Re: Confusion about Fading Amplification

On Thu, Aug 04, 2011 at 09:30:32PM -0400, Mark Armendariz wrote:
> * Note: I assume attachments are not kosher on this list, so I posted
> this question on StackOverflow as so you can see my resulting
> waveforms:
> http://stackoverflow.com/questions/6950482/how-do-multiple-amplitude-fades-work-on-ecasound
> 
> -----
> 
> I want to fade a track in and out as specific time codes.  For
> example, I would like to take an audio file, and:
> 
> Start it at 100% Volume,
> Fade it to 20%  at 2 seconds
> Fade it to 100% at 4 seconds
> Fade it to 20%  at 6 seconds
> Fade it to 100% at 8 seconds
> Fade it to 20%  at 10 seconds
> Fade it to 100% at 12 seconds
> Fade it to 0 at 14 seconds.


I see you've been using multiple -kl2 and -ea operators.

While that may be possible, you may find it simpler
to create a single envelope using -klg. For the above example (not
tested) you could try this:

ecasound -a:1 -i:tone.wav -ea:100 \
-klg:1,0,100,7,1,2,0.20,4,1,6,0.20,8,1,10,0.20,12,1,14,0 \
-o:test.mp3

The arguments for -klg are:

fx-parameter, low value, high value, count (no. of pairs), 
pos1, value1, pos2, value2,...

The values are specified between 0 and 1.

Hope this helps...

 
> I've been testing this with a constant tone generated by ecasound so
> that I can open the resulting file in Audacity and see the results
> visually.  As far as I can tell, increasing the amplitude is relative,
> while decreasing it is not.  It seems that if I fade the amplitude up
> that it affects the volume of the whole track and not just at the
> specific time I set the fade, which is where I'm getting lost.
> 
> Note: I seem to have figured out the "why" as I was coming up with
> examples, but I'm still hoping you can explain if this is correct or
> if there is a "better" way.
> 
> An example of what has me scratching my head
> -----------------------------
> 
> # generate the tone
> ecasound -i tone,sine,880,20 -o:tone.wav
> 
> # Just the test to see that i can fade start it at 100 and fade it to 20.
> ecasound -a:1 -i tone.wav -ea:100 -kl2:1,100,20,2,1   -a:all -o:test_1.mp3
> 
> # Fade it out and in
> ecasound -a:1 -i tone.wav -ea:100 -kl2:1,100,20,2,1   -ea:100
> -kl2:1,20,100,4,1   -a:all -o:test_2.mp3
> 
> # Fade it out and in with a peak of 500
> ecasound -a:1 -i tone.wav -ea:100 -kl2:1,100,20,2,1   -ea:100
> -kl2:1,20,500,4,1   -a:all -o:test_3.mp3
> 
> # Fade it out from 500, out, and then back to 500
> ecasound -a:1 -i tone.wav -ea:100 -kl2:1,500,20,2,1   -ea:100
> -kl2:1,20,500,4,1   -a:all -o:test_4.mp3
> 
> # Fade it out from 500, out to a low of 10, and then back to 500
> ecasound -a:1 -i tone.wav -ea:100 -kl2:1,500,10,2,1   -ea:100
> -kl2:1,10,500,4,1   -a:all -o:test_5.mp3
> 
> # Fade it out from 1000, out to a low of 10, and then back to 1000
> ecasound -a:1 -i tone.wav -ea:100 -kl2:1,1000,10,2,1 -ea:100
> -kl2:1,10,1000,4,1 -a:all -o:test_6.mp3
> 
> # The eventual result I'm looking for
> ecasound -a:1 -i tone.wav -ea:100 -kl2:1,500,20,2,1 -ea:100
> -kl2:1,20,500,4,1 -ea:100 -kl2:1,500,20,6,1 -ea:100 -kl2:1,20,500,8,1
> -ea:100 -kl2:1,500,20,10,1 -ea:100 -kl2:1,20,500,12,1 -ea:100
> -kl2:1,500,0,14,4 -a:all -o:test_7.mp3

Hi,


 
> -------------------------------
> 
> The best I can tell from these results is that the amplitude of the
> whole track is relative to the difference between the low and the peak
> of all the fading effects.  I'm not sure if this result is expected,
> but it's very confusing.
> 
> Also, in the last result, the fades are no longer taking a full second
> each.  In order to figure out why that may be, I took the final
> fade-to-zero off and the durations were back to normal.  This does not
> seem like expected behavior.
> 
> -------------------------------
> 
> # "Fixing" the fade durations
> ecasound -a:1 -i tone.wav -ea:100 -kl2:1,500,20,2,1 -ea:100
> -kl2:1,20,500,4,1 -ea:100 -kl2:1,500,20,6,1 -ea:100 -kl2:1,20,500,8,1
> -ea:100 -kl2:1,500,20,10,1 -ea:100 -kl2:1,20,500,12,1 -a:all
> -o:test_8.mp3
> 
> -------------------------------
> 
> 
> As a side note, I've also tried changing the -ea values to the
> "current" amplitude with every line. It didn't make any difference (no
> matter what I set -ea to)
> 
> I have the very latest installed from git (2.8.1+dev). I had these
> same issues with 2.7.0, which is why I upgraded and eventually found
> myself here.
> 
> Am I doing this wrong?
> 
> Thank you for your time.
> 
> ------------------------------------------------------------------------------
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-- 
Joel Roth

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