Re: [SoX-users] Generating multiple spectrograms

[Ulrich K. <ul...@ch...>]

Peter Shute <ps...@nu...>:

> I'm not seeing such big differences. I get 21 seconds for -y 642,  
> and 15 for -y 1025. It's only 6 for -y 513, but it's still not the  
> 11x difference you're seeing.

Well, that's surprising. But if -y 642 is fast enough for you, by all  
means do use it. :)

> That's a pity. I saw how easy it is to use:
> trim 0 3:00 : newfile : restart
> to split it into 3 minute files and hoped spectrograms could be done  
> in a similar way.

In principle, it can (just put the spectrogram effect after trim and  
before the ":"), but there is no way to specify different output file  
names for each pass. You could try to move each file out of the way  
while the next part is being analyzed (the file won't be overwritten  
before the spectrogram is complete), but that's not very reliable.

As you are on Windows, my idea regarding named pipes won't work  
either. Outputting to stdout might achieve the same, but it is a  
recent addition and not in any released version, thus would require  
recompiling.

So the only way seems to be to resort to shell scripting, some  
equivalent of this bash script:
for i in `seq 1 15`
do
   sox ... trim $((3*i)):00 3:00 ... -o spectrogram$i.png
done
This at least saves you from typing a lot of lines.

>> Probably the easiest way is to lift the width limit of 5000 pixels,  
>> as it appears to be arbitrary. I don't know if there is a real limit
> That's tempting, but every time I get involved in recompiling, it  
> ends up as a series of brick walls till I give up (I'd need a  
> Windows version). 50,000 should do for 30 minutes, but I might need  
> perhaps 4 or 6 times that, assuming png format will allow it.

Seems to be OK. In the meantime, I read that PNG supports up to two  
billion pixels (2^31-1), and tried successfully with 100000 pixels, so  
libpng apparently doesn't mind. (Imagemagick's display crashed with a  
segmentation fault, but I could view the result in GIMP.)

Ulrich