26 Mar
2019
26 Mar
'19
3:51 p.m.
On Tue, March 26, 2019 23:25, Thomas Brand wrote:
On Tue, March 26, 2019 23:02, Robin Gareus wrote:
Scaling a jack connection is cutting the connection, adding a scaler, then
do two new connections. It can be looked at as expensive, then again if
such a feature is needed for many channels, then a mixer is a good match
to do it as a client.
Going from cut connection, add client, re-connect (basically a
man-in-the-middle scenario): a new example client could make this task
simple, for a specific kind of jack client (1 audio in, 1 audio out).
Something along
jack_connect_mim porta portb mim_client
Say mim can be amplifier (not limited to), for one single line of audio.
It is a regular client and a tool would just help to put it in place in
the graph. Thinking further, it should be possible to remove such
man-in-the-middle again and re-create the original connection. Maybe tool
can be smart and only consider mim clients that indicate via metadata to
be useful for it. These are all not yet fully baked out ideas.
On 3/26/19 11:33 PM, John Rigg wrote:
I had doubts about *when* port gain would be applied, and what you say
Robin makes it clear, basically all of how client ports are ordered for
processing one cycle could potentially be affected, and the smart aspects
therein would be in question.
If ports would have that feature, the next desire would be to automate
it, and it's easy to imagine more DSP that JACK could do, and then we'd
move more and more client work into the server. Instead scaling the signal
(or
any other DSP) should clearly be something that only non-servers should
perform IMO, that are clients (normal or internal).
For a simple mixer: loading an example FAUST script and render a jack
client (without ever touching a compiler, online) isn't too hard either :)
Another note, we can imagine that a metadata property flags a port with a
coefficient, and then client can scale it (as a first or last DSP step)
accordingly. Any thoughts?
On Tue, Mar 26, 2019 at 10:12:32PM +0100, Kjetil
Matheussen wrote:
and disable it by default and add excessive warnings to not enabled it
:)
When this is implemented there are no zero-copy shared buffers anymore.
Port buffers have to pass through a gain-stage first.
Also, direct client-to-client wakeup will not be possible anymore. A
client first has to call some gain-stage or return execution to jackd to
apply the gain. This adds an extra context switch.
Last but not least, gain-changes should be gradual, free of zipper
noise, so there's more complexity.
One of JACK's main concepts was that it provides a mechanism (not
policy). That's also why ports don't include delaylines to compensate
for latency. JACK is supposed to just pass data around and make
information available, not process data.
That being said, you can probably achieve what you want using an
internal-client that implements a gain-stage. Then insert that in
strategic places. Perhaps use the meta-data API to configure it, that
would also get around the issue with port-ownership to control it.
On Tue, Mar 26, 2019 at 10:01 PM Fons Adriaensen
<fons(a)linuxaudio.org> wrote:
>
> The VERY LAST thing I'd want in such a system is a gain control
> on each Jack connection. One very big advantage of digital
> connections, be they MADI, ADAT, Jack, or Dante, is that signal
> levels at all inputs and outputs are exactly defined and can't
> change. Setting up a a similar system using analog connections
> with variable gains would be a real nightmare.
>
Sure, I'm just saying that extending jack with a volume control for
each connection would be a good thing, for those who need it,
which I guess would be the most of us. You are of course free not to
use it if you don't need it.
If anyone does this please make turning it off a compile option.
I can see it causing big problems in a complex setup.