This article defines the recording voice format and the location to choose the correct format/codec?
When a call is recorded to a voice/audio file, the recording is encoded using a specific codec (enCODing DECoding). The two most popular recording codecs are G.711 m-law and G.711 a-law and provide the highest sound quality but consume disk space at the rate of 8KB per second. The GSM 6.10 option consumes less disk space than the the G.711 codecs but has a slightly lower sound quality. Recording in GSM will also increase the CPU load when compared to G.711.