TRANSFORM CODER AND TRANSFORM CODING METHOD

• US 20090281811A1
• Filed: 10/13/2006
• Published: 11/12/2009
• 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
• Granted Patent: US 8,135,588 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• 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 (123) are outputted one by one, and an error signal is generated by subjecting the candidate and scale factors outputted from scale factor computing sections (121, 122) to a predetermined operation. A judging section (126) determines a weight vector given to a weighted error computing section (127) depending on the sign of the error signal. The weighted error computing section (127) computes the square of the error signal, multiplies the square of the error signal by the weight vector given from the judging section (126), and computes a weighted squared error E. A search section (128) 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 calculating section that calculates a plurality of input scale factors associated with an input spectrum;

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

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

a weighted distortion calculating section that calculates weighted distortion such that the distortion of when the one of the plurality of input scale factors is smaller than the scale factor outputted from the codebook, is added more weight than the distortion of when the one of the plurality of input scale factors is greater than the scale factor outputted from the codebook; and

a searching section that searches for a scale factor that minimizes the weighted distortion in the codebook.

2. The transform coding apparatus according to claim 1, further comprising a determining section that adaptively determines a number of bits assigned in encoding of the input scale factors,

wherein the weighted distortion calculating section calculates weighted distortion using the weight with more weight, with respect to an input scale factor assigned a smaller number of bits.

3. The transform coding apparatus according to claim 1, further comprising a background noise detecting section that detects whether or not the input spectrum contains noise,

wherein the weighted distortion calculating section adds more weight to the distortion of when the one of the plurality of input scale factors is smaller than the scale factor outputted from the codebook 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, and calculates the weighted distortion such that less weight is applied as a level of background noise detected in the background noise detecting section increases.

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

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

4. A transform coding apparatus comprising:

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

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

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

a multiplying section that multiplies the one of the plurality of first scale factors by the correcting coefficient outputted from the codebook and outputting the one of the plurality of first scale factors;

a distortion calculating section that calculates distortion between one of the plurality of second scale factors and the first scale factor outputted from the multiplying section;

a weighted distortion calculating section that calculates weighted distortion such that the distortion of when the one of the plurality of the second scale factor is smaller than the first scale factor outputted from the multiplying section is added more weight than the distortion of when the one of the plurality of the second scale factor is greater than the first scale factor outputted from the multiplying section; and

a searching section that searches for a correcting coefficient that minimizes the weighted distortion in the codebook.

5. The transform coding apparatus according to claim 4, further comprising a similarity calculating section that calculates a similarity between the first spectrum and the second spectrum,

wherein the weighted distortion calculating section calculates weighted distortion using the weight with more weight, with respect to a second scale factor of a lower similarity.

6. The transform coding apparatus according to claim 4, further comprising a background noise detecting section that detects whether or not one or both of the first spectrum and the second spectrum contain noise,

wherein the weighted distortion calculating section adds more weight to the distortion of when the one of the plurality of second factors is smaller than the first scale factor outputted from the multiplying section than to the distortion of when the one of the plurality of second scale factors is greater than the first scale factor outputted from the multiplying section, and calculating the weighted distortion such that less weight is applied as a level of background noise detected in the background noise detecting section increases.

9. A transform coding method comprising:

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

selecting one of a plurality of scale factors from a codebook that stores the plurality of scale factors;

calculating distortion between the one of the plurality of input scale factors and the selected scale factor;

calculating weighted distortion such that the distortion of when the one of the plurality of the input scale factors is smaller than the selected scale factor, is added more weight than the distortion of when the one of the plurality of the input scale factors is greater than the selected scale factor; and

searching for a scale factor that minimizes the weighted distortion in the codebook.

10. A transform coding method comprising:

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

selecting one of a plurality of scale factors from a codebook that stores the plurality of scale factors;

detecting whether or not the input spectrum contains noise;

calculating distortion between the one of the plurality of input scale factors and the selected scale factor;

adding more weight to the distortion of when the one of the plurality of input scale factors is smaller than the selected scale factor than to the distortion of when 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; and

searching for a scale factor that minimizes the weighted distortion in the codebook.