Re: channel manipulation

On Sat, September 29, 2012 7:25 pm, Joel Roth wrote:
> On Sat, Sep 29, 2012 at 06:54:11PM +1000, Patrick Shirkey wrote:
>
>> On Sat, September 29, 2012 6:14 pm, Joel Roth wrote:
>> > Hi Patrick,
>> >
>> > You mention the learning curve of Ecasound. I think it
>> > reflects the curve of learning to think in
>> > terms of audio streams and operators for manipulating
>> > them. Similar difficulties dog those who would exercise
>> > the full capabilities of ALSA using .alsarc files.
>> >
>>
>> It's more about the syntax. Being text based it is easy to make mistakes
>> in the signal flow but I am getting my head around it now. It's an
>> elegant
>> way of getting things done once you know what you are doing.
>
> Yes, elegant and yes, with syntactical requirements like
> any programming language.
>
>> The input file is a stereo track. The output file is a 6 channel track.
>
> Oops.
>
>> >> converter script:
>> >>
>> >> ecasound -t 5 -f:s16_be,6,48000 \
>> >> -a:1,2,3,4,5,6 -i TEST_1-2.aif \ # each chain 1-6 gets a copy of six
>> >> channel audio
>> >> -a:1 -chmute:2 \ # chain 1, channel 2 is muted, other 5 channels
>> alive
>> >> -a:2 -chmute:1 \ # chain 2, channel 1 is muted, other 5 channels
>> alive
>> >> -a:3 -chmix:3  \ # chain 3, all six channels mixed to channel 3
>> >> -a:4 -chmix:4  \ # chain 4, all six channels mixed to channel 4
>> >> -a:5 -chmute:1  \# chain 5, channel 1 is muted, other 5 channels
>> alive
>> >> -a:6 -chmute:2 \ # chain 6, channel 2 is muted, other 5 channels
>> alive
>> >> -a:5,6 -o loop,1 \ # chains 5 and 6 summed to loop device loop,1
>> >> -a:7,8 -i loop,1 \ # chains 7 and 8 each get copy of loop,1 stream
>> >> -a:7  -ea:200 -chmix:5 \ # chain 7, all channels amplified, then
>> >                            # summed in channel 5
>> >> -a:8  -chmix:6 \         # chain 8, all channels summed in channel 6
>> >> -a:all -o test-out.wav   # all channels in all chains summed to
>> >> test-out.wav
>> >
>> >
>> > I think this may not be what you want to accomplish, because
>> > you're summing lots of copies of the same channels.
>> >
>>
>> The input track is a stereo track so I am only summing copies of the
>> left
>> and right signal input signal.  The output track is a 6 channel track. I
>> have removed all the additional processing filters to minimise confusion
>> ;-)
>
> Okay, well the comments above still apply, even if the input
> is just two channels. :-)
>

Yep. So should that result in silence on channels 5,6 ?

>
>> >> +++
>> >>
>> >> ecasound: ERROR: [ECA-SESSION] : "Invalid argument, unable to parse:
>> >> "-chmix:5""
>> >>
>> >> ecasound -t 5 -f:s16_be,6,48000 \
>> >> -a:1,2,3,4,5,6 -i TEST_1-2.aif \
>> >> -a:1 -chmute:2 \
>> >> -a:2 -chmute:1 \
>> >> -a:3 -chmix:3  \
>> >> -a:4 -chmix:4  \
>> >> -a:5 -chmute:1  \
>> >> -a:6 -chmute:2 \
>> >> -a:5,6 -chmix:5 -chcopy:5,6 \
>> >> -a:all -o test-out.wav
>> >>
>> >> +++
>> >
>> > Not sure what differently you want to accomplish
>> > with this second command.
>>
>> With the first command I get silence on channels 5,6 output. With the
>> second command I am trying to chmix a:5,6 to channel 5 to see if that
>> gives me an audible signal on the output track. However it fails for
>> some
>> reason. It doesn't want to chmix chain 5 and 6 at the same time. It is
>> happy to do them individually for chain 3 and 4. I'm not sure why that
>> would be a problem though.
>
> I would try creating your setup in small pieces and testing
> each piece. If you can get a good result processing
> chains separately, I would go for that.
>

Ok, With the multi pass approach I have to do the following:

1: Create a four channel track with the correct filters
2: Create a mono track with the left signal inverted
3: Create a new mono track with the track from step 2 summed with the
right channel from the original file
4: Apply my filters on the mono track from step 3 and output a stereo track
5; Combine the 4 channel track from step 1 with the stereo track from step
4 and write a new 6 channel track

That by itself is not a problem but it will add a lot more time to my
processing task I have over 30 hours of audio to process, so I would
prefer to use a single pass solution if possible. Anyway for now I will
program the steps above and if someone has an idea on why the single pass
chain does not work then I will be happy to modify it.

> You may also find it easier (as I do) to write your commands to a file
> (e.g. Setup.ecs) and load it with
>
> ecasound -c -s Setup.ecs
>

I already have a bash script so I'm running it like this:

sh convert.sh


> That way it's more like writing and testing any other program.
>
> Have fun (and working chain setups)
>
> Joel
>


--
Patrick Shirkey
Boost Hardware Ltd

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