[PlanetCCRMA] Ardour hardware monitoring

[R Parker]

--- John Yates <jyates@hvc.rr.com> wrote:
> Ron,
> 
> Thanks for your reply. I think this is becoming a
> little clearer for
> me. Unfortunately, I don't think I'll be able to do
> what I was
> hoping to do. I'll try to explain. This may or may
> not apply to your
> hardware and I still may not have it quite right,
> but here are my
> present assumptions.
> 
> The RME Digiface, is set up with 26 hardware inputs
> (24 ADAT, 2 SPDIF),
> 26 software playback inputs (these are selected in
> Ardour as if they
> were hardware outputs) and 28 actual hardware
> outputs (24 ADAT,
> 2 SPDIF, and 2 analog/headphone). Each of the 52
> inputs has a level
> (fader) send to each of the 28 outputs. Routing
> (buss connect) changes
> never happen since everything is routed everywhere
> all the time.
> This means that there are 1456 virtual faders that
> control what signals
> appear at what outputs and at what level at any
> given time. Inputs going
> into Ardour bypass the mixer and are not level
> controlled.
> 
> Now for hardware monitor switching to occur during a
> punch in, a
> software playback level would have to go down and a
> hardware input
> level would have to go up. At punch out the levels
> would switch
> back again.

When a track is record armed and a rolling transport
is record engaged, existing routes from disk cease to
playback and the new incoming signal (punch in) is
recorded to the relative track. The logic is that a
disk signal can't playback because it's being
overwritten.

With hardware monitor on, hardware input ports route
the signal to two destinations; the relative user
defined soft input port and its hardware output port.
This enables you to play along with yourself until the
rolling transport is Record engaged--see the first
paragraph.

The question, as it relates to the above example, is
what hardware output port does an input port route to
when hardware Monitor is on. It stands to reason that
this must be dictated by the user defined routes for
any given session. If a stereo master bus is the
playback destination in a multitrack session, then
that bus must also be the playback destination of
hardware monitor enabled inputs.

If my assumptions are accurate, the only levels you
would adjust in the hardware mixer are incoming
gain/trim and the master bus output.

Control Room monitor volume is controled at the master
playback bus in Ardour. However, the hardware mixer
could be treated as an extra playback gain stage. For
practicle purposes, the hardware mixer should be setup
and left alone. You don't want to jump in and out of
two mixers during a session. It isn't necesarry and
it's extra work.

> Here's the rub. Levels to which output channel?
> Remember, each input
> has 28 possible output 'send' levels.

By "levels" you mean destinations or hardware playback
ports. It can be that there are 28 available ports but
the actual routes would be dictated by an Ardour
session.

If alsa_pcm:playback_1,2 are hardware 1 and 2 and they
are the destination of ardour_master-bus:playback_1,2 
then input 9 (guitar) hardware monitor signals will
route to hardware 1 and 2 because it's dictated in the
Ardour user defined routes. Remember, my proposals are
all based on assumptions.

So that's our master control room routes. Now, add an
external effect unit into the mix. This should shed
some light on possible usage for the remaining
hardware ports.

In the Ardour session add a stereo bus with inputs of
alsa_pcm:capture_3,4 and playback
alsa_pcm:playback_1,2 which is the master bus. In any
mixerstrip with two in two out routes add sends to
alsa_pcm:playback_3,4. I don't know the correct Ardour
terminology but what we're doing is creating a typical
stereo bus. Because this bus is an Ardour mixerstrip
you can insert pre and post fader effects;
compression, equalization, etc.

Of course hard disk sources will route through the bus
but Hardware monitor signals won't. The only way to
address this problem is to have very stable lowlatency
and use software monitor rather than hardware monitor.

 My guess, and
> I can't test right
> now because I'm at work, is that it would be the
> sends to whatever
> hardware output channel is selected in Ardour's
> mixer strip.

Exactly. Which is what I've tried to describe.

 This is
> probably great if you are using Ardour with an
> outboard mixer.
> However, what if your tracks are not sending to
> individual hardware
> outputs, but rather to an internal Ardour stereo
> master buss. There
> is no selected hardware output to send the input to
> in this case.

I believe there is and it must be the playback ports
of the Ardour master bus. You should test this.

 Ardour
> defaults the output of the master fader to hardware
> outputs 1 and 2
> which in reality means playback inputs 1 and 2 on
> the hardware mixer.

Exactly.

> The levels of these two inputs going to the
> analog/headphone output are
> what I am using for monitoring.

Is there only one D/A on the hardware? Adding external
convertors would be interesting. 

 Even if Ardour could
> assume that you
> were monitoring via playback inputs 1 and 2, it
> still wouldn't know
> which hardware outputs you were actually listening
> to in order to
> send the hardware input there.

I'm thinking this isn't true because all inputs
eventually route to the 1 and 2. They would be the
default route.

I've got a session coming in and don't have time to go
back and correct my thoughts. I hope they aren't to
confusing. One thing I have to point out is that it's
so much easier to setup working configurations than it
is to describe them in written form. :)

ron

 And even if you told
> it explicitly you
> would not get whatever level was set for the track
> in Ardour's mixer.
> 
> What I believe all this means is that zero latency
> hardware monitor
> switching for punching into tracks is only valid if
> you are using an
> outboard mixer to get your stereo monitor mix. To
> achieve what I was
> thinking about would require the actual mixing to
> take place in the
> hardware mixer with Ardour simply acting as a
> controller and this is
> not the case.
> 
> Sorry, if this was already obvious to everyone. Just
> trying to get a
> handle what's possible with this set up. And please
> correct me if I am
> wrong!
> 
> John
> 
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>
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