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Re: Repeater latency



At 11:43 AM 7/22/2003, mark wrote:
>On Tuesday, July 22, 2003, at 08:10  AM, Per Boysen wrote:
>>--> Question of latency:
>>I have been playing with a POD 1 and I think it sucks because of the
>>latency. I am also finding the latency in the Repeater hard to coup with
>>when not putting it in a loop to keep the instruments direct signal. Has
>>someone here measured the latency of the POD 1 and the Repeater?
>
>You guys must have amazing powers of perception.  I've never found the 
>Repeater to be awkward to use in terms of latency.

The annoying thing about the Repeater is the direct through audio has a 
noticeable latency. I measured it at 12.5ms on my scope. For me that is 
perceptible, but it may not be for everybody. In use I think I can adapt 
to 
it, but it is annoying since my ears are telling me the sound source is a 
particular distance, yet the extra delay doesn't fit with that.

I could see it being a problem in mixing though, if you have some sources 
going through the Repeater and some not. Either there are phase problems, 
or rhythmic feel problems. If the snare is 12.5ms behind the beat, the 
feel 
of rhythm will be different.

Basically it means the Repeater is passing the direct audio through the 
digital path, and there is some significant buffering going on. The 
Repeater is probably buffering 512 samples, by my rough calculation. That 
seems like a lot to me.

>Back when I as beta testing v. 1.1 of the software, I did a test.  I 
>captured a loop of a drum machine and had them then play together.  I did 
>notice a slight phase shift, but no where near 20ms I'm sure.

that's a test of the sync accuracy, not the direct through audio latency 
which I think is what Per is referring to.

>At that point it starts to sound like a doubling.  I think I read that 
>Kim 
>did a similar test on the EDP and got the similar results.

The echoplex passes direct audio through as analog, and the delay is 
probably more on the order of nanoseconds and imperceptible.

The sync accuracy test for the EDP is pretty dead on, as good as you can 
get with MIDI. The 1.0 software repeater was pretty bad, but I never tried 
that test with 1.1.

Another type of latency is for controls. When you tap the button, how long 
does the device take to react? The EDP is a real-time OS that guarantees 
the function starts within 1.5ms, no matter what else is going on.

>No digital device at this point isn't going to give you some degree of 
>latency, but unless you're putting your signal direct into a tube amp 
>there's going to be some.  A/D-D/A converters take a little time to work 
>and there's the DSP to consider as well.

yes, but all of these things are very dependent on the design. For 
example, 
does direct audio have to go through the digital path at all? In many 
cases 
no. Delay through the convertors will depend on the parts selected. Did 
they choose parts with this in mind? Much more significant delays will 
come 
from buffering samples before passing them out again. Did they optimize 
their system and dsp algorithm design to minimize buffering? These things 
are fundamental design issues that have to be considered from the very 
beginning of the project. In my view, something like a looper that is used 
mainly in real-time performance should give a high priority to these 
issues. The fact that the Repeater ends up with 12.5ms of direct through 
audio delay tells me they didn't.

kim


______________________________________________________________________
Kim Flint                     | Looper's Delight
kflint@loopers-delight.com    | http://www.loopers-delight.com