MULTI-MODE AUDIO CODEC AND CELP CODING ADAPTED THEREFORE

摘要

In an embodiment, bitstream elements of sub-frames are encoded differentially to a global gain value so that a change of the global gain value results in an adjustment of an output level of the decoded representation of the audio content. Concurrently, the differential coding saves bits. Even further, the differential coding enables the lowering of the burden of globally adjusting the gain of an encoded bitstream. In another embodiment, a global gain control across CELP coded frames and transform coded frames is achieved by co-controlling the gain of the codebook excitation of the CELP codec, along with a level of the transform or inverse transform of the transform coded frames. In another embodiment, the gain value determination in CELP coding is performed in the weighted domain of the excitation signal.

主权项

1. A CELP encoder comprising
a linear prediction analyzer configured to generate linear prediction filter coefficients for a current frame of an audio content and encode the linear prediction filter coefficients into a bitstream; an excitation generator configured to determine a current excitation of the current frame as a combination of an adaptive codebook excitation and an innovation codebook excitation, which, when filtered by a linear prediction synthesis filter based on the linear prediction filter coefficients, recovers the current frame, by constructing the adaptive codebook excitation defined by a past excitation and an adaptive codebook index for the current frame and encoding the adaptive codebook index into the bitstream; and constructing the innovation codebook excitation defined by an innovation codebook index for the current frame and encoding the innovation codebook index into the bitstream; and an energy determiner configured to determine an energy of a version of the audio content of the current frame filtered a weighting filter, to acquire a global gain value and encoding the global gain value into the bitstream, the weighting filter construed from the linear prediction filter coefficients.