Method and apparatus for encoding, decoding and compression of audio-type data

• US 5,625,746 A
• Filed: 02/23/1995
• Issued: 04/29/1997
• Est. Priority Date: 01/17/1992
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Lim, Jae S.
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): GROVER, JOHN M
• Application Number:
  US08/392,573
• Time in Patent Office: 796 Days
• Field of Search: 395/2.38, 395/2.39, 395/2, 395/2.12, 395/2.14, 395/2.2, 395/2.36, 381/30, 381/36, 381/37
• US Class Current: 704/200.1
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 2021/02163 Only one microphone
• CPC Class Codes: G10L 25/27 characterised by the analysis technique
• CPC Class Codes: H04B 1/667 using a division in frequency subbands for TV signals H04N19/63

Abstract

An audio-type signal is encoded. The signal is first divided into bands. For each band, a yardstick signal element is selected. Its magnitude is quantized using a first level of accuracy. This magnitude is used for various purposes, including assigning bits to the different bands, and for establishing reconstruction levels within a band. The magnitude of non-yardstick signal elements is quantized with less accuracy than are the yardstick signal elements. The encoded signal is also decoded. Apparatus for both encoding and decoding are also disclosed. The location of the yardstick element within its band may also be recorded and encoded, and used for efficiently allocating bits to non-yardstick signal elements.

Claims

1. A method for encoding a selected signal element of a signal that is defined by signal elements that are discrete in at least one dimension, said method comprising the steps of:

a. dividing the signal into a plurality of bands, at least one band having a plurality of adjacent signal elements;

b. in each band, identifying a signal element having the greatest magnitude of any signal element in said band, and designating said signal element as a "yardstick" signal element for said band;

c. quantizing the magnitude of each yardstick signal element to a first degree of accuracy;

d. allocating to said selected signal element a signal element bit allocation that is a function of the quantized magnitudes of said yardstick signal elements, said signal element bit allocation chosen such that quantization of said selected signal element using said signal element bit allocation is to a second degree of accuracy, which is less accurate than said first degree of accuracy.

2. The method of encoding of claim 1, further comprising the step of quantizing the magnitude of said selected signal element to a second degree of accuracy that is less accurate than said first degree of accuracy.

3. The method of claim 2, further comprising, before said step of allocating said signal element bit allocation, the step of specifying the location of said respective yardstick signal element within its band with respect to said at least one dimension in which said signal elements are discrete and where said function applied during said step of allocating said bit allocation is further based on the location of said selected signal element within said respective band relative to the location of said respective yardstick signal element.

4. The method of claim 3, said function applied during said step of allocating said bit allocation to said selected signal element further being such that bits are allocated to said selected signal element more preferentially if the location of said selected signal element is closer to the location of said respective yardstick signal element, than bits are allocated if the location of said signal element is farther from the location of said respective yardstick signal element.

5. The method of claim 2, said step of quantizing the magnitude of said selected signal element comprising the step of specifying a plurality of non-yardstick reconstruction levels, said plurality being divided within a range based on the magnitude of said yardstick signal element of said respective band.

6. The method of claim 1, further comprising the step, before said step of dividing said signal into a plurality of bands, the step of transforming said signal from a first domain into another domain, such that said signal is defined by a different set of signal elements that are discrete in at least one dimension, all of said subsequent steps being performed with respect to said transformed signal defined by said different set of signal elements.

7. The method of claim 1, further comprising the step of arranging said yardstick signal elements into an ordered set and transforming said set of yardstick signal elements from a first yardstick domain into another yardstick domain, such that said set is defined by a set of transformed-signal elements.

8. The method of claim 1, further comprising, before said step of allocating a signal element bit allocation, the step of:

for said band including said selected signal element, allocating to said band from the total available number of bits N, a band bit allocation that is a function of;

a. the available remaining number of bits;

b. the number of signal elements in said band and the quantized magnitude of said respective yardstick signal element; and

c. for every other band;

i. the number of signal elements in said other band; and

ii. the quantized magnitude of the respective yardstick signal element for said other band.

9. A method for encoding a signal that is defined by signal elements that are discrete in at least one dimension, said method comprising the steps of:

a. dividing the signal into a plurality of bands, at least one band having a plurality of adjacent signal elements;

b. In each band, identifying a signal element having the greatest magnitude of any signal element in said band, and designating said signal element as a "yardstick" signal element for said band;

c. quantizing the magnitude of each yardstick signal element to a first degree of accuracy;

d. for at least one non-yardstick signal element, allocating a non-yardstick signal element bit allocation that is a function of the quantized magnitudes of said yardstick signal elements, said signal element bit allocation being chosen such that quantization of said at least one non-yardstick signal element using said signal element bit allocation is to a second degree of accuracy, which is less accurate than said first degree of accuracy.

10. The method of encoding of claim 9, further comprising for each said at least one non-yardstick signal element, the step of quantizing the magnitude of said non-yardstick signal element to said second degree of accuracy that is less accurate than said first degree of accuracy.

11. The method of claim 10, further comprising, before said step of allocating said band bit allocation, the step of specifying the location of said respective yardstick signal element with respect to at least one dimension within its band and said function applied during said step of allocating said bit allocation further being based on the relative location of each said at least one non-yardstick signal element within said respective band to the location of said respective yardstick signal element.

12. A method for decoding a code representing a selected signal element of a signal that is defined by signal elements that are discrete in at least one dimension, which has been encoded by a method comprising the steps of:

a. dividing the signal into a plurality of bands, at least one band having a plurality of adjacent signal =elements, one of said bands including said selected signal element;

b. in each band, identifying a signal element having the greatest magnitude of any signal element in said band, and designating said signal element as a "yardstick" signal element for said band;

c. quantizing the magnitude of each yardstick signal element to a first degree of accuracy;

d. allocating to said selected signal element a signal element bit allocation that is a function of the quantized magnitudes of said yardstick signal elements, said signal element bit allocation chosen such that quantization of said selected signal element using said signal element bit allocation is to a second degree of accuracy, which is less than said first degree of accuracy; and

e. quantizing the magnitude of said selected signal element to a second degree of accuracy that is less than said first degree of accuracy and providing a codeword for said quantized selected signal element;

said method of decoding comprising the step of translating said codeword based on a function of the quantized magnitudes of said yardstick signal elements that is appropriately inversely related to said function of the quantized magnitudes used to allocate bits to said selected signal element.

13. The method of decoding of claim 12, said step of translating said digital codeword into a reconstructed signal element comprising the steps of:

receiving all of said quantized yardstick signal elements and translating said signal element codeword in light of said signal element bit allocation function.

14. The method of decoding of claim 13, said method of encoding having further included, before said step of dividing said signal into a plurality of bands, the step of transforming said signal from a first domain into another domain, such that said signal is defined by a second set of signal elements that are discrete in at least one dimension, all of said subsequent steps being performed with respect to said transformed signal defined by said second set of signal elements, said decoding method further comprising, after said step of translating said digital codeword into a reconstructed signal element, the step of applying an inverse transform to said reconstructed signal element to transform said signal element into said original domain.

15. The method of decoding of claim 14, said method of encoding having further included, the steps of:

a. arranging said yardstick signal elements into an ordered set;

b. transforming said set of yardstick signal elements from a first yardstick domain into another yardstick domain, such that said set is defined by a set of transformed-signal elements; and

c. assigning a yardstick digital codeword to each said transformed and quantized yardstick signal element;

said method of decoding further comprising, before said step of translating said signal element codeword in light of said signal element bit allocation function and said band bit allocation function, the steps of;

a. translating said yardstick digital codewords into transformed yardstick signal elements; and

b. applying a transformation to said transformed yardstick signal elements to transform them into said first yardstick domain.

16. A method for decoding a code representing a signal that is defined by signal elements that are discrete in at least one dimension, said signal having been encoded by a method comprising the steps of:

a. dividing the signal into a plurality of bands, at least one band having a plurality of adjacent signal elements;

b. In each band, identifying a signal element having the greatest magnitude of any signal element in said band, and designating said signal element as a "yardstick" signal element for said band;

c. quantizing the magnitude of each yardstick signal element to a first degree of accuracy;

d. for at least one non-yardstick signal element allocating a non-yardstick signal element bit allocation that is a function of the quantized magnitudes of said yardstick signal elements, said signal element bit allocation being chosen such that quantization of said at least one non-yardstick signal element using said signal element bit allocation is to a second degree of accuracy, which is less than said first degree of accuracy; and

e. for each said at leasat one non-yardstick signal element, quantizing the magnitude of said non-yardstick signal element to a second degree of accuracy that is less than said first degree of accuracy and providing a codeword for said quantized non-yardstick signal element;

said method of decoding comprising the steps of translating each said codeword based on a function of the quantized magnitudes of said yardstick signal elements that is appropriately inversely related to said function of the quantized yardstick magnitudes used to allocate bits to said selected signal element.

17. An apparatus for encoding a selected signal element of a signal that is defined by signal elements that are discrete in at least one dimension, said apparatus comprising:

a. means for dividing the signal into a plurality of bands, at least one band having a plurality of adjacent signal elements, one of said bands including said selected signal element;

b. means for identifying, in each band, a signal element having the greatest magnitude of any signal element in said band, and designating said signal element as a "yardstick" signal element for said band;

c. means for quantizing the magnitude of each yardstick signal element to a first degree of accuracy;

d. means for allocating to said selected signal element a signal element bit allocation that is a function of the quantized magnitudes of said yardstick signal elements, said signal element bit allocation chosen such that quantization of said selected signal element using said signal element bit allocation is to a second degree of accuracy, which is less than said first degree of accuracy.

18. The encoding apparatus of claim 17, further comprising:

for said band including said selected signal element, means for allocating to said band from the total available number of bits N, a band bit allocation that is a function of;

a. the available remaining number of bits;

b. the number of signal elements in said band and the quantized magnitude of said respective yardstick signal element; and

c. for every other band;

i. the number of signal elements in said other band; and

ii. the quantized magnitude of the respective yardstick signal element for said other band.

19. An apparatus for decoding a codeword representing a selected signal element of a signal that is defined by signal elements that are discrete in at least one dimension, which has been encoded by a method comprising the steps of:

a. dividing the signal into a plurality of bands, each band having a plurality of adjacent signal elements, one of said bands including said selected signal element;

b. In each band, identifying a signal element having the greatest magnitude of any signal element in said band, and designating said signal element as a "yardstick" signal element for said band;

c. quantizing the magnitude of each yardstick signal element to a first degree of accuracy;

d. allocating to said selected signal element a signal element bit allocation that is a function of the the quantized magnitudes of said yardstick signal elements, said signal element bit allocation chosen such that quantization of said selected signal element using said signal element bit allocation is to a second degree of accuracy, which is less than said first degree of accuracy; and

e. quantizing the magnitude of said selected signal element to a second degree of accuracy that is less than said first degree of accuracy and providing a codeword for said quantized selected signal;

said decoding apparatus comprising means for translating said codeword based on a function of the quantized magnitudes of said yardstick signal elements that is appropriately inversely related to said function of the quantized magnitudes used to allocate bits to said selected signal element.

20. A method for encoding a selected aspect of a signal that is defined by signal elements that are discrete in at least one dimension, said method comprising the steps of:

a. dividing the signal into a plurality of bands, at least one band having a plurality of adjacent signal elements;

b. In each band, identifying a signal element having the greatest magnitude of any signal element in said band, and designating said signal element as a "yardstick" signal element for said band;

c. quantizing the magnitude of each yardstick signal element to a first degree of accuracy;

d. allocating to selected non-yardstick signal elements a signal element bit allocation that is a function of the quantized magnitudes of said yardstick signal elements, said signal element bit allocation chosen such that quantization of said selected signal element using said signal element bit allocation is to a second degree of accuracy, which is less than said first degree of accuracy; and

e. using said accurately quantized magnitude of said yardstick signal elements to encode said selected aspect of said signal.

21. The method of encoding of claim 20, said step of using said quantized magnitude of said yardstick signal element comprising the step of allocating to a selected signal element a signal element bit allocation that is a function of the quantized magnitudes of said yardstick signal elements.

22. The method of encoding of claim 21, further comprising the step of quantizing the magnitude of said selected signal element to a second degree of accuracy that is less accurate than said first degree of accuracy.

23. The method of encoding of claim 22, said step of quantizing the magnitude of said selected signal element comprising the step of specifying a plurality of non-yardstick reconstruction levels, said plurality being divided within a range based on the magnitude of said yardstick signal element of said respective band.

24. A method for decoding a code representing a selected aspect of a signal that is defined by signal elements that are discrete in at least one dimension, which has been encoded by a method comprising the steps of:

a. dividing the signal into a plurality of bands, at least one band having a plurality of adjacent signal elements, one of said bands including said selected signal element;

b. In each band, identifying a signal element having the greatest magnitude of any signal element in said band, and designating said signal element as a "yardstick" signal element for said band;

c. quantizing the magnitude of each yardstick signal element to a first degree of accuracy;

d. allocating to selected non-yardstick signal elements a signal element bit allocation that is a function of the quantized magnitudes of said yardstick signal elements, said signal element bit allocation chosen such that quantization of said selected signal element using said signal element bit allocation is to a second degree of accuracy, which is less than said first degree of accuracy; and

e. using said accurately quantized magnitude to encode said selected aspect of said signal; and

said method of decoding comprising the step of translating said encoded aspect of said signal based on a function of the quantized magnitudes of said yardstick signal elements that is appropriately inversely related to said function of the quantized magnitudes used to encode said selected aspect of said signal.

25. The method of decoding of claim 24, said step in said method of encoding of using said quantized magnitude of said yardstick signal element having further comprised the step of allocating to a selected signal element a signal element bit allocation that is a function of the quantized magnitudes of said yardstick signal elements,

said step of translating being further based on a function of said signal element bit allocation.

26. The method of decoding of claim 25, said step of quantizing the magnitude of said selected signal element further having comprised the step of specifying a plurality of non-yardstick reconstruction levels, said plurality being divided within a range based on the magnitude of said yardstick signal element of said respective band;

said step of translating being further based on a function of said non-yardstick reconstruction levels.

27. A method for encoding a selected signal element of a signal that is defined by signal elements that are discrete in at least one dimension, said method comprising the steps of:

a. dividing the signal into a plurality of bands, at least one band having a plurality of adjacent signal elements;

b. In at least one band, identifying a signal element having the greatest magnitude of any signal element in said band, and designating said signal element as a "yardstick" signal element for said band;

c. quantizing the magnitude of each yardstick signal element to a first degree of accuracy;

d. allocating to said selected signal element a signal element bit allocation that is a function of the quantized magnitudes of said yardstick signal elements, said signal element bit allocation chosen such that quantization of said selected signal element using said signal element bit allocation is to a second degree of accuracy, which is less than said first degree of accuracy.

28. A method for decoding a code representing a selected signal element of a signal that is defined by signal elements that are discrete in at least one dimension, which has been encoded by a method comprising the steps of:

a. dividing the signal into a plurality of bands, at least one band having a plurality of adjacent signal elements, one of said bands including said selected signal element;

b. In at least one band, identifying a signal element having the greatest magnitude of any signal element in said band, and designating said signal element as a "yardstick" signal element for said band;

c. quantizing the magnitude of each yardstick signal element to a first degree of accuracy;

d. allocating to said selected signal element a signal element bit allocation that is a function of the quantized magnitudes of said yardstick signal elements, said signal element bit allocation chosen such that quantization of said selected signal element using said signal element bit allocation is to a second degree of accuracy, which is less than said first degree of accuracy; and

e. quantizing the magnitude of said selected signal element to a second degree of accuracy that is less than said first degree of accuracy and providing a codeword for said quantized selected signal element;

said method of decoding comprising the step of translating said codeword based on a function of the quantized magnitudes of said yardstick signal elements that is appropriately inversely related to said function of the quantized magnitudes used to allocate bits to said selected signal element.