Re: [ecasound] problem with .ewf in ecasound 2.0.1

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Subject: Re: [ecasound] problem with .ewf in ecasound 2.0.1
From: Kai Vehmanen (k_AT_eca.cx)
Date: Wed Sep 26 2001 - 00:27:37 EEST

On Tue, 25 Sep 2001, Julien Patrick Claassen wrote:

> ecasound -a:1 -i 1.ewf -a:2 -i 2.ewf -a:all -o my_long.wav
[...]
> It worked well. The files were put one after the other. But there has
> been a great difference between the volume levels. The later of the files

This is expected behaviour. You can never assign multiple inputs (or
outputs) to one chain in ecasound. So with your ewfs, you have:

1.ewf ******** |
2.ewf ******** |-> my_long.wav
3.ewf ******** |

Now you have arranged the files so that they don't overlap, but ecasound
doesn't know this. So when mixing to my_long, it creates output samples by
calculating (in1 + in2 +in3 / 3). So as a result, my_long.wav is
three-times more quiet than the original files.

But as ecasound internally uses floating-point numbers to represent audio,
you won't lose dynamics of your input signals in the above process.
Dynamics are lost only when converting to fixed-point format (ie. when
writing a 16bit wav-file). So, you can either...

1) amplify before mixdown:

ecasound -a:1 -i 1.ewf -ea:300 \
                -a:2 -i 2.ewf -ea:300 \
                -a:3 -i 3.ewf -ea:300 \
                -a:all -o my_long.wav

2) use floating point intermediate wav-file

# mixdown to float-file
ecasound -a:1 -i 1.ewf -a:2 -i 2.ewf \
        -a:all -f:f32_le,2,44100 -o my_long_floatfile.wav

# then use the -ev normalize to maximize volume
# of the temp file (without losing dynamics)
ecasound -i my_long_floatfile.wav -f:s16_le,2,44100 -o my_long.wav -ev

# or alternatively apply the 300% amplify as the 2nd step
ecasound -i my_long_floatfile.wav -f:s16_le,2,44100 -o my_long.wav -ea:300

3) do it in one step using loop-devices (a bit
   more complicated)

ecasound -a:1 -i 1.ewf \
         -a:2 -i 2.ewf \
         -a:3 -i 3.ewf \
         -a:1,2,3 -o loop,1 \
         -a:4 -i loop,1 -o my_long.wav -ea:300 

-- 
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