Hybrid audio encoder and hybrid audio decoder which perform coding or decoding while switching between different codecs

摘要

A new hybrid audio decoder and a new hybrid audio encoder having block switching for speech signals and audio signals are provided. Currently, very low bitrate audio coding methods for speech and audio signals are proposed. These audio coding methods cause very long delays. Generally, in coding an audio signal, an algorithm delay tends to be long to achieve higher frequency resolution. In coding a speech signal, the delay needs to be reduced because the speech signal is used for telecommunication. To balance fine coding quality for speech and audio input signals with very low bitrate, a combination of a low delay filter bank like AAC-ELD and a CELP coding method is provided.

主权项

1. A hybrid audio decoder configured to decode a coded stream while switching between a speech coding mode in which linear prediction coefficients are used and an audio coding mode in which a low delay orthogonal transform is used, the hybrid audio decoder comprising:
a processor; and storage coupled to the processor, wherein the processor is configured to perform: low delay decoding for decoding a coded signal in the audio coding mode using an inverse modified discrete cosine transform filter bank; generating of a synthesized signal based on the low delay decoding; audio decoding for decoding, in the speech coding mode, a coded signal including the linear prediction coefficients; generating of an audio synthesized signal based on the audio decoding; decoding of a signal of a portion of a current frame to be decoded, using a signal of a previous frame preceding the current frame; and combining of the decoded signal of the portion of the current frame and the audio synthesized signal of another portion of the current frame, to reconstruct a signal of the current frame, when the current frame is a frame to be decoded immediately before the audio coding mode is switched to the speech coding mode, wherein, in the low delay decoding, an extended frame is windowed in a plurality of short windows each having a shorter length than a frame, and the inverse modified discrete cosine transform filter bank is applied to the extended frame, the extended frame being generated by combining the current frame and the previous frame.