[LAU] Help with jack-volume please

[Len Ovens]

On Wed, 17 Feb 2021, drew Roberts wrote:

> I am not 100% sure I understand it all correctly, but here is what I am
> working on in my effort to help:
> 
> "I have program Audio that will be coming in as AES to the input of the
> Audio Science card (ASI6644)"

AES3 I presume. So stereo program.

> This comes into the machine with the ASI card and gets sent back out to a
> speaker as analog audio. It is intended to play without stopping.

OK

> At 10 minutes past every hour, it should be faded down and specific files
> played out to the same speaker.

The ASI6644 Has Linux alsa drivers, why not use amixer to change the level 
of the program audio going into the card (and out if needed).

> I initially thought of liquidsoap. I get so far and then my skills fail me.
> It seems it should be easy but it is stumping me. I have one more thought to
> perhaps annotate things somehow or whatever.

Unless you actually need a streaming capability to extend across a network 
(you say aes3 in and audio out so no)

> So, I now have a jack graph.

Basically you are using jackd to mix the two signals then which is ok. I 
am not sure what other options are available and jack is probably easiest 
to do. I am not that familiar with the ASI6644 (or any audio science card) 
as they are out of my price range :) but I think it may be possible to mix 
two sets of playback channels in the card itself as it seems to have a 
matrix mixer on the card. This would eliminate the use of jack all 
together. I do not know if the ALSA driver has all the control showing in 
ALSA or if a more direct control is needed. The card does have an API to 
allow custom control applications to be set up.

You also mentioned something about a R-pi... My first question for that 
would be, does the R-pi have a PCIe slot? I know that some SOC cards do 
but my old R-pi 2 most certainly does not :)  However, if you are testing 
on a R-pi then I would assume you have a USB device... many of these do 
not have mixer controls available to ALSA, using real knobs instead. The 
very cheap USB dongles with mic in and headphone out do have ALSA mixer 
controls and might be better for testing.


--
Len Ovens
www.ovenwerks.net