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# Audio Compression

For purposes of efficient storage, media files are often stored in a compressed form. Audio compression often results in a small amount of distortion. The compression algorithms, used in codecs (codec stands for compression–decompression), have been developed over many years to minimize the distortion from a perceptual point of view. In general, when the compression rate increases, so does the distortion. But the newer codecs generally offer less distortion for the same compression rate, compared to the older codecs.

Popular audio codecs used in video are:

- MP2, MP3 (multiple sampling rates)
- WMA (multiple sampling rates)

This table summarizes the telephony codecs and compressed data rates (all sampled at 8 kHz).

Codec | Description | Data rate (Kbps) | Data rate (MB per hour)
--- | --- | --- | ---
Original | Linear 16 bit | 128 | 57.6
G.711 ulaw | Ulaw 8 bit | 64 | 28.8
G.711 linear | Linear 8 bit | 64 | 28.8
G.726 | ADPCM | 32 | 14.4
G.729 | CS-ACELP | 8 | 3.6
GSM 6.10 | CELP | 13 | 6.5
DSP Group Truespeech | ADPCM | 8.5 | 3.8
MP3 | MDCT | Variable | Variable
WMA | MDCT | Variable | Variable

HPE IDOL Speech Server does not support compressed streamed audio, but can support compressed audio files (you must set the `FFmpegDirectory` configuration parameter).

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