try to implement a compressor

galaa · 7 Apr 2005

I've been thinking about this as well. You can use the 'Float Less' component which would enable you to compare the input with a threshold setting and as soon as the threshold was lower than the input the component would output a boolean true. You would then trigger your envelope to start compression. However, at the moment there is no way of triggering an envelope; they are started automatically with a MIDI on signal. I think malc & jorge are working on this though so shouldn't be too long.

If anyone knows a way round this feel free to correct me

rl · 7 Apr 2005

you could provide your own envelope, e.g. by using the code component. Have a

monoin trigger;

input, and if trigger > 0 start your envelope processing

to implement abs(x):

float x; float absx;

absx = ( x >= 0 ) & x + ( x < 0 ) & (-1 * x);

galaa · 7 Apr 2005

After playing around with envelopes I've found something that might help. I'll try and explain it best I can. If you set up an amplitude envelope but have it so you can turn it off with a switch. So when the EG is off you multiply the signal by 1 using a selector. Hold down a note with the EG off then switch the EG on and it triggers the envelope. If all the envelopes are triggered by note-on only then it should already have been started when the key is pressed.

If there's a way of 'flicking a switch' with the result of the input/threshold comparison then you have yourself a compression envelope

-Edit- Though I'd stick a picture in just to make it clearer

pdelrieu · 7 Apr 2005

Thanks for your help. I get deaper in the online documentation and I found the syntax and function available in the code component. I didn't see the conditional syntaxe.

For the envelop I will try, I thought about It but without the code possibility I didn't see how.

When I will have something working I will post it.

regards Philippe

Shifrin · 7 Apr 2005

I'd guess you could implement a simple envelope follower in the code component, check out http://www.musicdsp.org for some useful code. Once you've got that you can use it to trigger the AD for the compression, hmm, interesting I might have a look at this if I get the time to see if I can do it. If it's not doable (for whatever reason) I'm sure we'll have the necessary tools to do it soon!

Shif.

pdelrieu · 9 Apr 2005

I made some test for simple compression algo : out = gain*in in compression mode and out= in out of compression mode. I develop the following code : monoin in; monoin thresh; monoin gain; monoout out;

float absx;

absx = ( in >= 0 ) & in + ( in < 0 ) & (-1 * in);

out = (absx>thresh) & gain + (absx <=thresh) & 1.0;

It made a lot of distorsion i think because the switch between compression mode and not is too strict.

I try to develop a simple envelop to trigger the gain or cut the gain after a number of sample. The code is : polyin feedback; polyin nbsample; polyin start; polyout out;

float attack; float remove;

remove =(feedback >=1.0) & feedback + (feedback >=0.0) & feedback; feedback = feedback + (start >0) & (-remove);

attack = 1/nbsample;

out = feedback+attack; out = (out>=1) & 1 + (out<1) & out;

I connect the out to the in feedback but with graph analyser I can't see anything. the feedback is always 0. It is allowed to connect a code module out to the in of the same module ?

I looked for information about compressor and it's more complexe than I thought. The gain depend on the enveloppe of the signal which is calculated using a window of sample. There is no way to have an array of sample ?

regards

Philippe

jorge · 9 Apr 2005

Hi pdelrieu

pdelrieu wrote: It is allowed to connect a code module out to the in of the same module ?

Yeah, that should be no problem due to the 1-sample-at-a-time sound engine of synthmaker.

pdelrieu wrote: There is no way to have an array of sample ?

Not yet, stefancrs has been asking for both loops and arrays. Loops is already done so we're getting there.

We got your email with a crash report, thanks.