[LAU] Can netjack1/2 over a direct ethernet connection substitute for local ALSA audio?

Len Ovens len at ovenwerks.net
Thu Mar 28 16:45:46 CET 2019

On Thu, 28 Mar 2019, crocket wrote:

> On Thu, Mar 28, 2019 at 4:06 PM Len <len at ovenwerks.net> wrote:
>       Jack can not use two devices. speakers (via some kind of on board
>       audio
>       device I assume) and the usb mic will not be in sync and so clicks
>       and
>       pops would be assured. Some kind of sample rate conversion would be
>       needed. zita-ajbridge or alsa-in would work for that.
> Can I not just run two jack servers on Raspberry Pi?

How would that help you? As soon as you want to use the mic and your 
speakers with the same application you will have under and over runs 
between one and the other. The only way around that is to use SRC which 
can be provided by either zita-ajbridge or alsa-in/out (the second comes 
with jack, but the first is better and may now be a part of jackd1). Do 
note that using netjack with the device on the Pi means that the internal 
audio on your desktop can't be used at the same time for the same reason. 
The backend for the jack server on your desktop is the jack server on the 
Pi so any audio device on your desktop would also have to be added via an 
SRC client such as zita-ajbridge or alsa_in/out. This means you desktop 
relies on your Pi for a solid sync... if you are usng your desktop audio 
for anything important that requires solid sync, I would use the local 
device as backend and use zita-njbridge to join the two jack servers on 
the two machines.

> My Gentoo Linux desktop doesn't have pulseaudio. It only has ALSA at this moment.
> I do not want pulseaudio.

No problem (no skype either, but you may not need it) Lots of people use a 
jack to alsa bridge

> I want the voices to not lag too much behind the lips.
> I just want Raspberry Pi and my desktop to share my speakers. Raspberry Pi will
> serve as a morning alarm, and I need to watch videos on my desktop computer.
> I use a USB microphone for foreign language practice and audio calls.

That is what pulse (and the up and coming... maybe, Pipewire) is made for, 
but lots of people do not want to use it, Jack with alsa will get you 
there too. Latency shouldn't be a problem for that use, even with jack 
running 1024/2, though 128/2 should still be stable abd much better.

> I can technically buy a USB hub that supports per-port power switching to have my
> USB microphone turned off most of the time.
> But, since Raspberry Pi 3 B+ supports per-port power switching, I wanted to know
> whether I could use Raspberry Pi as a network USB hub or a network USB
> microphone.

Not sure I know what you mean by that... if any of my guesses are right, 
the answer is I don't know.

Len Ovens

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