.The following table compares the four codecs that the Vivox SDK uses.
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Opus
Siren 14
Siren 7
PCMU
Network Bitrate*
40 kbit/s
32 kbit/s
32 kbit/s
64 kbit/s
CPU Usage (Encoding)
Moderate
Low
Lower
Lowest**
CPU Usage (Decoding)
Low
Low
Lower
Lowest
Supports configurable bitrate?
Yes (6 to 128 kbit/s)
No
No
No
Audio Sample Rateâ€
48 kHz
32 kHz
16 kHz
8 kHz
Audio Quality
Best (20+ kbit/s)
Good
Fair
Poor
* Numbers listed represent the default bitrate for each codec for one voice stream at theoretical max. Codec bitrates are only in effect while speech is active (either being transmitted or received). These exclude 14.4 kbit/s of overhead from Vivox packet headers while speech is active.** PCMU is essentially free in terms of CPU usage. Encoding and decoding are composed of bitwise operations and table lookups.†Higher sample rates allow for higher fidelity audio but do not by themselves guarantee a better sound.