[LAD] RME madi latency

[Fokke de Jong]

It turns out I am doing something very wrong, and i *can* get much lower latency’s even with the large buffersize.

I could not get jack_delay itself to work (it wouldn’t connect to any ports no matter what i tried), but 
i did use jack rather than my own alsa implementation and with a period size of 32 samples @ 48KHz I measured a roundtrip delay of around 169 samples (3.5 ms), which is very reasonable.

The method I used was perhaps a bit crude, so it could be off by a few samples. But it seems accurate enough. (I used another soundcard on a different machine, and plugged one output straight back in, and the other went through the converter /madi fx / jack and then back in. The difference in timing should be the rtd).

So now i am a but confused how to get the same kind of latency in my own code (using alsa directly rather than through jack)

Basically what happens is when i have a buffersize of 8192 and a period of 32 is that  snd_pcm_avail_update(capture_handle), will keep returning 0 until i have played back the full 8192 samples. After that I will start receiving input samples, but obviously the latency is  now more than 8182 samples…

How can i make alsa not wait until the entire buffer is full?

best,
Fokke









> On Feb 3, 2016, at 15:40 , Jörn Nettingsmeier <nettings at stackingdwarves.net> wrote:
> 
> On 02/03/2016 02:54 PM, Fokke de Jong wrote:
>> Hi Adrian,
>> 
>> I could’ve guessed you were on this list as well :-)
>> I’m going to try this tomorrow when back in the studio, or maybe I can even do it remote if I have left everything patched up correctly :-)
>> 
>> I will come back with the results.
>> Thanks for your input!
>> 
>> fokke
> 
> watching this with interest, keep us posted about your results and longer-term experience with this card!
> 
> 
> best,
> 
> 
> jörn
> 
> 
> 
> 
> -- 
> Jörn Nettingsmeier
> Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
> 
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> 
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> 
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