Re: [SoX-devel] effect to write waveforms to image file

[Thor A. <ta...@to...>]

On Tue, May 29, 2012 at 01:27:57PM +0200, armin walland wrote:
> On Thursday 24.05 11:53:24 Thor Andreassen wrote:
> > I've attached an updated version of the aplot script. With the -P
> > switch it outputs a 1280x1024 png image to stdout.
> 
> the script seems to die on me at line 42 at . $ZSHLIB/utils. looks
> like i am missing some libraries for zsh, since $ZSHLIB is empty here
> and i have no 'utils' directory in my zsh package (arch linux).

Ouch my bad, utils is library file I wrote, you only need it for the -C
option to generate hyphenated and comma separated lists, so if -C is not
used line 40 and 42 can be commented out.  I've attached the utils file
if you decide to use it. ~/etc/libfunctions just exports the ZSHLIB
variable.

[...]

> anyway, i tried using sox & gnuplot in binary mode, but it is still
> too slow,
> 
> i also tried using sox's downsample effect, but that didn't seem to
> make much of a difference:

Yes this is decidedly a workaround and there are more efficient and
useful ways of accomplishing this. The thing is, the data should be
compressed somehow without loosing too much information ie. local minima
and maxima, and the compression should take into account the number of
pixels that the user has available, so maybe something like this:

input  : S = [buffer of samples]
output : maxmin(S)

Where the buffers size is = samples / horizontal-pixels, and where
maxmin might be plotted in the same column. AFAICS a sox effect is a
pretty good and useful place for such a solution, as you proposed.

[...]

-- 
best regards
Thor Andreassen