[pd] [noise~],[expr~], questions

[Mathieu Bouchard]

On Tue, 12 Dec 2006, hard off wrote:

> sorry, i have a few questions today, i know it's bad from to ask them
> all in one thread, but i don't want to start too many threads.
> question 1)
> how do you multiply a signal by a power of n ?  can you do it with expr~?

you might mean "raise a signal to the nth power". the way you wrote it is 
somewhat confusing (but still guessable). [expr~ pow($v1,$f2)]

> is there a list of the functions that i can use with expr~ (and expr) ? 
> i have seen many of these functions in other peoples patches, but can't 
> find them in pd's documentation.

[expr~] is considered an external, that is just bundled with pd. Beyond 
the help file, your best bet might be looking at vexp_fun.c. It might be C 
code, but at least you can find the names of all the allowed functions.

> i want to insert a percentage of random noise into a signal.  ie, for 
> every oscillation of an [osc~] i want 25% of the samples to be converted 
> into noise.  the level and position of the noise should be random, but 
> 25% of the samples in each oscillation must be be converted into noise. 
> any idea how to do that?

25% of samples might sound a lot noisier than what you want. Perceptually 
you will not have something damaged by only 25% and you'll be lucky if you 
still hear something. It's not as if you replaced 25% of pixels by noise 
in an image.

If you still want to do it, you can do it like:

[inlet] [noise~] [noise~]
  |       |        |
[expr~ if($v3<=-0.5,$v2,$v1)]

Where <= -0.5 selects the first quarter (25%) of the -1..+1 range used by 
[noise~]. If you remapped [noise~] to the 0..1 range, the threshold would 
become 0.25 = 25%.

  _ _ __ ___ _____ ________ _____________ _____________________ ...
| Mathieu Bouchard - tél:+1.514.383.3801 - http://artengine.ca/matju
| Freelance Digital Arts Engineer, Montréal QC Canada