| 摘要 |
An audio codec having an encoder and a decoder is disclosed. The encoder enables the compression of an audio signal for transmission or storage while the decoder receives a compressed audio signal for playback. A time scaling module within the decoder allows variation of the playback rate of the compressed audio signal. Further, no significant depreciation in the quality of pitch occurs as a result of varying the playback rate. The codec features a control for independently varying the playback rate and a module for delivering pitch compensation. The encoder utilizes a sub-band coding scheme (e.g., MPEG-1 and MPEG-2) wherein an audio signal is split into at least two frequency sub-bands for compression. Using a filter bank having two filters, for example, the audio signal is split into the frequency sub-bands. An decoder having a time scaling module is further disclosed. The time scaling module time stretches or compresses an audio signal as desired using a synchronized overlap and add (SOLA) algorithm. The time scaling module includes a processor, an input buffer, and an output buffer. Using SOLA, input and output frames are initially formed within the buffers, and subsequently, the input and output frames are concatenated within a predetermined search range to accomplish time stretching or time compression.
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