Transform coder and transform coding method

• US 8,135,588 B2
• Filed: 10/13/2006
• Issued: 03/13/2012
• Est. Priority Date: 10/14/2005
• Status: Active Grant

• Current Assignee: III Holdings 12, LLC (Intellectual Ventures LLC)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Oshikiri, Masahiro, Yamanashi, Tomofumi
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): Borsetti, Greg
• Application Number:
  US12/089,985
• Publication Number:
  US 20090281811A1
• Time in Patent Office: 1,978 Days
• Field of Search: 704/229, 704/230, 704/500
• US Class Current: 704/229
• CPC Class Codes: G10L 19/0208 Subband vocoders
• CPC Class Codes: G10L 19/038 Vector quantisation, e.g. TwinVQ audio
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding

Abstract

A transform coder leading to reduction of degradation of perceptual sound quality even if an adequate number of bits is not assigned. Candidates of a correction scale factor stored in a correction scale factor codebook are outputted one by one, and an error signal is generated by subjecting the candidate and scale factors outputted from scale factor computing sections to a predetermined operation. A judging section determines a weight vector given to a weighted error computing section depending on the sign of the error signal. The weighted error computing section computes the square of the error signal, multiplies the square of the error signal by the weight vector given from the judging section and computes a weighted squared error E. A search section determines the candidates of the correction scale factor which minimizes the weighted squared error E by a closed loop processing.

Claims

1. A transform coding apparatus, comprising:

an input scale factor calculator that calculates a plurality of input scale factors associated with an input spectrum;

a codebook storage that stores a plurality of scale factors and outputs one of the plurality of scale factors;

a distortion calculator that calculates distortion between one of the plurality of input scale factors and the scale factor outputted from the codebook storage;

a weighted distortion calculator that calculates weighted distortion such that the calculated weighted distortion uses a higher weight when the one of the plurality of input scale factors is smaller than the scale factor outputted from the codebook storage, than when the one of the plurality of input scale factors is greater than the scale factor outputted from the codebook storage; and

a searcher that searches for a scale factor that minimizes the weighted distortion in the codebook storage.

2. The transform coding apparatus according to claim 1, further comprising:

a determiner that adaptively determines a number of bits assigned in encoding of the input scale factors,

wherein the weighted distortion calculator calculates weighted distortion using the weight with more weight when an input scale factor is assigned smaller number of bits.

3. The transform coding apparatus according to claim 1, further comprising:

a background noise detector that detects whether or not the input spectrum contains noise,

wherein the weighted distortion calculator uses more weight in the distortion calculation when the one of the plurality of input scale factors is smaller than the scale factor outputted from the codebook storage than to the distortion of when the one of the plurality of input scale factors is greater than the scale factors outputted from the code book storage, and calculates the weighted distortion such that less weight is applied as a level of background noise detected in the background noise detector increases.

4. A communication terminal apparatus, comprising the transform coding apparatus according to claim 1.

5. A base station apparatus, comprising the transform coding apparatus according to claim 1.

6. A transform coding apparatus, comprising:

a first scale factor calculator that calculates a plurality of first scale factors associated with a first spectrum;

a second scale factor calculator that calculates a plurality of second scale factors associated with a second spectrum;

a codebook storage that stores a plurality of correcting coefficients and outputs one of the plurality of correcting coefficients;

a multiplier that multiplies the one of the plurality of first scale factors by the correcting coefficient outputted from the codebook storage and outputting a corrected one of the plurality of first scale factors;

a distortion calculator that calculates distortion between one of the plurality of second scale factors and the corrected first scale factor outputted from the multiplier;

a weighted distortion calculator that calculates weighted distortion such that the calculated weighted distortion uses higher weight when the one of the plurality of the second scale factors is smaller than the corrected first scale factor outputted from the multiplier than when the one of the plurality of the second scale factors is greater than the corrected first scale factor outputted from the multiplier; and

a searcher that searches for a correcting coefficient that minimizes the weighted distortion in the codebook storage.

7. The transform coding apparatus according to claim 6, further comprising:

a similarity calculator that calculates a similarity between the first spectrum and the second spectrum,

wherein the weighted distortion calculator calculates weighted distortion using the weight with more weight when a second scale factor has a lower similarity to the first scale factor.

8. The transform coding apparatus according to claim 6, further comprising:

a background noise detector that detects whether or not one or both of the first spectrum and the second spectrum contain noise,

wherein the weighted distortion calculator uses more weight in the distortion calculation when the one of the plurality of second factors is smaller than the corrected first scale factor outputted from the multiplier than to the distortion when the one of the plurality of second scale factors is greater than the corrected first scale factor outputted from the multiplier, and calculating the weighted distortion such that less weight is applied as a level of background noise detected in the background noise detector increases.

9. A transform coding method, comprising:

calculating, by a calculator, a plurality of input scale factors associated with an input spectrum;

selecting, by a selector, one of a plurality of scale factors from a codebook storage that stores the plurality of scale factors;

calculating, by a calculator, distortion between one of the plurality of input scale factors and the selected scale factor;

calculating, by a calculator, weighted distortion such that the calculated weighted distortion uses higher weight when the one of the plurality of the input scale factors is smaller than the selected scale factor, than when the one of the plurality of the input scale factors is greater than the selected scale factor; and

searching, by a searcher, for a scale factor that minimizes the weighted distortion in the codebook storage.

10. A transform coding method, comprising:

calculating, by a calculator, a plurality of input scale factors associated with an input spectrum;

selecting, by a selector, one of a plurality of scale factors from a codebook storage that stores the plurality of scale factors;

detecting, by a detector, whether or not the input spectrum contains noise;

calculating, by a calculator, distortion between one of the plurality of input scale factors and the selected scale factor; and

searching, by a searcher, for a scale factor that minimizes the weighted distortion in the codebook storage,

wherein the distortion is calculated by using more weight to the distortion when the one of the plurality of input scale factors is smaller than the selected scale factor than when the distortion of the one of the plurality of the input scale factors is greater than the selected scale factor, and calculating weighted distortion such that less weight is applied as a level of background noise detected in the background noise detecting section increases.