Re: [SoX-users] step backward in file for effects proessing?

[Erich E. <er...@ec...>]

Am 12.07.2015 um 22:20 schrieb forget color:
> I want to reprocess parts of a file after I already did something to it. 
> 
> For example, let's say I have a 5 second file and I want to adjust the
> speed of seconds 0-3 to 1.02 and, after that adjustment, I want to
> adjust the speed of seconds 0-2 to .98. So in trim notation what I'd
> want is something like:
> 
>    play in.wav trim 0 3 speed 1.02 : trim -3 3 speed 0.98
> 
> But I can't use a negative number as the first input to trim.
> 
> I could accomplish it with this:
> 
>   sox in.wav tmp1.wav trim 0 3 speed 1.02
>   sox tmp1.wav out.wav trim 0 3 speed 0.98
> 
> But is there a way to do this in one command? I don't just want it for
> one step back but constantly over an entire file.
> 
> thx
> fg
> 

Hi,

this won't work in one effects chain: Once you've cut it out with trim
for re-speeding, the remaining samples go to another effects chain.
Thus, samples from the first and second part can't be accessed from the
same speed-command.
However, what you can do is to use a second sox-command (as you did),
but without a temporary file:

sox in.wav -p trim 0 3 speed 1.02 : | \
sox -t sox - out.wav trim 0 3 speed 0.98

I assume, your command line is not, what you actually attempt, becaus
1) it doesn't fit your verbal description
2) you _could_ fit it in one line:

sox in.wav out.wav trim 0 3 speed 1.02 speed 0.98

greetings,
Erich