[LAU] audio latency question

andy baxter andy at earthsong.free-online.co.uk
Sun Mar 20 18:56:37 UTC 2011


On 20/03/11 18:38, Jörn Nettingsmeier wrote:
> On 03/20/2011 06:25 PM, andy baxter wrote:
>> Hi,
>>
>> I am thinking about a possible design for the second version of the
>> position sensing drum pad I have been working on, and I have a question
>> about latency. I am working around the assumption that 10ms latency is
>> about the worst it can get before people start to notice it in practice,
>> so I am thinking of building the pad in a way where the normal latency
>> is about 1ms, but it degrades to between 10-15 ms in the very worst case
>> (many simultaneous strikes and pressure variations across the pad).
>> Allowing this level of degradation would make it possible (I think) to
>> use an arduino rather than a faster processor, which would be nice.
>
> a drummer will get very grumpy indeed over latencies in the 10ms 
> range. (i understand your use of the term to mean "time it takes for 
> the sound to come out after the drummer has hit the pad").
>

Yes that's what I meant.

> you should aim for 2ms or less, which takes considerable effort and a 
> very good sound card.
>
> but if you can't do that, then by all means keep the latency constant. 
> shifting latency will make the the drummer eat his sticks, or worse 
> yet, direct random acts of violence against other people, possibly 
> even you.
>
> just imagine you are playing a constant 16th note pattern at 120 bpm.
>
> one beat will be 0.125 seconds.
> say your second beat is delayed by 10ms ue to jittery time, and the 
> next one is dead on again. the groove will appear to "swing" in weird 
> ways. real swing would mean 0.167s, then 0.083s, so that's 
> considerably more, but to keep a groove going, the drummer has to keep 
> such times very accurately, and 10ms is a major earthquake to a 
> flowing groove, especially since the drummer's physical feel and the 
> acoustic result do not match when your software jitters.
> even when the following beats are all delayed by 10ms because your 
> application scheduler has now entered its high-load steady state, the 
> drummer will hear a drag, try to speed up to compensate, and oscillate 
> around the correct time for a number of beats. this ruins the feel and 
> i could imagine it could even cause physical harm due to dysfunctional 
> use of muscles.
>
> but even when the latency is constant, drummers are used to get very 
> sharp and distinct physical feedback when the stick rebounds from the 
> drum head, and they are very close to the instrument. so they will 
> usually be a lot less tolerant than electric guitarists (who are used 
> to operate at 3 or 4 m distance from their amps or monitor speakers) 
> or (extreme example) church organists, who can learn to deal with tens 
> or even hundreds of milliseconds of latency (plus a dragging 
> congregation choir on top) :-D
>

OK - thanks for pointing this out.


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