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Question : Which is better G711 alaw, or GSm codecs
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I was using on Asterisk 1.6 GSM codec, but I ntoiced that I can not do DTMF inband, so I changed the codec to G711 alaw, and I have noticed a noticeable latency in voice in internal calls (about 5-7 seconds), any advice to avoide this latency? I am using softphone applications on iPhones. Both connections are done over the internet. The dialplan for the internal calls is: exten => _[2-9]XXX,1,Dial(SIP/${EXTEN},30,tTr) exten => _[2-9]XXX,n,GotoIf($[${DIALSTATUS}=NOANSWER]?noans) exten => _[2-9]XXX,n,GotoIf($[${DIALSTATUS}=BUSY]?busy) ; ; Gets to here is call failed for reason other than no-answer or busy exten => _[2-9]XXX,n,Voicemail(${EXTEN},u) exten => _[2-9]XXX,n,Hangup ; ; This is for ring-no-answer exten => _[2-9]XXX,n(noans),Voicemail(${EXTEN},u) exten => _[2-9]XXX,n,Hangup ; ; This is for busy exten => _[2-9]XXX,n(busy),Voicemail(${EXTEN},b) exten => _[2-9]XXX,n,Hangup Any help please?
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Answer : Which is better G711 alaw, or GSm codecs
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Ashraf,
Sorry for the late response. ulaw and alaw work the same way: sample audio at 8KHz and with low frequency plus anti-alias filters you get a frequency response of 300Hz to 3400Hz. alaw audio is sampled with a 13 bit resolution while ulaw use 14 bit resolution. this is why i tend to think it's a better choice. but in the end, they logarithmically compress amplitudes down to 8 bits. And 8 bits at 8KHz equals 64kbit bandwidth: same for both! My mistake about 'wav', this is not a codec but a file format!
* Have you noticed changes in the latency with various codecs ? * Are you running your PBX in a virtual environment ? If not, what are the specs of your server, and the average CPU utilization ? * Does the latency occur even with just 1 IP phone connected ?
Thanks.
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