Re: [ecasound] problem or bug with chorder or merging chains

Hi Charles,

Great to see another application for ecasound!

Charlie Laub wrote:
> As part of a real time chainsetup I am using chorder to interleave two
> channels from an existing stream into two of four channels. This is done
> with each of two separate chains, which then must be combined again into a
> single four channels stream so that it can be processed with a LADSPA
> plugin, after which is it sent on to real time outputs. An example of
> ecasound commands for this is shown below:
>
> ecasound -d -z:mixmode,sum \
>
> -a:pre -i:HeCanOnlyHoldHer.flac -f:16,2,44100 -pf:pre.ecp -o:loop,1 \
>
> -a:woofer,tweeter -i:loop,1 \
>
> -a:woofer -pf:woofer.ecp -chorder:1,0,2,0 \
>
> -a:tweeter -pf:tweeter.ecp -chorder:0,1,0,2 \
>
> -a:woofer,tweeter -o:loop,2 \
>
> -a:delay -i:loop,2 -el:mTAP,0,0.006,0,0.006 -o:loop,3 \
>
> -a:DAC1,DAC2 -i:loop,3 \
>
> -a:DAC1 -chorder:1,3 -f:16,2,44100 -o:alsahw,2,0 \
>
> -a:DAC2 -chorder:2,4 -f:16,2,44100 -o:alsahw,3,0
>
>
>
> The problem is that channels 3 and 4 of the stream have no output - they
> seem to be muted or absent.

I think the problem is that the initial -f:16,2,44100
propagates through the rest of the chain setup, limiting
the number of channels exposed to two.

>From the man page, the -f option, "sets the audio stream parameters for
subsequent audio objects".

Loop objects are audio objects, so there should be -f:16,4,44100
in the setup before a four-channel signal goes to a loop object.

I'm not exactly sure where it should go, but it might be
worth amending this line:

> -a:woofer,tweeter -o:loop,2 \

to

-a:woofer,tweeter -f:16,4,44100 -o:loop,2 \

Or more conservatively, changing

> -a:woofer,tweeter -i:loop,1 \

to

-a:woofer,tweeter -f:16,4,44100 -i:loop,1 \
 
Hope this helps!

~Joel
 
> To troubleshoot I did a number of permutations using various LADSPA plugins,
> removing the -el: plugin calls, switching channels between DAC1 and DAC2,
> etc. All signs point to a problem in which the line:
>
> -a:woofer,tweeter -o:loop,2 \
>
> Is not properly merging the chains (summing the channels), or the lines:
>
> -a:woofer -pf:woofer.ecp -chorder:1,0,2,0 \
>
> -a:tweeter -pf:tweeter.ecp -chorder:0,1,0,2 \
>
> are not creating four channels streams that can then be summed together into
> a single 4-channel stream.
>
>
>
> Background and Motivation:
>
> The above chainsetup is implementing a stereo crossover for a 2-way
> loudspeaker and is used for realtime processing and playing of files (as
> shown above). Background on this type of approach can be found here:
>
> http://rtaylor.sites.tru.ca/2013/06/25/digital-crossovereq-with-open-source-
> software-howto/
>
> I have created some LADSPA plugins for filtering (ACDf) and fractional delay
> (mTAP). The mTAP plugin requires that all channels are sent through ONE
> instance of the plugin and not the usual separate instance of a monophonic
> plugin per channel. mTAP has eight channels built into it, so the idea is to
> merge all the channels in the chainsetup (after processing using high and
> low pass filters) into an N-channel stream that is then run through mTAP and
> the appropriate amount of delay is applied to each channel. Because the user
> may have multiple stereo DACs connected to the system, the N-channel stream
> is typically split up into N/2 2-channel substreams, which are sent out to
> N/2 DACs. In the above example there are four total channels (stereo input,
> woofer and tweeter chains). In another common implementation there is only
> one input channel but this might be split into 2,3,4 or more streams for a
> monophonic 2-, 3-, 4- or more way crossover. In either case, there must be
> merging of chains their channels into a single stream for mTAP to process
> and then pairs of channels from this gathered stream are sent to output
> devices (e.g. DACs) in realtime.
>
>
>
> I am not sure if I am not implementing -chorder correctly or if there is a
> bug in its implementation. Perhaps I am not understand how to correctly
> combine channels from multiple chains and that is the cause of the problem.
> I have confirmed that the LADSPA plugins are working correctly. The same
> behavior occurs even if no LADSPA plugins are used.
>
>
>
> Any help or advice is appreciated.
>
>
>
> -Charlie
>
>
>

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-- 
Joel Roth
  
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