[ntp:questions] Accuracy of audio tones via VOIP

Robert Scott no-one at notreal.invalid
Tue Jul 9 19:25:34 UTC 2013


On Tue, 09 Jul 2013 18:59:05 +0100, David Woolley
<david at ex.djwhome.demon.invalid> wrote:

>On 09/07/13 15:35, Robert Scott wrote:
>
>> as much as the local quartz oscillator frequencies?  Does anyone have
>> any insight on how Skype and other VOIP systems manage record/playback
>> rate synchronization?
>>
>
>The workings of Skype are a trade secret.  Other ones will have a jitter 
>buffer, and will typically dump or repeat frames if that gets too full 
>or risks underflowing.  RTP allows the source to mark good places to do 
>this.

That does not sound too encouraging for the pitch accuracy of tones
transmitted over Skype.  Of course you would never notice it in normal
speech, which is, I guess, all that Skype is targetting.  But for
calibrating to the standard frequency tones from NIST (500 Hz and 600
Hz), it probably is not trustworthy, right?



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