[Jack-Devel] Does alsa_in reading from SPDIF input inject pops and clicks?

crocket crockabiscuit at gmail.com
Sat Aug 10 00:44:51 CEST 2019

I'm trying to share speakers with my desktop computer and Raspberry Pi 3
B+. Both machines should be able to play audio simultaneously.

--> is a connection that doesn't cross the boundary of a computer.
==> is a connection that occurs between two computers.

Anything that doesn't cross ==> occurs on my desktop computer. Anything
that happens after ==> occurs on Raspberry Pi 3 B+.
netjack1 runs on my desktop computer. Ethernet cable is the only cable that
connects two machines.

1. ALSA dmix --> SPDIF out of Realtek ALC887 onboard soundcard --> SPDIF In
of X-Fi HD USB --(alsa_in or zita-a2j)--> netjack1 ==(ethernet cable)==>
ALSA jack backend --> I2S Amplifier(HiFiBerry Amp2) --> Speakers
2. netjack1 --(alsa_out or zita-j2a)--> headphone jack of X-Fi HD USB on my
desktop computer --> headphones

netjack1 can route audio to either headphones or HiFiBerry Amp2. I can
control routing via a keyboard shortcut.
netjack1 can accept audio from alsa_in, zita-a2j, or just regular JACK
clients like mpv.

Here are questions.

1. If SPDIF out of Realtek ALC887 onboard soundcard stops emitting clock
signals, would the following audio route cause pops and clicks in alsa_out
or zita-j2a?
mpv --> netjack1 --(alsa_out or zita-j2a)--> headhpone jack of X-Fi HD USB
--> headphones
I suspect that if SPDIF out doesn't emit clock signals and the clock source
for X-Fi HD is SPDIF, alsa_out can misbehave. If SPDIF out may not emit
clock signals in the absence of audio signals, everything should be routed
via SPDIF out.
2. If SPDIF out stops emitting clock signals in the absence of audio
signals and starts emitting them again in the presence of audio signals,
can alsa_in or alsa_out be confused and inject pops and clicks into audio?

On Fri, Aug 9, 2019 at 11:08 PM Chris Caudle <chris at chriscaudle.org> wrote:

> On Thu, August 8, 2019 10:31 pm, crocket wrote:
> > If SPDIF Out stops emitting clock signals in the absence of audio
> signals,
> > would alsa_out working on the headphone jack of the USB soundcard that
> > gets its clock signals from SPDIF Out emit pops and clicks?
> The USB audio interface is getting clock from the S/PDIF input, but the
> audio is coming from USB, not from the S/PDIF input?
> Can that configuration be set with the controls available for the Sound
> Blaster device you mentioned?
> > 1. ALSA dmix(period size 512, periods 3) --> SPDIF Out of onboard
> > soundcard(Realtek ALC887) --> SPDIF In of Creative Sound Blaster X-Fi HD
> > USB --(alsa_in, period_size 512, periods 3)--> netjack1 ==(ethernet)==>
> > ALSA jack backend --> Amplifier --> Speakers
> > 2. netjack1 --(alsa_out, period_size 512, periods 3)--> headphones
> This description is a little bit confusing regarding where the machine
> separations occur.
> So the onboard sound card is on one computer, the Sound Blaster X-Fi is
> connected to a second computer?  And that second computer drives speakers
> via the X-Fi output, and is also connected via Ethernet to a third
> computer?
> It is not clear where the netjack connection comes in, for the connection
> labeled  with a "2." it shows netjack to alsa-out, but it is not clear
> which physical interface drives the headphones.
> Perhaps a description of the physical connections of which computer is
> connected to which interface would help, along with a description again of
> what you are trying to achieve.   You probably described that before, but
> I think it has been some number of weeks, I'm not sure I could find the
> original email.
> --
> Chris Caudle
> _______________________________________________
> Jack-Devel mailing list
> Jack-Devel at lists.jackaudio.org
> http://lists.jackaudio.org/listinfo.cgi/jack-devel-jackaudio.org
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