[linux-audio-user] emu10k1 and jack

Antonio debianuser at supereva.it
Wed Feb 4 06:24:48 EST 2004

Robert Jonsson wrote:
> The difference between the two is that timidity probably opens the soundcard 
> with write-only, whereas jack by default opens it read-write (full duplex). 
> The emu10k driver doesn't allow any setting below -p 512 if you run in full 
> duplex. If you change the output of jack so it only writes you could set it 
> lower here too.

You are right! Forcing jack to open alsa in plaback only mode I can set 
a period 256 frames with 2 periods of buffer. I play via midi so I don't 
  need the capture the most of times. So playng with ZynAddSubFX I can 
get a latency of 10 ms! This isn't just a "pretty low latency" but a 
_very_ low latency for me :-). Thanks.

> I think this is a shortcoming of the driver. I've come to understand that the 
> emu10k1 is capable of much lower settings with the kx drivers in windows.

But it's a sad closed (I think almost) personal project. Personally I 
apprecciate a lot those ideas about drivers policy:


don't you?

> Very few cards/drivers support using only one buffer. If I understand things 
> correctly it means that whenever the buffer runs empty the program has to 
> rewrite the buffer _before_ the soundcard needs another single sample. Which 
> is a _very_ short time.
> In practice this setup is unusable. 

ok, I understand

>>The last but not least, I have a general question about jack: if I a
>>stream pass twice or more times into jack (for example alsa in -> jack
>>rack -> ardour -> alsa out, 3 times) does the latency increases twice or
>>more, proportionally, or it is only related to the various apps latency?
> Somebody more knowledgeable than me should answer that :)

I've done the question because I noticed that jamin increase the latency 
much more then other apps (like ardour or jack-rack). For example the 
with the setup:

midi -> ZynAddSubFX -> jack-rack -> ardour -> alsa out
          (5.3 ms)

I have no (at least easily) audible delay when I play (using 2 periods 
of 512 frames), while with:

midi -> ZynAddSubFX -> jamin -> alsa out

I have a strong delay of (I estimate) about 0.1 ~ 0.2 secs, which means 
no realtime response. So I understand that I don't understand something 
about how jack works :-)

Anyway, there is a way to mesure the global in-out latency? (I've tried 
the Benno's latency test, it does the benchmark but does not produce any 
png result, and I think is only a kernel-related test)

 > Not stupid at all. I hope my answers where correct and satisfactory.

Fully satisfactory, you fullfilled all (well quite all ;) my doubts in 
one time! Thanks a lot.

> /Robert


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