Patent ID: 7917369

Claim:
In a transform-based audio encoder, a method of improved band truncation, the method comprising: performing a frequency transform on each of multiple input channels of a multi-channel input audio signal to produce multiple input channels of transform domain coefficients; performing a multi-channel transformation on the multiple input channels of transform domain coefficients for the multi-channel input audio signal to produce a plurality of joint coding channels; on a channel-by-channel basis, selectively suppressing at least one of the joint coding channels as a function of at least quality of reproduction, rate control buffer fullness, and channel separation, wherein the selectively suppressing comprises scaling the at least one joint coding channel by a scaling factor having a value varying based on a current average level of quality, current rate control buffer fullness and amount of channel separation; and for at least one of the joint coding channels: selecting as an open-loop process a first portion of the transform domain coefficients for band truncation as a function of a target quality measurement; suppressing the selected first portion of the transform domain coefficients from encoding in a compressed audio data stream; measuring an achieved quality measurement of the input audio signal encoded with the selected first portion of the transform domain coefficients suppressed; selecting as a closed-loop process a second portion of the transform domain coefficients for second band truncation as a function of the achieved quality measurement; and suppressing the selected second portion of the transform domain coefficients from encoding in a second compressed audio data stream.