Up: Audio Compression
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Traditional lossless compression methods (Huffman, LZW, etc.) usually
don't work well on audio compression (the same reason as in image
The following are some of the Lossy methods applied to audio
- Silence Compression - detect the "silence", similar
to run-length coding
- Adaptive Differential Pulse Code Modulation (ADPCM)
e.g., in CCITT G.721 - 16 or 32 Kbits/sec.
(a) encodes the difference between two consecutive signals,
(b) adapts at quantization so fewer bits are used when the value is
- It is necessary to predict where the waveform is headed -> difficult
- Apple has proprietary scheme called ACE/MACE. Lossy scheme that
tries to predict where wave will go in next sample. About 2:1 compression.
- Linear Predictive Coding (LPC) fits signal to speech model and
then transmits parameters of model. Sounds like a computer talking,
- Code Excited Linear Predictor (CELP) does LPC, but also
transmits error term - audio conferencing quality at 4.8 kbits/sec.