ZyXEL GS-105I User Guide - Page 247
Voice Activity Detection/Silence Suppression
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Chapter 21 VoIP • G.726 is an Adaptive Differential PCM (ADPCM) waveform codec that uses a lower bitrate than standard PCM conversion. ADPCM converts analog audio into digital signals based on the difference between each audio sample and a prediction based on previous samples. The more similar the audio sample is to the prediction, the less space needed to describe it. G.726 operates at 16, 24, 32 or 40 kbps. • G.729 is an Analysis-by-Synthesis (AbS) hybrid waveform codec that uses a filter based on information about how the human vocal tract produces sounds. G.729 provides good sound quality and reduces the required bandwidth to 8 kbps. Voice Activity Detection/Silence Suppression Voice Activity Detection (VAD) detects whether or not speech is present. This lets the Zyxel Device reduce the bandwidth that a call uses by not transmitting "silent packets" when you are not speaking. Comfort Noise Generation When using VAD, the Zyxel Device generates comfort noise when the other party is not speaking. The comfort noise lets you know that the line is still connected as total silence could easily be mistaken for a lost connection. Echo Cancellation G.168 is an ITU-T standard for eliminating the echo caused by the sound of your voice reverberating in the telephone receiver while you talk. MWI (Message Waiting Indication) Enable Message Waiting Indication (MWI) enables your phone to give you a message-waiting (beeping) dial tone when you have a voice message(s). Your VoIP service provider must have a messaging system that sends message waiting status SIP packets as defined in RFC 3842. Custom Tones (IVR) IVR (Interactive Voice Response) is a feature that allows you to use your telephone to interact with the Zyxel Device. The Zyxel Device allows you to record custom tones for the Early Media and Music On Hold functions. The same recordings apply to both the caller ringing and on hold tones. Table 106 Custom Tones Details LABEL DESCRIPTION Total Time for All Tones 900 seconds for all custom tones combined Maximum Time per Individual 180 seconds Tone Total Number of Tones Recordable 5 You can record up to 5 different custom tones but the total time must be 900 seconds or less. Recording Custom Tones Use the following steps if you would like to create new tones or change your tones: PX7511-B0 User's Guide 247