38 CHAPTER 2: S YSTEM SETTINGSCodec Selection It is important to remember not to select a codec based on compressionalone. Consider the trade-off between audio quality and bandwidth use.System-Wide AudioFor system-wide audio, base the default list order on audio quality:VTL Calls AudioFor Virtual Tie Line (VTL) audio, base the default list order on bandwidthusage:G.722G.722.2G.722.2LBWideband AudioG.722.2 is an ITU-T standard for wideband voice applications andservices. G.722.2 is an adaptive multi-rate wideband codec thatuses bit rates ranging from 6.6 to 23.85 kbps.G.722 is an SB-ADPCM (sub band Adaptive Pulse CodeModulation) codec. It runs ADPCM on both the low band (0 -4000 Hz) and the high band (4000 - 8000). The raw bit rate(without network packet headers) is 64 kbps.G.722.2 is a CELP (code excited linear prediction) based codec.G.722 is a 23.85 kbps rate. G.722.2 LB has a rate of 8.85 kbps.The standard was originally designed for wireless networks andthe different rates allow for adapting to varying channelconditions.Table 7 Supported CodecsCodec DescriptionTable 8 Default Order List Based on Audio QualityCodec Quality BandwidthG.722.2 best quality medium bandwidthG.722 high quality high bandwidthG.711 good quality high bandwidthG.722.2LB good quality low bandwidthG.729 medium quality low bandwidthADPCM low quality medium bandwidthTable 9 Default Order List Based on Bandwidth UsageCodec Quality BandwidthG.722.2LB good quality low bandwidthG.729 medium quality low bandwidth
