## how to scale an LFO control signal for FM

Apr 26, 2012 at 1:15pm

# how to scale an LFO control signal for FM

The sittuation is that I am wanting to scale a {phasor~] generated control signal to apply frequency modulation to a [cycle~]. I have looked at some LFO patches, however, I am a little confused as to the standard ways of going about creating LFOs for this purpose.

For example, should an LFO have a fixed frequency range – and then the lfo is sent to an amplifier to control the amount being delivered for FM? Or should an LFO amount refer to the frequnecy range – and consequently reducing the depth to its minimum turns the LFO off?

For example, I have set up a [phasor~] so that it applies FM bewteen 100Hz to 900Hz, and then patched a multiplier object at the end of this so that you can control the amount of this control signal being delivered for FM. Is this correct? Are there alternative ways of applying LFO?

[phasor~ 1]
[*~ 400] (-1 to 1 x 400 = -400 to 400)
[+~ 500} ( -400 to 400 x 500 = 100 to 900 Hz)

– Pasted Max Patch, click to expand. –
#63230
Apr 26, 2012 at 2:02pm

Hi
I suppose it is largely a matter of taste, in that it depends where you are applying the LFO in your FM algorithm. I’m not sure that there is a “standard way” of doing this, although there are accepted practices for FM synthesis, you can place and scale your LFO’s anyway you like I guess; here’s one simple example, modulating the index of the modulator via LFO (depth and freq control):

– Pasted Max Patch, click to expand. –

There’s a fairly extensive and useful tutorial series, by Gregory Taylor I think, called The Zen of The Silent Patch, floating around the C74 site, that is very applicable here.

Brendan

#228088
Apr 26, 2012 at 3:36pm

the patch is interesting – though I am having difficulty understanding what is happening – particularly due to the terminology like ‘mod index’ and ‘carrier freq.’. I was hoping to look into an LFO that you could gradually mix into a note played by a midi keyboard. Is the patch you provided appropriate for doing that/

#228089
Apr 26, 2012 at 4:51pm

Hi
you mentioned FM synthesis in your first post, so I didn’t want to patronize you by explaining the terminology; carrier freq is the centre frequency of the main carrier oscillator (the [cycle~] below [+~]), the mod index is the amplitude of the (2nd) modulating oscillator – it is often related to it’s own frequency, via a scalar (*~) – and in the patch you can choose either manual mod index, by raising/lowering the value OR LFO modulation of the mod index. You really should explore the synthesis examples that come with Max, they are great fun, more or less simple and way better than pounding the forum for solutions/ideas.

HTH
Brendan

#228090
Apr 26, 2012 at 5:10pm

ps
having looked at your patch, plugging an LFO directly into the frequency inlet of an oscillator won’t give you FM but a related effect called vibrato, it is difficult to control the non-modulated centre frequency. So I edited your patch:

– Pasted Max Patch, click to expand. –

http://cycling74.com/docs/max5/tutorials/msp-tut/mspchapter10.html
and this:

http://cycling74.com/2008/07/15/lfo-tutorial-1-the-zen-of-the-silent-patch/

Brendan

#228091
Apr 26, 2012 at 5:39pm

pps

this explains it:

– Pasted Max Patch, click to expand. –
#228092
Apr 26, 2012 at 5:55pm

Thanks very much – all of that looks very helpful. Where do you find the tutorial database? I have looked under the ‘support’ tab in the Max homepage – but that only seems to provide a limited selection.

#228093
Apr 26, 2012 at 11:06pm

here

[attachment=192264,3776]

which you can also access from within Max

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#228094
Apr 27, 2012 at 9:46am

Hilarious… Thanks for all the help though!

#228095

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