[PD] request assistance with crackles and pops in VFOs driven by modulating accelerometer signals

Andy Farnell padawan12 at obiwannabe.co.uk
Thu Jul 24 00:06:54 CEST 2008

The combination of problems and tests does seem strange.

In a case like this a good debug approach may be to log 
everything from the controller to a file and look through
it for strange jumps.

A [lop~ 10] following the [sig~] might help smooth the data
better than a [line~]

On Thu, 24 Jul 2008 00:17:32 +1000
Darren Kelly <darren at webel.com.au> wrote:

> Hi PD,
> I am getting crackles when driving the frequency of an osc~ with an 
> accelerometer signal
> (in fact I'm driving 3 x 2 = 6 oscillators with Wiimotes as wireless 2 
> triaxial accelerometers) ,
> which one can hear in the following mp4 movie (at the end when I am 
> waving the sensors faster):
> http://www.webel.com.au/project/drancing/wii/movie/iSight.320x240/Drancing_PD_Wii_iSight.VFO.1.320x240.mp4
> The Pure Data patch for one channel can be seen here:
>     http://www.webel.com.au/project/drancing/puredata/VFO.pd.png
> And the whole system's patches can be seen here:
> http://www.webel.com.au/project/drancing/puredata/index.jsp?page=DranceWarePureDataWii
> Each conditioned accelerometer channel can drive a Variable Frequency 
> Oscillator (VFO) (osc~) with the option
> of locking onto discrete MIDI note frequencies, as well as a frequency 
> scaling, a frequency offset, and an output gain.
> I have tried inserting a sig~ before the osc~, it made no audible 
> difference.
> I have tried including a line and line~ to smooth the signal before 
> varying the frequency, it made no audible difference.
> I now have a limiter~ in COMPRESS mode at the output, did not help
> (it certainly helped with many other things, just not with my VFO problem).
> The amplitude definitely remains constant during this.
> When I open up the osc~ examples and pump the frequency very quickly 
> with just
> a mouse over the feeding number as simulated driver I don't get any 
> problems at all.
> Note however that I am driving 6 oscillators (and a lot more stuff) when 
> running my full system,
> however I'm not topping out my CPU, so I don't think that's the problem 
> either.
> Am bamboozled, since I don't recall having this trouble using the same 
> naive strategy
> with an equivalent JSyn audio synthesis system.
> Very glad for any suggestions and help,
> Darren
> -- 
> Darren Kelly, BSc, PhD
> phone: +61 (2) 9386 0090
> post: PO Box 1816, Bondi Junction, NSW 1355, Australia
> http://www.webel.com.au 
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Use the source

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