[linux-audio-dev] Ecasound question

[Kai Vehmanen]

On Tue, 3 Feb 2004, Fons Adriaensen wrote:

> On Tue, Feb 03, 2004 Kai Vehmanen wrote:
>>          -a:2 -i t2.wav -ea:200 \
>>          -a:5 -i t5.wav -erc:1,5 -ea:200 \
>>          -a:2,5 -f:32,10,44100 -o alsa
> Shouldn't there be a  '-erc:1,2' on the t2.wav chain (it should go to
> ouput 2) ?

Yes, error in my example.

>> The '-ea:200' at the end of chains 2 and 5 helps to keep the volume
>> constant. This is ugly, but unfortunately something I cannot fix at this
> Why is this necessary ? Nothing should be mixed... unless alsa inputs
> 2 and 5 are also mixed in. If this is so, can it be prevented ?

Ecasound has to combine chains 2 and 5. Former has 1 channel of audio, the
latter 5 channels. Now the problem is two-fold: first, Ecasound does not
know that only ch5 of chain 5 has audio and others are in fact silent.
Secondly, Ecasound mixes chains by doing channel-by-channel add+divide. So
without the '-ea:200', volume of channels 1 and 5 in the stream going to
the ALSA device would be halved.

It's ugly, but ensures backwards compability.

>> -a:t2 -i t2.wav -erc:1,2 -f:32,10,44100 -o alsa,hw:0
>> -a:t5 -i t5.wav -erc:1,5 -f:32,10,44100 -o alsa,hw:0
[...]
>> -a:t1 -f:32,14,44100 -i alsa,hw:0 -f:32,1,44100 -o t1.wav
>> -a:t6 -f:32,14,44100 -i alsa,hw:0 -erc:6,1 -f:32,1,44100 -o t6.wav
> I kind of like this 'per chain' way of writing things. 

Unfortunately the above examples are not quite correct as '-a:t2 -o
alsa,hw:0 -a:t5 -o alsa,hw:0' is not equivalent to '-a:t2,t5 -o
alsa,hw:0'. The former creates two devices (which will fail in this case
as you can open an ALSA hw-device just once), while the latter creates one
ALSA device and connects it to two chains).

For this reason, I like to write Ecasound setups with one input/output per 
line. This helps to write valid setups.

> Would adding '-erc:1,1' to the a:t1 chain hurt in any way ? It would be
> nice to have a uniform syntax.

It wouldn't change the processing result in anyway, so it's ok. But it 
does add to CPU usage.

-- 
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