Hello, I am super new to Pd but have been using Audulus for about a year. I was thinking about getting a guitari and critter organelle so I could load my own patches in a hardware device and thought I would see how well I could get on in Pd. I'm a lost at the moment, and while I plow my way through hours of tutorial videos I thought I might ask for a little help.

How do I send a waveform of varying amplitude through this expression in Pd?

2 * asin( sin( x *(pi/2)))/pi

@robertsyrett Hi and welcome to the forum and Pd.

I suggest you look at the [expr~] object and its help file. You can run a signal through an expression (using the variable "$v1" in place of "x").

@weightless said:

@robertsyrett Hi and welcome to the forum and Pd.

I suggest you look at the [expr~] object and its help file. You can run a signal through an expression (using the variable "$v1" in place of "x").

Thanks! good to know a little more about how the expression node works. However it doesn't seem to recognize pi as a constant. Should I just substitute 3.1415926535897932384626433832795028841971693993751058209749445923078164062, or is there a more elegant solution?

w00t! I made a basic patch, achievement unlocked

@robertsyrett Nice! I don't know how to convert Pi into something that expr calculates rather than using the super long number. Let's wait if somebody more knowledgeable can suggest a more elegant solution.

"acos(-1)" and "atan(1)*4" might be close enough approximations

@weightless "acos(-1)" might be more characters than "pi" but far far fewer than 3.1415......... And it still seems to work fine, thanks again!

Trying out some things with this expression, it seems to me that all this part does asin(sin(x *(pi/2))) is to map values between -1 and 1 to a range between -90 and 90. Calculating this part sin(x*(pi/2)) with values for x between -1 and 1, and using an arcsin calculator, for -1 I got -90, for -0.5 I got almost -45, for 0 I got 0, for 0.5 I got almost 45, and for 1 I got 90.
So, if you're using values for x between -1 and 1, you could probably replace this with a mapped version of x, and the whole thing could be written like this:

Otherwise, if you want to use [expr], you should save the 'pi' value to a [value pi] (also abbreviated [v pi], where 'pi' is the argument), and then use it in [expr] with its variable name. Mind though that [expr~] is pretty CPU hungry, especially when it comes to hardware like the Organelle.

I might be wrong about the whole arcsin thing though...

@alexandros would three variable wave oscillators and my wavefolder really overwhelm the organelle?

Yes, the idea of a wavefolder is to reflect the waveform when it exceeds the range of -1 to 1. So the plan is to send the wavefolder a waveform and offset that signal by a varying amounts and multiply it's amplitude many times so that it goes outside -1 to 1 and folds back on itself creating new harmonics. If you open the patch I made you can see what it does. A very similar wavefolder would be sin( $v1 * asin(1)) or even cos (x) but I like 2 * asin (sin( $v1 * (pi/2)))/pi because it has more harmonics.

I would love it if you could upload a patch of your atan concept, I'm still hungry to learn how Pd works and practical examples I can relate to would be welcome.

@robertsyrett this was his cleaver suggestion on how to use "pi" inside expr

the object [value] (also called [v]) lets you store a float (like [float]) but you can give it a name and use that name inside [expr] to recall that value. Just make sure the name doesn't contain mathematical symbols like + - . etc.. and also the name can't start with a float, so calling a variable "1pi" won't work, whereas "pi1" will. This is important if you need the name to include $0 (which is internally converted to a unique number for each instance of the patch), remember not to put $0 at the beginning of the name (so you would use pi$0).

Hope this makes sense.

@weightless It is starting to. That is a very different paradigm than Audulus. If I had a patch with multiple wave folders would each one need to have a separate variable, like $v1 in one and $v2 in the other?

@robertsyrett You can use different variables inside an expr object, and they refer to the corresponding inlets. For example if you have [expr~ $v1 + $v2 + $f3], the object will have 3 inlets, the first two are signal inlets ($v refers to a signal) and the third will be a control inlet ($f refers to a float). The help file for [expr] is very useful for that, and you can find further information here http://yadegari.org/expr/expr.html

When you say different wavefolders, I would assume you mean different equations as the [expr~ asin(sin($v1 *(pi/2)))] object is itself the wavefolder. The $v or $f variables refer to the object's inlets.