Re: [codec] #16: Delay factor: algorithmic delay vs. transmission latency.

"Christian Hoene" <> Sun, 16 May 2010 08:59 UTC

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From: Christian Hoene <>
To: 'Koen Vos' <>
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Date: Sun, 16 May 2010 10:59:15 +0200
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Subject: Re: [codec] #16: Delay factor: algorithmic delay vs. transmission latency.
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some recent studies on the speech quality of gateways and IP phones are present in
Please have a look at the document first...

At the first glance, I did see evidence for the 3x factor for IP gateways. The best in class at a 40.4 ms one-way delay for G.711
(20ms packets) and a 54.3 ms delay for G.729 (20ms packets) referring to Tables 4.1 and 4.2. The algorithmic delay of G.729 is 15ms
(5ms lookahead).  Thus, the algorithmic delay was 20ms for G.711 (plus an unknown delay of PLC) and 25ms for G.729. Thus, a factor
of 3 seems to be valid (5msx2,9=53,3-40,4)

In case of IP phones it is not that clear. Actually, I did not fully understand the document. That is 2N and 8N application force?

I bet the experts from HEAD acoustic could bring some light into this discussion and explain, whether they have seen something like
a 3x factor between the algorithmic delay and the final latency.

For, we could officially send a liaison statement to ETSI asking for more data.

With best regards,


Dr.-Ing. Christian Hoene
Interactive Communication Systems (ICS), University of Tübingen 
Sand 13, 72076 Tübingen, Germany, Phone +49 7071 2970532

>-----Original Message-----
>From: [] On Behalf Of Koen Vos
>Sent: Sunday, May 16, 2010 10:29 AM
>To: Raymond (Juin-Hwey) Chen
>Subject: Re: [codec] #16: Multicast?
>Quoting "Raymond (Juin-Hwey) Chen":
>> I didn't come up with this 3*(codec frame size) delay number for IP
>> phones myself.  A very senior technical lead in Broadcom's IP phone
>> chips group told me that
>- You've presented no satisfactory explanation for your theory
>- Nor any verifiable empirical evidence
>- It comes from an anonymous source
>- It has changed over time (going from 5x to 3x)
>- It goes against accepted wisdom
>So I'd say the burden of proof is on you..
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