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

[Jeremy Jongepier]

On 06/17/2010 10:11 AM, Philipp Überbacher wrote:
> 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

jack_oscrolloscope: http://das.nasophon.de/jack_oscrolloscope/
Sonogram: http://www.christoph-lauer.de/Homepage/Sonogram.html
MeterBridge has an oscilloscope plugin too
And then there's jack.scope, but that one chokes on my computer

Maybe the above links provide some useful info.

Best,

Jeremy