CLAIMS

1.

A portable information terminal comprising: a memory (142) for storing data; expansion processing means (202) stored in said memory (142), for expanding compressed data which has not been sub jected to variablelength coding, into audio data; sound output means (156,184) for converting the audio data into sound and outputting the sound; and a plurality of data buffers (BUF1, BUF2, BUF11, BUF12) accessible by at least said expansion processing means (202), for successively selectively reading and writing at least said audio data.

2.

A portable information terminal according to claim 1, wherein the number of data based on a processable number that is preset to meet the performance of at least said sound output means (156,184) is regarded as one sample, and said expansion processing means (202) comprises means for expanding the compressed data for each sample.

3.

A portable information terminal according to claim 1 or 2, wherein said expansion processing means (202) com prises: inverse quantization processing means (246) for in versely quantizing said compressed data into inversely quan tized data; and IDCT processing means (248) for effecting an IDCT proc ess on said inversely quantized data to produce said audio data; said plurality of data buffers (BUF1, BUF2, BUF11, BUF12) including: two inverse quantization buffers (BUF1, BUF2) accessi ble for successively selectively reading and writing said inversely quantized data; and two audio data buffers (BUF11, BUF12) accessible for successively selectively reading and writing said audio data.

4.	A portable information terminal according to any one of claims 1 to 3, wherein said IDCT processing means (248) comprises means for effecting the IDCT process using a cosi ne table which has been generated in advance.

5.	A portable information terminal according to any one of claims 1 to 4, wherein said IDCT processing means (248) has lowpass filter processing means (250) for logically ef fecting a lowpass filter on IDCTprocessed data to reduce a highfrequency component contained therein.

6.	A portable information terminal according to any one of claims 1 to 5, further comprising: communication means (160 or 170) for sending data to and receiving data from an external device; said compressed data comprising data stored in said memory (142) via said communication means (160 or 170).

7.	A portable information terminal according to claim 6, wherein said compressed data comprises data which is pro duced when uncompressed data recorded in a recording medium (40) accessible via said external device is compressed by said external device.

8.	A portable information terminal according to claim 6, wherein said compressed data comprises data which is re corded in a recording medium (40) accessible via said exter nal device and compressed when recorded in said recording medium (40).

9.	A portable information terminal according to claim 7 or 8, wherein said uncompressed data is compressed by ef fecting a DCT process on the uncompressed data to produce DCTprocessed data and quantizing the DCTprocessed data.

10.

A portable information terminal according to claim 9, wherein said DCTprocessed data is quantized by determin ing maximum values at respective frequencies of the DCT processed data to generate a quantization table containing the maximum values at the respective frequencies, and divid ing the DCTprocessed data by the maximum values at the re spective frequencies in the quantization table to produce quantized data.

11.	A portable information terminal according to any one of claims 6 to 10, wherein said compressed data compris es data containing reduced noise.

12.

A portable information terminal according to claim 11, wherein the noise is reduced by calculating a total of samples in original data to produce an original total value, compressing the original data and expanding the compressed original data to produce restored data, calculating a total of samples in the restored data to produce a restored total value, comparing said original total value and said restored total value with each other, and correcting said original data depending on the result of comparison.

13.

A method of processing audio data, comprising the steps of: expanding compressed data which has not been subjected to variablelength coding, into audio data, using a plural ity of data buffers (BUF1, BUF2, BUF11, BUF12) accessible for successively selectively reading and writing at least said audio data; and outputting the audio data to sound output means (156, 184) to output sound.

14.

A method according to claim 13, wherein the number of data based on a processable number that is preset to meet the performance of at least said sound output means (156, 184) is regarded as one sample, and said step of expanding compressed data comprises the step of expanding the com pressed data for each sample.

15.

A method according to claim 13 or 14, wherein said step of expanding compressed data comprises the steps of: inversely quantizing said compressed data into inverse ly quantized data; and effecting an IDCT process on said inversely quantized data to produce said audio data; the arrangement being such that said inversely quan tized data is successively selectively read and written us ing two inverse quantization buffers (BUF1, BUF2), and said audio data is successively selectively read and written us ing two audio data buffers (BUF11, BUF12).

16.	A method according to claim 15, wherein said step of effecting an IDCT process comprises the step of effecting the IDCT process using a cosine table which has been gener ated in advance.

17.	A method according to claim 15 or 16, wherein said step of effecting an IDCT process comprises the step of logically effecting a lowpass filter on IDCTprocessed data to reduce a highfrequency component contained therein.

18.	A method according to any one of claims 15 to 17, further comprising the step of generating said compressed data, said step of generating said compressed data compris ing the steps of: effecting a DCT process on uncompressed data to produce DCTprocessed data; and quantizing the DCTprocessed data.

19.

A method according to claim 18, wherein said step of quantizing the DCTprocessed data comprises the steps of: determining maximum values at respective frequencies of the DCTprocessed data to generate a quantization table con taining the maximum values at the respective frequencies; and dividing the DCTprocessed data by the maximum values at the respective frequencies in the quantization table to produce quantized data.

20.	A method according to any one of claims 13 to 19, wherein said compressed data comprises data containing re duced noise.

21.

A method according to claim 20, further comprising the step of reducing noise, said step of reducing noise com prising the steps of: calculating a total of samples in original data to pro duce an original total value; compressing the original data and expanding the com pressed original data to produce restored data; calculating a total of samples in the restored data to produce a restored total value; comparing said original total value and said restored total value with each other, and correcting said original data depending on the result of comparison.

22.

A recording medium (40) which stores a program op erable on a portable information terminal having a memory (142) for storing data, sound output means (156,184) for converting the audio data into sound and outputting the sound, a plurality of data buffers (BUF1, BUF2, BUF11, BUF12) accessible for successively selectively reading and writing at least said audio data, and also stores data referred to by said program, said program comprising the step of: expanding compressed data which has not been subjected to variablelength coding, stored in said memory (142), us ing said data buffers (BUF1, BUF2, BUF11, BUF12), thereby to produce audio data.

23.

A recording medium according to claim 22, wherein the number of data based on a processable number that is preset to meet the performance of at least said sound output means (156,184) is regarded as one sample, and said step of expanding compressed data comprises the step of expanding the compressed data for each sample.

24.

A recording medium according to claim 22 or 23, wherein said portable information terminal (18) has two in verse quantization buffers (BUF1, BUF2) accessible for suc cessively selectively reading and writing said inversely quantized data, and two audio data buffers (BUF11, BUF12) accessible for successively selectively reading and writing said audio data, said step of expanding compressed data com prises the steps of: inversely quantizing said compressed data into inverse ly quantized data; and effecting an IDCT process on said inversely quantized data to produce said audio data.

25.	A recording medium according to any one of claims 22 to 24, wherein said step of effecting an IDCT process comprises the step of effecting the IDCT process using a co sine table which has been generated in advance.

26.	A recording medium according to any one of claims 22 to 25, wherein said step of effecting an IDCT process comprises the step of logically effecting a lowpass filter on IDCTprocessed data to reduce a highfrequency component contained therein.

27.	A recording medium according to any one of claims 22 to 26, which stores said compressed data as well as said program.

28.	A recording medium according to any one of claims 22 to 27, which said program comprises the step of: compressing uncompressed data; said uncompressed data as well as said program being stored in said recording medium.

29.	A recording medium according to claim 28, wherein said step of compressing uncompressed data comprises the stepsof: effecting a DCT process on the uncompressed data to produce DCTprocessed data; and quantizing the DCTprocessed data.

30.

A recording medium according to claim 29, wherein said step of quantizing the DCTprocessed data comprises the stepsof: determining maximum values at respective frequencies of the DCTprocessed data to generate a quantization table con taining the maximum values at the respective frequencies; and dividing the DCTprocessed data by the maximum values at the respective frequencies in the quantization table to produce quantized data.

31.	A recording medium according to any one of claims 22 to 30, wherein said compressed data comprises data con taining reduced noise.

32.

A recording medium according to claim 31, further comprising the step of reducing noise, said step of reducing noise comprising the steps of: calculating a total of samples in original data to pro duce an original total value; compressing the original data and expanding the com pressed original data to produce restored data; calculating a total of samples in the restored data to produce a restored total value; comparing said original total value and said restored total value with each other, and correcting said original data depending on the result of comparison.

33.

A program operable on a portable information termi nal having a memory (142) for storing data, sound output means (156,184) for converting the audio data into sound and outputting the sound, a plurality of data buffers (BUF1, BUF2, BUF11, BUF12) accessible for successively selectively reading and writing at least said audio data, and also stores data referred to by said program, said program being readable and executable by a computer, said program compris ing the step of: expanding compressed data which has not been subjected to variablelength coding, stored in said memory (142), us ing said data buffers (BUF1, BUF2, BUF11, BUF12), thereby to produce audio data.