[ecasound] problem or bug with chorder or merging chains

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.

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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Received on Fri Jun 10 20:15:02 2016