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

Darren Kelly darren at webel.com.au
Wed Jul 23 16:17:32 CEST 2008

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):


The Pure Data patch for one channel can be seen here:


And the whole system's patches can be seen here:


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 

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 

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 Kelly, BSc, PhD
phone: +61 (2) 9386 0090
post: PO Box 1816, Bondi Junction, NSW 1355, Australia

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