Digital Sound

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Compression

For various reasons audio data does not easily yield high compression rates when standard textual compression methods are employed. The CD Audio standard (PCM) is commonly termed linear PCM since it performs no compression, storing each value as a separate 16-bit value.

Because sampled sound will differ little from one fraction of a second sample to the next the DPCM (Differential PCM) technique is widely used. DPCM only stores a measurement of the difference between the last sample and the next. Since this difference tends to be small, less bits are required to store the difference values.

The Compact Disc-Interactive format uses ADPCM (Adaptive DPCM), to achieve better compression. ADPCM increases and decreases the magnitude that the difference values represent as the sound signal amplitude changes.