Methods of efficiently recording an audio signal in semiconductor memory

• US 5,630,010 A
• Filed: 09/29/1995
• Issued: 05/13/1997
• Est. Priority Date: 04/20/1992
• Status: Expired due to Term

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Sugiyama, Kazuhiro, Ono, Yukari
• Primary Examiner(s): Hafiz, Tariq R.
• Application Number:
  US08/536,356
• Time in Patent Office: 592 Days
• Field of Search: 381/42-44, 381/51, 381/29, 395/2, 395/2.1, 395/2.35, 395/2.67, 395/2.71, 395/2.81, 395/2.76, 395/2.28, 395/2.38, 395/2.32
• US Class Current: 704/201
• CPC Class Codes: G11C 2207/16 Solid state audio deprecated, only for historical reasons, G06F3/16, G11B
• CPC Class Codes: G11C 7/16 Storage of analogue signals in digital stores using an arrangement comprising analogue/digital [A/D] converters, digital memories and digital/analogue [D/A] converters

Abstract

An audio signal is recorded in a semiconductor memory in a plurality of hierarchical levels, with the lowest level being adequate for reproduction with a certain reduced degree of fidelity. Successively higher hierarchical lends provide successively greater fidelity when produced. When the memory has been determined to have reached maximum capacity, recording continues by overwriting the highest hierarchical level of data currently stored in the memory with lower hierarchical levels of new data. A code is recorded in the memory, indicating the number of hierarchical levels recorded therein, for subsequent reproduction. The audio signal can furthermore be recorded in variable-length frames and reproduced at high speed by reading every N-th frame, N being a positive integer, or by reading only frames having at least a certain minimum length.

Claims

1. A method of high speed decoding of an audio signal hierarchically encoded by,

(a) digitizing the audio signal, and

(b) hierarchically encoding the digitized audio signal into a plurality of frames, step (b) including, for encodation of each of the plurality of frames, the substeps of,

(1) encoding a relatively lowest hierarchical level with a first number of bits, from a first portion of the digitized audio signal below a first predetermined frequency, and

(2) encoding a relatively higher hierarchical level with a second number of bits, greater than the first number of bits, from a portion of the digitized audio signal below a second predetermined frequency greater than the first predetermined frequency, the encoded relatively higher hierarchical level further excluding the encoded first portion of the digitized audio signal, the method of decoding comprising the steps of:

(a) determining a predetermined minimal frame length; and

(b) decoding only each of the plurality of frames greater than the predetermined minimal frame length, step (b) including, for decoding each of the plurality of frames, the substeps of,

(1) identifying the first number of bits of the relatively lowest hierarchical level and the second number of bits of the relatively higher hierarchical level,

(2) decoding the encoded relatively lowest hierarchical level based upon the identified first number of bits,

(3) decoding the encoded relatively higher hierarchical level based upon the identified second number of bits, and

(4) converting the decoded relatively lowest and higher hierarchical levels of substeps (2) and (3) into an audio signal.

2. The method of claim 1, wherein step (b) of hierarchically encoding the digitized audio signal further includes the substep of,

(3) encoding n hierarchical levels, each with a number of bits greater than a number of bits of an immediately preceding hierarchical level, each of the n hierarchical levels being encoded from a portion of the digitized audio signal below a predetermined frequency greater than a predetermined frequency of an immediately preceding hierarchical level, and excluding a portion of the digitized audio signal encoded by all preceding hierarchical levels, wherein n is an integer, and wherein step (a) of the decoding method includes identifying the number of bits of each of the n hierarchical levels, step (c) of the decoding method includes decoding each of the n hierarchical levels based on the corresponding identified number of bits and step (d) of the decoding method includes converting each of the decoded n hierarchical levels of step (c) into an audio signal.

3. The method of claim 2, wherein substeps (b1), (b2) and (b3) of hierarchically encoding the digitized audio signal exclude an inaudible portion of the digitized audio signal from being encoded and decoded.

4. The method of claim 3, wherein substeps (b2) and (b3) of hierarchically encoding the digitized audio signal further exclude a portion of the digitized audio signal, masked by a previously encoded portion, from being encoded and decoded.

5. The method of claim 1, where step (a) of hierarchically encoding the digitized audio signal includes the substeps of:

(1) dividing the audio signal into segments of a predetermined length; and

(2) generating frequency coefficients corresponding to each segment.

6. The method of claim 5, wherein hierarchically encoding the digitized audio signal further includes the step of:

(c) determining, prior to step (b), the first and second number of bits based upon the generated frequency coefficients.

7. The method of claim 3, wherein step (b) of hierarchically encoding the digitized audio signal further includes the substep of,

(3) encoding n hierarchical levels, each with a number of bits greater than a number of bits of an immediately preceding hierarchical level, each of the n hierarchical levels being encoded from a portion of the digitized audio signal below a predetermined frequency greater than a predetermined frequency of an immediately preceding hierarchical level, and excluding a portion of the digitized audio signal encoded by all preceding hierarchical levels, wherein n is an integer and wherein the number of bits for encoding each of the n hierarchical levels is determined in step (c), based upon the generated frequency coefficients, and wherein step (a) of the decoding method includes identifying the number of bits of each of the n hierarchical levels, step (c) of the decoding method includes decoding each of the n hierarchical levels based on the corresponding identified number of bits and step (d) of the decoding method includes converting each of the decoded n hierarchical levels of step (c) into an audio signal.

8. The method of claim 1, wherein only an audible portion of the digitized audio signal is hierarchically encoded and decoded.

9. The method of claim 1, wherein substeps (b1) and (b2) of hierarchically encoding the digitized audio signal exclude an inaudible portion of the digitized audio signal from being encoded and decoded.

10. The method of claim 9, wherein substep (b2) of hierarchically encoding the digitized audio signal further excludes a portion of the digitized audio signal, masked by the first portion, from being encoded and decoded.

11. A method of decoding an audio signal, hierarchically encoded by,

(a) digitizing the audio signal, and

(b) hierarchically encoding the digitized audio signal, step (b) including the substeps of,

(1) encoding a relatively lowest hierarchical level with a first number of bits, from a first portion of the digitized audio signal below a first predetermined frequency, and

(2) encoding a relatively higher hierarchical level with a second number of bits, greater than the first number of bits, from a portion of the digitized audio signal below a second predetermined frequency greater than the first predetermined frequency, the encoded relatively higher hierarchical level further excluding the encoded first portion of the digitized audio signal, the method of decoding comprising the steps of:

(a) identifying the first number of bits of the relatively lowest hierarchical level and the second number of bits of the relatively higher hierarchical level;

(b) decoding the encoded relatively lowest hierarchical level based upon the identified first number of bits;

(c) decoding the encoded relatively higher hierarchical level based upon the identified second number of bits; and

(d) converting the decoded relatively lowest and higher hierarchical levels of steps (b) and (c) into an audio signal.

12. The method of claim 11, wherein step (b) of hierarchically encoding the digitized audio signal further includes the substep of,

(3) encoding n hierarchical levels, each with a number of bits greater than a number of bits of an immediately preceding hierarchical level, each of the n hierarchical levels being encoded from a portion of the digitized audio signal below a predetermined frequency greater than a predetermined frequency of an immediately preceding hierarchical level, and excluding a portion of the digitized audio signal encoded by all preceding hierarchical levels, wherein n is an integer, and wherein step (a) of the decoding method includes identifying the number of bits of each of the n hierarchical levels, step (c) of the decoding method includes decoding each of the n hierarchical levels based on the corresponding identified number of bits and step (d) of the decoding method includes converting each of the decoded n hierarchical levels of step (c) into an audio signal.

13. The method of claim 12, wherein substeps (b1), (b2) and (b3) of hierarchically encoding the digitized audio signal exclude an inaudible portion of the digitized audio signal from being encoded and decoded.

14. The method of claim 13, wherein substeps (b2) and (b3) of hierarchically encoding the digitized audio signal further exclude a portion of the digitized audio signal, masked by a previously encoded portion, from being encoded and decoded.

15. The method of claim 11, where step (a) of hierarchically encoding the digitized audio signal includes the substeps of:

(1) dividing the audio signal into segments of predetermined length; and

(2) generating frequency coefficients corresponding to each segment.

16. The method of claim 15, wherein hierarchically encoding the digitized audio signal further includes the step of:

(c) determining, prior to step (b), the first and second number of bits based upon the generated frequency coefficients.

17. The method of claim 16, wherein step (b) of hierarchically encoding the digitized audio signal further includes the substep of,

(3) encoding n hierarchical levels, each with a number of bits greater than a number of bits of an immediately preceding hierarchical level, each of the n hierarchical levels being encoded from a portion of the digitized audio signal below a predetermined frequency greater than a predetermined frequency of an immediately preceding hierarchical level, and excluding a portion of the digitized audio signal encoded by all preceding hierarchical levels, wherein n is an integer and wherein the number of bits for encoding each of the n hierarchical levels is determined in step (c), based upon the generated frequency coefficients, and wherein step (a) of the decoding method includes identifying the number of bits of each of the n hierarchical levels, step (c) of the decoding method includes decoding each of the n hierarchical levels based on the corresponding identified number of bits and step (d) of the decoding method includes converting each of the decoded n hierarchical levels of step (c) into an audio signal.

18. The method of claim 11, wherein only an audible portion of the digitized audio signal is hierarchically encoded and decoded.

19. The method of claim 11, wherein substeps (b1) and (b2) of hierarchically encoding the digitized audio signal exclude an inaudible portion of the digitized audio signal from being encoded and decoded.

20. The method of claim 19, wherein substep (b2) of hierarchically encoding the digitized audio signal further excludes a portion of the digitized audio signal, masked by the first portion, from being encoded and decoded.

21. A decoder for decoding an audio signal, hierarchically encoded by an encoder including,

a first device for digitizing an audio signal into frequency coefficients,

a bit allocator for determining a number of bits to be allocated for encodation in each of a plurality of hierarchical levels based upon the frequency coefficients;

and

a hierarchical quantizer for encoding a relatively lowest hierarchical level of a first number of bits, based upon the determined allocation, from a first portion of the digitized audio signal below a first predetermined frequency, and for encoding a relatively higher hierarchical level with a second number of bits, based upon the determined allocation and greater than the first number of bits, from a portion of the digitized audio signal below a second predetermined frequency greater than the first predetermined frequency, the encoded relatively higher hierarchical level further excluding the encoded first portion of the digitized audio signal, the hierarchical decoder comprising;

first means for identifying the first number of bits of the relatively lowest hierarchical level and the second number of bits of the relatively higher hierarchical level;

second means for decoding the encoded relatively lowest hierarchical level based upon the identified first number of bits and for decoding the encoded relatively higher hierarchical level based upon the identified second number of bits; and

third means for converting the decoded relatively lowest and higher hierarchical levels into an audio signal.