Audio latency

bsduck

Hello,
The default audio latency on NetBSD is huge and I cannot find out how to set it.
I read here about sysctls for this like hw.driverN.latency but I don't have anything like that on my system (NetBSD 9.0 amd64).
The only audio sysctls I could find are

hw.audio0.blk_ms = 4
hw.audio0.multiuser = 0

I also learned about audioctl but I cannot change the values there.
For example if I run audioctl -w play.precision=7 I get play.precision: -> 8
Is there something I have not understood or is my audio hardware just poorly supported on NetBSD?

bsduck

I read this: https://netbsd.org/gallery/presentations/nia/netbsd-audio/
If I understood correctly, the audio system has been deeply reworked for NetBSD 9.0 so I think it's normal the documentation for 8.0 does not apply anymore. However I'm surprised by the default latency using fluidsynth, much bigger than on FreeBSD. May this be because of the OSS compatibility layer? The synthesizer's (fluidsynth from pkgin) only backend option is OSS. I may try compiling it from source and enable the jack backend. Has anyone here ever tried using jack on NetBSD? Or maybe sndio?

bsduck @nia is the person to answer this...

nia

blk_ms is the new latency sysctl, with 4ms being the default depending on your architecture. How are you measuring the latency?

audioctl is only useful if you're doing direct I/O on /dev/sound which is sticky. precision is the bits/sample and not related to latency.

fluidsynth can be compiled from pkgsrc with a range of backends, with OSS being the only one enabled by default. sdl2 is the only one that's interesting to me because it uses the native audio API, and I wrote the code. JACK has no realtime support on NetBSD, fwiw. I haven't looked at what fluidsynth is doing with OSS...

bsduck

Thank you for this answer.

I don't measure latency, I just hear a huge one (something like ½ second) when playing with a midi keyboard connected to fluidsynth. I tried to set blk_ms to a lower value but could not get an acceptable result.

I may try again later but for now I'm giving up with NetBSD. Too many things are not working and/or a pain to configure while it just works with FreeBSD.

In fact I'm experimenting these days with various OS to find the best one for my audio usecases. As of now the best results I could get were with FreeBSD. Linux is usable but still less performant, even using a RT kernel. OpenBSD is useless to me since it has no realtime capability. I still have to try DragonFly but that beast seems not to like my computers and refuses to boot on them...

bsduck

I'm back at testing!

I succesfully built fluidsynth with sdl2 backend. Latency is much better than with the OSS backend, but still not satisfactory compared to what I get with JACK on FreeBSD and Linux.

I used the following configuration:
fluidsynth -a sdl2 -r 96000 -o audio.period-size=64 -o audio.periods=2 -o audio.realtime-prio=99 -m oss -o midi.realtime-prio=0 -o midi.oss.device=/dev/rmidi1

If I set midi.realtime-prio to anything else than 0, I get the following message:
fluidsynth: warning: Failed to set thread to high priority
Maybe the remaining latency comes from the MIDI side. Is there a way to enable realtime priority for MIDI?

I also tried using JACK, but I failed to get any sound.
It outputs sun_driver: running null cycle ... don't know if that's relevant.
Does JACK work for you? If yes I'd be interested in the settings you use.

bsduck

A few more observations:

The NetBSD Guide states that Digital Audio Workstations and other software with support for NetBSD MIDI in the Packages Collection include audio/lmms and audio/fluidsynth. While I can confirm for fluidsynth, I can't for LMMS. I did set the correct input device (/dev/rmidi1) in its settings but LMMS doesn't seem to see any kind of input from my MIDI keyboard. Am I missing something? Does it work for you?
Similar to LMMS, I can't find a way to connect my keyboard to ZynAddSubFX. Since this software doesn't offer any way to set the MIDI input device to be used, I disabled the PC speaker (instructions found here) so that my keyboard became /dev/rmidi0. Still no input.
However, ZynAddSubFX comes with a virtual keyboard which can be played from the mouse or the regular computer keyboard, which is enough for a little testing. Interestingly, although using the OSS backend, latency is low! I noticed you are the one who created the port @nia, did you find out some black magic tricks to reduce latency of OSS emulation? 🙂
The same does not apply when using the built-in ZynAddSubFX (as well as other built-in synths) inside LMMS: latency is high there, although the lowest possible buffer size is selected.
I also tried amsynth, which uses the OSS backend too. Results there were similar to fluidsynth using OSS backend: the MIDI keyboard works, but latency is high (both when playing from the keyboard and when playing a note with the mouse).