[LAD] Real-time plotting of audio/ oscilloscope.

[Philipp Überbacher]

Excerpts from James Morris's message of 2010-06-17 09:57:26 +0200:
> On 17 June 2010 08:20, Peter Nelson <peter at fuzzle.org> wrote:
> > On Thu, 2010-06-17 at 00:29 -0400, Jeremy wrote:
> >> Hi,
> >>
> >>
> >> When I'm programming, I find it immensely helpful to be able to plot
> >> audio data at different points in its processing, for debugging, and
> >> to test new ideas.
> >>
> >>
> >> Essentially I want an oscilloscope, which plots each chunk of 1024
> >> samples.
> >>
> >>
> >> I've tried using libplot, but it seems too slow.  It's causing
> >> constant xruns, even when I only plot every 5th sample.
> >>
> >>
> >> I thought that maybe libplot was too abstract, and that I needed to
> >> draw the pixels on the screen directly.  I tried using SDL, but it
> >> caused excessive xruns also.  Simply setting 48000 pixels per second
> >> was enough to cause the flow of xruns.  This is  *not* erasing the
> >> screen, just drawing the points.  I'd expect that erasing the screen
> >> is the slow part, but apparently not.
> >>
> >>
> >> At this point I'm not sure if it's even possible to plot the audio
> >> data in realtime.  I did a rough calculation, that on my 2 Ghz cpu, it
> >> should have roughly 40,000 cycles to process each sample.  It seems to
> >> me that considering running the whole plugin only uses 1/4 of my cpu,
> >> the other 30000 cycles should be plenty to put a pixel on the screen.
> >>
> >>
> >> So I would guess that something else is the bottleneck, like my video
> >> chip, or maybe the libraries I'm using.
> >>
> >>
> >> So basically my question is:  Has anyone else had any luck with
> >> plotting audio data in real time, and if so, how?  Is it not possible
> >> to plot every sample, but only a certain percentage of them?  Is there
> >> a fundamental restriction on doing so, or is my problem in software?
> >
> > I'm going to assume you're plotting directly within the realtime process
> > thread, which will never work. Push the audio data in a ring buffer,
> > then do the plotting in your main thread.
> >
> 
> How about taking a look at some of the sound editors, snd, mhwaveedit,
> etc? Or perhaps Freqtweak?
> 
> I seem to recall seeing a reference somewhere recently, to
> oscilloscope type software, which also might be useful to read the
> code of, but can't remember where.
> 
> James

Well, there's ll-scope, but no idea how close it is to what you want:
http://www.student.nada.kth.se/~d00-llu/music_dssi.php?lang=en
-- 
Regards,
Philipp

--
"Wir stehen selbst enttäuscht und sehn betroffen / Den Vorhang zu und alle Fragen offen." Bertolt Brecht, Der gute Mensch von Sezuan