[linux-audio-user] emu10k1 and jack
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:
> 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
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.
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