Audio Settings 37Audio Settings Audio Settings enable you to affect the network impact of your audiopackets by enabling or disabling compression and silence suppression.You can enable and disable these settings for the entire system and thenoverride the system-wide setting for individual devices.CompressionOverviewBefore voice traffic can be transmitted over a digital network, the audiowaveform, an analog signal, must be encoded into a digital format. Thedigitized audio is packetized and delivered over the network to adestination, and then decoded back into a voice waveform. Softwarecalled a codec (coder/decoder) converts the audio information betweendigital and analog formats.Digitized audio formats have different properties. Each format representsa compromise between bandwidth and audio quality, that is, high qualityaudio typically requires more network bandwidth. Compressing thedigitized audio data can conserve bandwidth with little compromise inaudio quality, but compression requires increased processing overheadwhen encoding and decoding the audio information. Too muchprocessing overhead can introduce delay.Table 7 lists the codecs that the system supports and describes thecharacteristics of each one..Table 7 Supported CodecsCodec DescriptionG.711No CompressionAn International Telecommunications Union (ITU) standard foraudio encoding. Encoding and decoding is fast and support iswidespread. Also called MULAW or μLAW. A-law is a slightvariation, which European telephone systems use. G.711provides high quality audio at 64 kbps. Telephone companiesworldwide use G.711 encoding to provide “toll-quality audio.”ADPCMMediumCompressionAdaptive Differential Pulse Code Modulation (ADPCM) providesgood quality audio at a lower bitrate (32 kbps) than G.711. Thesystem uses the International Multimedia Association (IMA)version of ADPCM.G.729HighCompressionG.729, an ITU standard, employs a more sophisticatedcompression technique than ADPCM and it is supportedworldwide. The G.729A codec compresses the audio informationto 8 kbps, although processing overhead results in actualbandwidths greater than 8 kbps.
