Unary coding scheme for digital audio signals

• US 6,711,546 B1
• Filed: 07/14/2000
• Issued: 03/23/2004
• Est. Priority Date: 07/19/1999
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Thomas, David R.
• Primary Examiner(s): MCFADDEN, SUSAN IRIS
• Application Number:
  US09/616,691
• Time in Patent Office: 1,348 Days
• Field of Search: 704/500, 704/501, 704/502, 704/503, 704/504, 381/338, 381/332
• US Class Current: 704/500
• CPC Class Codes: G11B 20/00007 Time or data compression or expansion audio compression based on psychoacoustics G10L19/00; data processing for reproducing audio data at different playback speeds G10L21/04; video compression H04N19/00; data compression per se H03M7/30
• CPC Class Codes: G11B 20/10527 Audio or video recording; Data buffering arrangements G11B20/12 - G11B20/18 take precedence
• CPC Class Codes: H03M 7/00 Conversion of a code where information is represented by a given sequence or number of digits to a code where the same , similar or subset of information is represented by a different sequence or number of digits

Abstract

A coding scheme for digital audio signals. A method of coding a unary digital audio signal is provided for compressing a set of unary digital audio signal data comprising a succession of absolute amplitude values associated with respective sample periods of the digital audio signal, the absolute amplitude values being integers of positive or zero value, representing the number of speaker elements of a unary digital loudspeaker that are to be active in a sample period. The data is compressed by calculating the numerical difference between adjacent ones of the absolute amplitude values, thereby to convert the succession of absolute amplitude values into a corresponding succession of difference amplitude values. Each difference amplitude values is expressed as a sign bit and a plurality of data bits, representing the change in the number of speaker elements of a unary digital loudspeaker that are to be active in a given sample period relative to the immediately preceding sample period. A corresponding method of decoding the compressed signal is also provided, together with associated encoding and decoding apparatuses.

Claims

1. A method of coding a digital audio signal, the method comprising:

(a) receiving a set of digital audio signal data comprising a succession of absolute amplitude values associated with respective sample periods of the digital audio signal; and

(b) calculating the numerical difference between adjacent ones of the absolute amplitude values, thereby to convert the succession of absolute amplitude values into a corresponding succession of difference amplitude values, wherein the absolute amplitude values are integers of positive or zero value, representing the number of speaker elements of a unary digital loudspeaker that are to be active in the sample period concerned, and the difference amplitude values are integers of positive, negative or zero value, representing the change in the number of speaker elements of a unary digital loudspeaker that are to be active in the sample period concerned relative to the immediately preceding sample period.

2. A method according to claim 1, wherein the difference amplitude values are represented by a sign bit and a plurality of data bits.

3. A method according to claim 2, further comprising:

(c) dividing each difference amplitude value by a pre-determined volume value, thereby to obtain a succession of reduced difference amplitude values, the pre-determined volume value reflecting a desired average number of speaker elements of a unary digital loudspeaker that are to be active over the sample periods of the set of digital audio signal data.

4. A method according to claim 3, wherein the reduced difference amplitude values are integers of positive, negative or zero value, representing a fraction of the change in the number of speaker elements of a unary digital loudspeaker that are to be active in the sample period concerned relative to the immediately preceding sample period.

5. A method according to claim 4, wherein the set of digital audio signal data is received with the succession of absolute amplitude values in binary form, the absolute amplitude values then being converted from binary to unary form prior to calculating the numerical difference between adjacent ones of the absolute amplitude values.

6. A method according to claim 4, wherein the absolute amplitude values, once converted from binary to unary form, are represented by a plurality of data bits, with the absolute amplitude value for each sample corresponding to the number of data bits which are set in each plurality of data bits.

7. A method according to claim 6, wherein the data bits of each sample which are set are grouped into a continuous pulse, the width of which represents the number of speaker elements of a unary digital loudspeaker that are to be active in the sample period concerned.

8. A digital audio product comprising a header containing a product identifier, and at least one audio data block containing a succession of difference amplitude values, each difference amplitude value being an integer of positive, negative or zero value, representing the change in the number of speaker elements of a unary digital loudspeaker that are to be active in one sample period relative to the immediately preceding sample period.

9. A digital audio product according to claim 8, wherein the or each audio data block further contains a pre-determined volume value by which each of the difference amplitude values in the associated data block are to be multiplied in an initial phase of decompression of the difference amplitude values.

11. A transmission medium on which is borne a signal communicating a digital audio product according to claim 9.

12. A transmission medium according to claim 11, wherein the transmission medium is air, an electrical cable or an optical fibre.

10. A data carrier including a recording medium in which is stored a digital audio product according to 9.

13. An encoder for compressing a unary digital audio signal containing a succession of amplitude values, each representing sound amplitude during a sample period, the encoder comprising:

(a) an encoder input for receiving a unary digital audio signal;

(b) a subtractor having a first input connected to receive the unary digital audio signal from the encoder input;

(c) a delay line connected to receive the unary digital audio signal from the encoder input and to relay that signal after a delay of one sample period to a second input of the subtractor; and

(d) an encoder output connected to receive a compressed digital audio signal from the subtractor containing a succession of difference amplitude values, each representing a numerical difference between ones of the amplitude values in the unary digital audio signal received at the encoder input.

14. An encoder according to claim 13, further comprising:

(e) a divider connected between the subtractor and the encoder output and operable to divide each difference amplitude value received from the subtractor by a defined volume value.

15. An encoder according to claim 14, further comprising:

(f) an external input connected to allow external definition of the volume value supplied to the divider.

16. An encoder according to claim 14, further comprising:

(f) a computational unit arranged to receive a succession of amplitude values, each representing sound amplitude during a sample period, and to compute therefrom an average amplitude value, and, in turn, a value for the volume value, the computational unit having an output connected to the divider for supplying to the divider with the volume value thus computed.

17. A transmitter, wireless transmitter or recording device comprising an encoder according to claim 15.

18. A method of decoding a compressed unary digital audio signal to generate a decoded signal, the method comprising:

(a) receiving a succession of difference amplitude values, each representing a difference in sound amplitude between sample periods; and

(b) adding to successive ones of the difference amplitude values an amplitude value derived from preceding ones of the difference amplitude values and a start value, thereby to convert the succession of difference amplitude values into a corresponding succession of amplitude values, each representing sound amplitude during a sample period of a unary digital audio signal.

19. A method according to claim 18, wherein the difference amplitude values are integers of positive, negative or zero value, the start value is zero, and the succession of difference amplitude values initiates with a amplitude value that represents sound amplitude during an initial sample period of the unary digital audio signal.

20. A method according to claim 19, wherein the difference amplitude values are represented by a sign bit and a plurality of data bits, with the difference amplitude value for each sample corresponding to the number of data bits which are set in each plurality of data bits.

21. A method according to claim 20, wherein the data bits of each sample which are set are grouped into a continuous pulse in the compressed signal, the width of which represents the change in the number of active speaker elements of a unary digital loudspeaker in comparison to the immediately preceding sample period.

22. A method according to claim 20, wherein the amplitude values in the decoded signal are represented by a plurality of data bits, with the amplitude value for each sample corresponding to the number of data bits which are set in each plurality of data bits.

23. A method according to claim 22, wherein the data bits of each sample which are set in the decoded signal are grouped into a continuous pulse, the width of which represents the number of speaker elements of a unary digital loudspeaker that are to be active in the sample period concerned.

24. A method according to claim 23, further comprising:

receiving a volume value associated with said succession of difference amplitude values and multiplying each of the difference amplitude values by the volume value prior to a said adding.

25. A decoder for de-compressing a compressed digital audio signal, the decoder comprising:

(a) a decoder input for receiving a digital audio signal containing a succession of difference amplitude values, each representing a difference in sound amplitude between sample periods;

(b) a logic unit having a first input connected to receive the digital audio signal from the decoder input and a second input connected by a feedback path to an output of the logic unit so that the logic unit is operative to increment or decrement the positive amplitude value output by the logic unit in an immediately preceding sample period by the positive or negative difference amplitude value received at its first input; and

(c) a decoder output connected to the output of the logic unit, thereby to output a succession of amplitude values representing sound amplitudes during respective sample periods of a unary digital audio signal, as reconstituted by the logic unit.

26. A decoder according to claim 25, further comprising:

(d) a multiplier arranged between the decoder input and the logic unit, and operable to multiply each difference amplitude value by a volume value supplied to the decoder as part of the compressed digital audio signal.

27. A decoder according to claim 26, further comprising a further multiplier arranged between the logic unit and the decoder output, and operable to multiply each amplitude value by an amount defined by an external actuation signal supplied to the further multiplier.

28. A receiver or wireless receiver comprising a decoder according to claim 27.

29. An audio reproduction system comprising a decoder according to claim 27 in combination with a drive circuit and a unary loudspeaker.