio | voice which performed the IF upsampling process in embodiment of the audio | voice reproducing device based on this invention The conceptual diagram which shows the fractal interpolation process in embodiment of the audio | voice player based on this invention The flowchart which shows embodiment of the audio | voice reproduction | regeneration method based on this invention The figure which shows the spectrum of the compression audio | voice in which the frequency band lost at the time of compression was interpolated in embodiment of the audio | voice reproduction method which concerns on this invention Explanatory drawing showing a digital encoding format of general uncompressed audio Diagram showing a general uncompressed audio spectrum Explanatory drawing which shows the digital encoding format of the compression audio | voice from which the upper limit of the frequency band was cut Diagram showing the spectrum of compressed audio with the upper limit of the frequency band cut

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Audio | voice player 2 Compressed sound determination part 3 Downsampling process part 4 FIF upsampling process part

Claims (10)

In an audio reproducing apparatus that reproduces compressed audio that has been compressed and encoded according to a predetermined compression format by decompressing and decoding it under a desired reproduction sampling frequency.
A determination device for determining whether an upper limit frequency of the frequency band of the compressed audio is less than a predetermined determination frequency suitable for reproduction under the reproduction sampling frequency;
Based on the determination result of this determination device, a downsampling processing device that performs downsampling processing after low-pass filter processing for compressed speech whose upper limit frequency of the frequency band is less than the determination frequency;
The compressed audio, wherein the down-sampling process is performed by the down-sampling processing unit, and a up-sampling processing unit that performs up-sampling processing with the interpolation process of interpolating a frequency band that may have been lost during the compression An audio player characterized by that.   The sound reproducing apparatus according to claim 1, wherein the determination frequency is a half of the reproduction sampling frequency. The determination device is configured to determine whether or not a bit rate of the compressed audio satisfies a predetermined condition,
The down-sampling treatment apparatus performs the down-sampling process on compressed audio whose upper limit frequency of the frequency band is less than the determination frequency and whose bit rate satisfies the predetermined condition. The sound reproducing device according to claim 1 or 2, wherein the sound reproducing device is formed as follows.   The determination apparatus includes a table storing bit rate data satisfying the predetermined condition that differs according to the reproduction sampling frequency in a state of having a corresponding relationship with the reproduction sampling frequency data corresponding to the bit rate. The audio player according to claim 3, further comprising: determining whether or not the compressed audio satisfies the predetermined condition with reference to the table.   5. The sound reproducing device according to claim 1, wherein the upsampling processing device performs a fractal interpolation process as the interpolation process. 6. In an audio reproduction method for reproducing compressed audio that has been compressed and encoded in accordance with a predetermined compression format, decompressed and decoded under a desired reproduction sampling frequency,
When the upper limit frequency of the frequency band of the compressed audio does not reach a predetermined determination frequency suitable for reproduction under the reproduction sampling frequency, downsampling processing is performed on the compressed audio after low-pass filter processing. ,
Next, the compressed audio subjected to the downsampling process is subjected to an upsampling process with an interpolation process for interpolating a frequency band lost during the compression,
An audio reproduction method characterized in that the compressed audio subjected to the upsampling process accompanied with the downsampling process and the interpolation process is decompressed and decoded under the reproduction sampling frequency.   The audio reproduction method according to claim 6, wherein the determination frequency is a half of the reproduction sampling frequency. Determining whether the bit rate of the compressed audio satisfies a predetermined condition;
7. The downsampling process is performed on compressed audio in which the upper limit frequency of the frequency band is less than the determination frequency and the bit rate satisfies the predetermined condition. Or the audio | voice reproduction method of Claim 7.   Preparing a table storing bit rate data satisfying the predetermined condition depending on the reproduction sampling frequency in a state of having a corresponding relationship with the reproduction sampling frequency data corresponding to the bit rate; 9. The audio reproduction method according to claim 8, wherein whether or not the audio satisfies the predetermined condition is determined with reference to the table.   10. The audio reproduction method according to claim 6, wherein fractal interpolation processing is performed as the interpolation processing.

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