Re: [codec] Thresholds and delay.

I agree, I wasn't meaning to propose 500 ms round trip times as the goal.

Stephen Botzko

On Tue, May 11, 2010 at 2:56 PM, Michael Knappe <mknappe@juniper.net> wrote:

> Stephen,
>
> Agreed that achieving low enough latencies for sidetone perception should
> not be a goal of the wg, but we should be aiming if at all possible for
> better than 250 ms one-way delay in typical (and non-tandemed) deployments.
> The knee of the one-way delay impairment factor begins rising non-linearly
> somewhere between 150 and 250 ms.
>
> Mike
>
> ------------------------------
>  *From*: codec-bounces@ietf.org <codec-bounces@ietf.org>
> *To*: Ben Schwartz <bmschwar@fas.harvard.edu>
> *Cc*: codec@ietf.org <codec@ietf.org>
> *Sent*: Tue May 11 14:19:22 2010
> *Subject*: Re: [codec] Thresholds and delay.
> >>>
> In the presence of echo, round-trip delay must be kept below 30 ms to
> ensure that the echo is perceived as sidetone, according to the Springer
> handbook of speech processing:
> >>>
> Though true, I don't think this is a mainstream consideration.
>
> VOIP phones that are capable of speakerphone operation all have acoustic
> echo cancelers, and those cancelers are already tuned to deal with internet
> delays with other voice codecs.  Certainly our phones and videoconferencing
> systems do not have problems with path delays of this order (hundreds of
> milliseconds).
>
> From my own experience (not testing) I agree with Brian's claim that 500 ms
> round trip is acceptable for most conversation.
>
> It does depend on what you are doing, and there are certainly tasks where
> much lower delays are needed.
>
> Regards,
> Stephen Botzko
>
>
>
> On Tue, May 11, 2010 at 2:06 PM, Ben Schwartz <bmschwar@fas.harvard.edu>wrote:
>
>> On Tue, 2010-05-11 at 12:48 -0400, Marshall Eubanks wrote:
>> > As a point of order, I object to any graphs without an available paper
>> > behind them.
>>
>> I have located the first paper mentioned by Christian Hoene at
>> http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=81952
>> but of course it's paywalled.
>>
>> One test in that paper told trained subjects to "Take turns reading
>> random numbers aloud as fast as possible", on a pair of handsets with
>> narrowband uncompressed audio and no echo.  Subjects were able to detect
>> round-trip delays down to 90 ms.  Conversational efficiency was impaired
>> even with round-trip delay of 100 ms.
>>
>> Let me emphasize again that these delays are round-trip, not one-way,
>> there is no echo, and the task, while designed to expose latency, is
>> probably less demanding than musical performance.
>>
>> In the presence of echo, round-trip delay must be kept below 30 ms to
>> ensure that the echo is perceived as sidetone, according to the Springer
>> handbook of speech processing:
>>
>> (
>> http://books.google.com/books?id=Slg10ekZBkAC&lpg=PA83&ots=wc9yM9WrCs&dq=sidetone%20delay%2030%20ms&lr&pg=PA84#v=onepage&q&f=false
>> )
>>
>> Such low delays are clearly impossible on many paths, but for Boston to
>> New York City (or London to Paris), ping times can be less than 18 ms,
>> making echo->sidetone conversion just barely possible for a codec with
>> 5ms frames.
>>
>> I accept Brian Rosen's claim that a slow conversation doesn't normally
>> suffer greatly from round-trip latencies up to 500 ms, but under some
>> circumstances much lower latencies are valuable.  Let's make sure
>> they're achievable for those who can use them.
>>
>> --Ben
>>
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>