Re: Channels and frames
Re: Channels and frames
- Subject: Re: Channels and frames
- From: William Stewart <email@hidden>
- Date: Thu, 3 Nov 2005 11:34:15 -0800
On 03/11/2005, at 11:13 AM, john smith wrote:
William,
thanks for the reply, but I think there's been some
misunderstanding. If I understand you correctly, then you're
talking about the first bus here, something I now know how to
configure.
My question is regarding a second bus (for side-chain). How do I
configure the channel count for that?
No, this isn't limited to the first bus - this goes across all the
buses.
An AU doesn't configure buses, the host does. An AU publishes what
channel capabilities it can deal with, it is expected to deal with
them across all buses it publishes, and the host uses that
information to configure the AU.
Have a look at how this is presented in AU Lab - the AUMerger is
perhaps a good example - its in the Sidechains section of the pop=up
menu for an insert effect.
1 input channel, and 1 output channel). You cannot have mixed
channel counts on input or output buses.
Do you mean to say that if the channel count is, say, 2,2 for the
first bus, then it will always be the same for the second bus?
If so, what happens to the output channel(s) of the second bus?
Should I zero it, or copy from the input?
You have to ensure of course that when the AU is initially opened,
that the configuration you provide is compatible. You can do this in
your constructor after calling CreateElements(), you get the element
for each input and output and set the number of channels appropriately.
After that, the host does everything. The AU should just validate
that the channel configuration provided to it at Initialisation is
legal according to what it published.
The approach we take to this is that if the AU is going to deal
with uneven channel counts (mono input and stereo output), then
it has to be prepared to deal with the full ramifications of that
feature.
I'm sorry, I don't understand. What ramifications? Do you mean to
say that 1,2 is not supported?
No, it means that if you say you can do { 1, 2 } as well as { 2, 2 },
there is no limitations on which input buses can be mono, which
stereo, provided that (in this case) all of the output buses are
stereo. That is what this means, if you have stereo outputs, *any*
input can be mono or stereo.
Bill
Thanks,
Michael Olsen
Here are your choices:
* { {2, 2} {1, 1} }
What this means is that regardless of your number of buses, the
AU can be configured to have 2 input channels and 2 output
channels (or 1 input channel, and 1 output channel). You cannot
have mixed channel counts on input or output buses.
* { {2, 2} {1, 1}, {1, 2} }
That is, you want to allow mono or stereo inputs and stereo
outputs, and for a mono output only mono inputs are legal.
(And for completeness)
* { {2, 2} {1, 1}, {2, 1} }
That is, you want to allow mono or stereo inputs and mono output,
and for a stereo output only stereo inputs are legal.
* { {2, 2} {1, 1}, {2, 1}, {1, 2}}
Any combination of mono or stereo inputs or outputs are allowed.
The approach we take to this is that if the AU is going to deal
with uneven channel counts (mono input and stereo output), then
it has to be prepared to deal with the full ramifications of that
feature. We've looked at ways to somehow publish more restricted
lists, but don't like the complexities this involves.
You can use AU Lab => /Developer/Applications/Audio to test this -
is has support for input and output side chains. CAAudioUnit (in
PublicUtility in the SDK) has code to validate channel
configurations if you want to look at how the host deals with
these. auval will correctly validate these configs.
Bill
On 03/11/2005, at 7:36 AM, john smith wrote:
Hi,
Please disregard my previous question about the output bus. I
think I understand it now.
But... (and someones gonna kill me for asking.)...
an additional "sidechain" input for AU effects is described as
a separate bus - so in your case the AU must specify that it
can handle mono and stereo inputs and outputs (config list:
[1,1], [2,2]) and it must provide two input busses and one
output bus.
How can I inform the host about the channel count on the second bus?
And how can I make sure that it only connect with 1 channel on
the second bus when running in mono mode, and with 2 channels on
the second bus when running in stereo mode?
(i.e. avoid mono sidechains when running in stereo and vice versa).
Thanks,
Michael Olsen
Best,
Stefan
Am 03.11.2005 um 12:35 schrieb john smith:
I'm about to create a channel strip product for a client.
Besides the "usual" channel configurations (1->1, 1->2, 2->2)
it has some alternative configurations, namely 2->1 and 4->2.
The thing about those configurations is that they have extra
side- chain inputs.
For instance, the one I call 2-> has 1 audio in, 1 side-chain
in (which is of course also audio, but I'm sure you're
catching my drift), and 1 audio out.
My question is: If I tell the host (Logic or otherwise) that I
can accept 2 channels in and 1 channel out, will the host know
what the second input is a side-chain input?
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