Transform coder and transform coding method

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.

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.

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.