Re: [ecasound] Mixing operator

From: Joel Roth <joelz@email-addr-hidden>
Date: Fri Mar 20 2009 - 04:30:24 EET

On Thu, Mar 19, 2009 at 09:28:57PM +0000, Krzysztof Foltman wrote:
> [...]what about a
> better way to route channels in multichannel stream?
> Something like -chselect:0,5,3,4 (produces a 4-channel stream that
> routes incoming channel 0 to outgoing channel 0, incoming channel 5 to
> outgoing channel 1, incoming channel 3 to outgoing channel 2 etc) - the
> input channels that are not specified would be ignored.
> This is probably hard to implement as it has a different number of input
> and output channels, but the only alternative I see (that is generic
> enough to allow, say, swapping left and right channels) involves a lot
> of -chmove and possibly more than just one chain (which, as far as I
> know, introduces latency).

Parallel chains do not increase latency, as far as I know,
beyond the amount related to the size of the buffer between
the inputs and outputs.

Chains joined sequentially via loop devices do pay a price in
higher latency, a fixed amount for each loop device.

> Can be really useful for processing multichannel files and/or working
> with a multichannel soundcard. I was trying to write my own "dumb
> recorder" style PyGTK frontend, but doing routing in a way that would
> allow recording from input 2 on track 1 (plus analogical setup for
> monitoring at the same time) without loops and extra latency, looked
> hard enough to put the project on the backburner.

If your soundcard has hardware monitoring, that offers one
way to monitor at low latency while recording. JACK
probably also provides suitable mechanisms for routing
and monitoring with low latency.

If so, you could then use Ecasound (or Ardour or any JACK
capable recorder) to capture the audio to disk.

Nama, my attempt at an Ecasound front-end, currently
introduces a loop device whenever two outputs (i.e. file and
soundcard) are asking for the same signal.

Nama can route any soundcard input to any soundcard output,
however the latency would rise (due to loop devices) if you
were recording those signals at the same time.

I believe that the mixer and mixdown functions could be serviceable
for wider signal formats. (A couple minor tweaks might be
Nama currently has compensation for latency differences
between tracks introduced by LADSPA effects. Latency
measurement and adjustment for tracks recorded against a
prerecorded accompaniment is still a TODO item.



> Krzysztof

Joel Roth
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Received on Fri Mar 20 08:15:01 2009

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