Muff's Modules & More

pvdn

I'm working on a modular synthesizer in flash (here) and have been wondering how to implement fm properly. The question is not a technical one, it's the implementation, how the user can use it, i'm wondering about.

I think what i want is an oscillator with an fm input, and along with that an attenuate knob that affects the input on that (opposed to a construction where the user can precisely affect the frequency but has to use addition and multiply modules to do so). With the attenuator fully opened, what does the fm do exactly? Linear fm seems to be the most interesting method (from what i read), with the carrier frequency modulating in the range cf+x and cf-x. What value should i pick for x, or in other words: with two oscs, both running from -1 to 1, and one modulating the frequency of the other, what should the max resulting freqrange be with the att knob fully opened?

governor blacksnake · Posted: Mon Nov 21, 2011 6:30 am Post subject:

try some different values. use your ears and see what sounds best!

bsmith · Posted: Mon Nov 21, 2011 6:54 am Post subject:

wow man really neat thing you're working on there! bookmarked. i've got the fm sounding pretty good on it with 2 sines and simple amplifier sitting between them now. not sure why you'd want a limit to that top number other than as it 'organically' would be at unity. finer control on the simple amp for doing this would be useful for sure.

pvdn · Posted: Mon Nov 21, 2011 7:16 am Post subject:

bsmith · Posted: Mon Nov 21, 2011 7:24 am Post subject:

speak_onion · Posted: Wed Nov 23, 2011 10:16 am Post subject:

speak_onion · Posted: Wed Nov 23, 2011 10:25 am Post subject:

Hmm, check out here: http://rhordijk.home.xs4all.nl/G2Pages/SoundSources.htm#SoundSources_5 688_999246

General Electron · Posted: Wed Nov 23, 2011 1:25 pm Post subject:

To approach the sound of a DX-7, you need to be able to drive the frequency negative, perhaps as far as -8 * original frequency.

FetidEye · Posted: Wed Nov 23, 2011 2:32 pm Post subject:

wow nice software!

looks really smooth too. good interface

pvdn · Posted: Wed Nov 23, 2011 7:17 pm Post subject:

Morley · Posted: Thu Nov 24, 2011 3:07 am Post subject:

Cool project!

widdly · Posted: Thu Nov 24, 2011 3:37 am Post subject:

Nice software.

For DX7 style Linear FM, the deviation (x in your equation) is dependent on the modulator frequency.

Modulation_Index = Deviation/Modulator_Frequency

Adjusting the level of a modulator in the DX7 varies the modulation index from 0 to 13. The mapping is exponential with more resolution for lower indices.

There is a very good explanation here...

http://www.angelfire.com/in2/yala/t2dx-fm.htm

It is usually easier to implement this as phase modulation. If your oscillator code uses an accumulator, each sample you can add the scaled modulator output to it and wrap the result. That should handle positive and negative frequencies.

pvdn · Posted: Thu Nov 24, 2011 6:18 am Post subject:

pvdn · Posted: Thu Nov 24, 2011 6:46 am Post subject:

jonah · Posted: Thu Nov 24, 2011 2:17 pm Post subject:

I recently started building an FM synth in Five12 Numerology and was pointed towards this paper which was helpful:

https://ccrma.stanford.edu/sites/default/files/user/jc/fmsynthesispape rfinal_1.pdf

I found page 7 which describes uses of FM to create specific instruments sounds inspiring and I'm attempting to make the programming of the synth setup so that the user controls sound characteristics rather then abstractly working with operators and the like. I'm trying to increase the intuitiveness of FM while still keeping the powerful synthesis capabilities.

Anyway, your project looks very cool! Good luck!

jimmyedgar

vlk · Posted: Thu Dec 01, 2011 5:46 am Post subject:

Wow. This is great. Lots of fun. Good stuff!

Aroused by JarJar · Posted: Thu Dec 01, 2011 7:50 am Post subject:

A modular synth in real time over the internet, very impressive!

It looks like you have implemented FM as simply adding an audio signal to a frequency argument, the most simple implementation, and the kind of thing that is natural to do with analog equipment (just plug an audio signal where you'd usually have a haptic rate control voltage).

This works great. But, after a certain amount of modulation, and when using feedback, this kind of most simple FM runs off the tracks- wild DC offsets, pitch changes. Even "dead spots" where it will go silent, in software at least (I have not run into these dead spots in analog and don't know if it happens in analog, it may be a digital-specific problem). So you'll have to implement it as phase modulation, like a DX, to get more options and control. To scale the modulator, multiply the modulator by the index and the index by 1/(2*pi). This will give you a typical range from 0 to about 13*, then ever more racous from there. A module scaling according to pitch (or MIDI note number) according to different curves would be nice, so you can insert it between the index input and the modulator.

And you'll want to modulate the index itself (by velocity, lfos, etc.), very important.

Anyway nice work, bravo!

* index range- the actual amplitude is about .159 of that.

pvdn · Posted: Mon Feb 27, 2012 12:35 pm Post subject:

Thanks for all the advice, i'm working very hard for a new release-version. Quick preview: http://dl.dropbox.com/u/250155/patchwork.png

By the way, i've chosen the path of a fully modular thing with regards to handling notes, meaning i have a volt/oct setting for the system (in the previous version i had modules that sent out note-numbers) and all signals are now within -1 to 1. Oh, and if anyone has ideas on how to implement a fast note-quantizer: let me know smile

Morley · Posted: Mon Feb 27, 2012 2:11 pm Post subject:

I like the look of it..

syntax_tn · Posted: Wed Feb 29, 2012 3:23 pm Post subject:

Looks really sweet. I'm doing something similar in Csound (static modules, not dynamically loadable), the UI looks horrible due to fltk.
Good look for this.

As for fm: whether to choose linear or exponential fm: why not implement/offer both types? It's just one line of code that needs to be altered. Have a checkbox to choose fm type or 2 different modules.

Another UI question: how do you decide whether to use knobs, vertical sliders or horizontal sliders fot the separate controls, any particular reason behind this?

pvdn · Posted: Thu Mar 01, 2012 4:21 am Post subject:

It wasnt my plan to choose only one of those, my question was regarding how to implement both of them exactly. But i think i know what to do now, so i will implements both soon.

Regarding your UI-question: i make the what-control-for-what-parameter-decision myself, based on aesthetics and usability. Some kind of volume will usually be a slider, the rest will be knobs... and there are more and different types. The vertical slider is there because a horizontal one had too much empty space in the module (the module already has a width because of stuff in the titlebar).

The modules all have a handcrafted view, in which i myself have to initialize controls with parameters from the module. My previous version did auto-layout all that, but i've quit that approach because it was too much of a hassle to change stuff to my likings.

Btw, you can play with the version on that screenshot here: http://dl.dropbox.com/u/250155/patchwork/main.swf