Re: [Sndobj-devel] PySndObj: Problem with SndObj & time.sleep() -- making a metronome with SndObj

[Victor L. <Vic...@nu...>]

Instead of turning the thread on and off, you can try using 
SndObj::Disable()/Enable() to
turn the processing of an object off  (outputs zero thereafter)/on. Or you
can use SetAmp(0) on the Oscili object that zeros the amplitude.

Because there are two threads, timing might be slightly wobbly. If you
need precision you can set a callback that calls either method. This will
be called from the processing thread, always before processing. The
timing resolution then is however many samples your vector is (you
can bring it down to 1 sample if you need).

Callbacks for SndThread were introduced in the latest version (better
get the latest CVS) and are documented in the latest reference manual.
There are some examples of its use in the python subdir of the sources.

Victor

At 05:55 29/01/2007, Craig Lewiston wrote:
>One use of SndObj in my application is to provide the audio "beep" for
>a metronome thread that executes alongside my main program loop (a
>Tkinter GUI).  I figured the easiest way to go about this would be to
>stick the following steps inside a loop:
>
>1) turn the sound on,
>2) wait for the beep length (in this case 50 ms),
>3) turn the sound off,
>4) wait the remainder of time until the next beat.
>
>The four steps would reside inside a loop that executed for the
>duration of the song.  However, working towards that end, I've found
>that when i simply attempt to do the following (without putting it in
>a loop):
>
>thread.ProcOn()
>time.sleep(0.05)
>thread.ProcOff()
>time.sleep(0.45)
>
>I don't get the desired effect.  I want the sound on for 50 ms, and
>then off for 450 ms.  Instead, with the above code, I get 50 ms of the
>desired sound (a sine wave in this case), followed by 450 ms of a
>distorted version of the sound.  It seems to be a weird interaction
>between SndThread and time.sleep.
>
>When i do this:
>
>thread.ProcOn()
>time.sleep(0.05)
>thread.ProcOff()
>
>or this:
>
>thread.ProcOn()
>time.sleep(0.05)
>
>I get the desired result: 50 ms of a sine wave.  (In the second case,
>I really don't understand why it stops WITHOUT the thread.ProcOff()
>statement, but that's not the issue here)
>
>if I do this:
>thread.ProcOn()
>
>I get NO output, which is weird because i would expect it to just turn
>the sound on and not turn it off until i hard-closed the Python
>Interpreter.
>
>Here's the full code:
>------------------------------------
>import sndobj
>import time
>
>tab = sndobj.HarmTable(5000,2, 1)
>osc = sndobj.Oscili(tab, 3000, 16000)
>outp = sndobj.SndRTIO(1)
>outp.SetOutput(1, osc)
>
>thread = sndobj.SndThread()
>thread.AddObj(osc)
>thread.AddObj(outp, sndobj.SNDIO_OUT)
>
>thread.ProcOn()
>time.sleep(0.05)
>thread.ProcOff()
>time.sleep(0.45)
>------------------------------------
>and my system specs: OSX 10.4.8, Powerbook G4, Python 2.4.4
>
>
>So, I'm sorta at a loss for what to do.  I've gone through enough
>trouble to get SndObj up and running (I was using tkSnack before
>[http://www.speech.kth.se/snack/]), which gave me problems of its own
>(intermittent playback quality).  I'm trying to figure out if I should
>stick through with SndObj for realtime audio processing in my
>application, or look for another module.
>
>Also, concerning the metronome problem, I was wondering if maybe the
>better route to take, instead of creating a loop to start and stop the
>sound, would be instead to create one metronome audio track that lasts
>the length of the song, and then just play it at the beginning and
>stop it at the end.
>
>Thoughts?
>
>Thanks,
>Craig
>
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Victor Lazzarini
Music Technology Laboratory
Music Department
National University of Ireland, Maynooth