Old 07-23-2018, 09:02 AM   #1
audiojunkie
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Default ALSA vs JACK latency experiences

My understanding is audio apps run with lower latencies with JACK than with ALSA. What has been everyone's experiences with this? My initial testing seemed to confirm this, but I wanted to know what everyone else was experiencing.

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Old 07-23-2018, 09:57 AM   #2
David Else
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I don't think this is the case as JACK runs on top of ALSA. I have not tested myself.
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Old 07-23-2018, 11:19 AM   #3
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Quote:
Originally Posted by David Else View Post
I don't think this is the case as JACK runs on top of ALSA. I have not tested myself.
That's what one would think logically. :-) However, there are several reports of xruns like crazy in ALSA and smooth running under JACK (and surely vice versa as well). It made me think that it may have come down to applications not being specifically "tuned" to work on ALSA, whereas JACK is tuned to work on ALSA, and apps are tuned to work on JACK. That's the only thing I can think of that might cause this. But either way, I'm trying to determine if there is any truth to it, and if Reaper works better in one verses the other.

So, what is everyone's experiences when running in ALSA vs JACK? How low can you get your latency before XRuns when using each technology?
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Old 07-23-2018, 11:37 AM   #4
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Continuing with my research on this topic, I found the following conversation from the Mixxx Community Forums to be interesting:

https://www.mixxx.org/forums/viewtopic.php?f=1&t=460

This seems to indicate that there is NO added latency, which would indicate that JACK itself is at least equal to ALSA latency-wise. I suppose it is still possible for badly behaving apps in the JACK chain to cause latency. And it is also possible, I suppose, that when an app is tuned better for a particular technology (ie ALSA vs JACK) than another, then things could run better on one vs the other. That clears up a lot! So, it comes down to this:

Does "REAPER" run with lower latency and less Xruns when using straight ALSA, or through JACK when tested on the same REAPER project?
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Old 07-23-2018, 11:57 AM   #5
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I think that would need testing and might even differ between systems.

FWIW, I suspect that ALSA might have the edge, as reaper then has exclusive access to device, with JACK there might be other clients and there is some code overhead.
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Old 07-23-2018, 01:41 PM   #6
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Quote:
Originally Posted by Jack Winter View Post
I think that would need testing and might even differ between systems.

FWIW, I suspect that ALSA might have the edge, as reaper then has exclusive access to device, with JACK there might be other clients and there is some code overhead.
It is definitely confirmed that ALSA has the edge with CPU cycles. The developers themselves have confirmed that JACK uses more CPU cycles than ALSA alone. But they strongly affirm that JACK itself causes no latency. So ALSA definitely has the edge in that area. :-)
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