Fm

M

makdaddy

Guest
..hehe same boat here mate.. the mind boggles. usually a bout of random fader n knob twirling comes up with something vaguely interesting lol
 

Abstraction

happy juice
i assume you already know what the basic principle of it is, ie. one oscilator wobbling the pitch of another oscilator up and down real fast. like an LFO routed to the pitch of an osc, but much faster.
as for going any deeper than that, ive tried looking this up myself, and all i can really tell you is not to take anything you read on t'internet about fm too seriously. everyone contradicts each other, some people even contradict themselves. and the only 'coherent' explanations are in algebra as opposed to english.
i eventually got a graphical calculator, one of the maths explanations, and NI FM7 and after lots of playing around i think i have an idea of what it is, so you could try that? otherwise i would recomend getting a book or something. hope that helps.
 

ChrisCabbage

Forum Member
Yeah, I pretty-much have the theory sorted.

I am thinking seriously about FM7. That's actually one of the reasons I'm asking the question...
 

Speakafreaka

Champagne Rouletter
Have you got absynth?

Its a bit like that only more digital sounding. Can't get enough of FM7 myself, Just mash about with it and you'll get something kewl. You can do some really nice subtle stuff with it too, and the presets are quite well done so that you can dismantle them easily and figure out why you've done what.

I find that thinking about the individual components of the sound (and having a very precise sound that I want) really helps in FM synthesis. It is a very logical form of synthesis once you've got it figured out.
 
Purusha said:
Yeah, I pretty-much have the theory sorted.

I am thinking seriously about FM7. That's actually one of the reasons I'm asking the question...

great plugin monster...funny, in my synthesis class yesterday i was teaching the FM7....
its really simple to suss out as long as u know the theory behind operators and carriers. Also FM7 goes that 1 step further as you can use loads of waves not just sine waves, lke the old FM keyboards....and also lets you filter in a traditional subtractive way if you want.

if your gonna shell out for it the manual is actually really good and easy to read...thats all i did..also study the preset patches.
 
Double_Helix said:
i assume you already know what the basic principle of it is, ie. one oscilator wobbling the pitch of another oscilator up and down real fast. like an LFO routed to the pitch of an osc, but much faster.

not entirly true.
FMsynthesis involves using the VOLUME of one waveform to modulate/add harmonics to the FREQ of the other. It does not modulate pitch frequency. Thats not to say you cant do that with an LFO in the FM7, but bona fide FMsynthesis is about FREQUENCY MODULATION, not pitch.
 

Sturdy Pete

Sturdy Member
FM is a bit of a nightmare to explain, or even understand. Despite having studied this as part of my course, i wouldn't be able to explain properly without lots of diagrams and some nasty-looking maths. all i can say is that for me, i didn't really get my head round it until i started thinking in the frequency domain instead of the time domain.

after a bit of googling, i reckon this is probably the best explanation of the theory:
http://en.wikipedia.org/wiki/Frequency_modulation_synthesis
(also look at the link to frequency modulation)

and as for the FM7, this appears to be a fairly good explanation of the operation of that type of FM synth
www.computermusic.co.uk/tutorial/fm/fm1.asp

probably the best way of understanding it is to play around with a simple dual oscillator synth capable of FM, until you have a vague idea of what to expect and what can be generated just using 2 sine waves, before trying anything more complicated!
 

Sturdy Pete

Sturdy Member
cameron-nagualsound said:
not entirly true.
FMsynthesis involves using the VOLUME of one waveform to modulate/add harmonics to the FREQ of the other. It does not modulate pitch frequency. Thats not to say you cant do that with an LFO in the FM7, but bona fide FMsynthesis is about FREQUENCY MODULATION, not pitch.

er, no. pitch = frequency

i think your getting FM confused with PM (PHASE modulation), which is how the yamaha DX7 worked. PM a lot easier to implement in a DSP, but mathematically identical to FM once you go through all the maths

(frequency is the derivative with respect to time of phase. i think. aargh! need to look in my notes again)
 

Speakafreaka

Champagne Rouletter
Think of it as Frequency of the modulator alters the pitch of the modulation, and volume alters the amount of modulation.
 
Sturdy Pete said:
er, no. pitch = frequency

i think your getting FM confused with PM (PHASE modulation), which is how the yamaha DX7 worked. PM a lot easier to implement in a DSP, but mathematically identical to FM once you go through all the maths

(frequency is the derivative with respect to time of phase. i think. aargh! need to look in my notes again)

okay...let me re-read...
interesting PM and FM being mathematically the same..thats vry usefull to know.cheers.....but what you HEAR is the blatant addition of frequency overtones to the fundemental..ie a sine wave changing ,by addition of harmonics, into a sawtooth....as opposed to a fundemental pitch modulation....if ya get me...

something.
 

Sturdy Pete

Sturdy Member
yeah i think you know whats going on, but your explanation was a bit skewiff.. let me google some more see if i can find a site with some graphs that explain it..


http://www.indiana.edu/~emusic/fm/fm.htm
(the second graph down)

shows the sidebands generated by one sine being modulated by another.. so from a simple spectra (the sinewave) you end up with a complex spectra, the top half of which is the same as that of a saw wave - but there are also sidebands below the carrier... by using more complex waveforms as either carrier or mudulator, ever more complicated spectra can be generated..

in short, Fm is a can of worms, only truely understood by the extra-clever (ie not me) by means of lots of maths :Sad:
 

ChrisCabbage

Forum Member
Hehehe.

Thanks for the input guys.

I understand the theory a bit, but always found it hard to apply in practise.

Yeah - I use Absynth quite heavily, I know my around it quite well.
 

realisation

Junior Members
Good FM synths to check out: Operator (an ableton live synth) and Rob Papen Blue, and of course FM7. I've got a DX200 which is a pretty good hardware FM synth groovebox as well,

FM is all about modulating one frequency (operator) with another in terms of amplitude, there are different pre-set modulation routes that the sound can take, if you change these you can totally change the character of the sound. FM sounds are usually pretty harsh, and will need a lot more eq than ordinary synths to fit in a mix.

The FM Depth and the decay are sort-of your equivilants of resonance and cutoff in the FM world, especially cool when you change these parameters separatly on each operator (and add a bit of stereo delay etc.)
 

Faction

Proto-col
cameron-nagualsound said:
okay...let me re-read...
interesting PM and FM being mathematically the same..thats vry usefull to know.cheers.....but what you HEAR is the blatant addition of frequency overtones to the fundemental..ie a sine wave changing ,by addition of harmonics, into a sawtooth....as opposed to a fundemental pitch modulation....if ya get me...

something.

With all due respect Cam, "fundamental pitch modulation" is exactly what it is, hence its name - Frequency Modulation. Modulating the frequency (or pitch!) of one audio-frequency oscillator with another (also at audio frequency) has the effect of generating extra partials either side of the carrier frequency whose distribution and level are related to the frequency and level of the modulator. The greater the modulator amplitude, the wider the distribution of generated partials (think about it...).

I can kind of visualise it for simple FM but anything over 2 operators in series and my brain turns to cheese, and trying to visualise operator feedback brings me out in hives.
 

Abstraction

happy juice
it can be easily demonstrated with fm7:

make an init patch, turn on two oscilators, say A and F.
route A through F and F to the output so that F is the carrier and A is the modulator and there is nothing else going on at all. now turn the frequency ratio of A down to 0.0100 and leave F at 1. this means whatever note you play, F will be oscilating at the conventional frequency assigned to that note and A will be oscillating at 1/100 of that frequency. make sure the modulation amount of A on F is at max then play a note. the tone that is being output by F (the only signal that reaches the output) is clearly wobbling up and down in pitch (frequency). in simple terms, that is what FM is. and if you think about it, if that effect is perceivable as an oscillation at sub-audio frequencies, as soon as you move it into audio frequencies, it is still perceivable but as extra harmonics rather than wobbliness.
 
Colin OOOD said:
With all due respect Cam, "fundamental pitch modulation" is exactly what it is, hence its name - Frequency Modulation. Modulating the frequency (or pitch!) of one audio-frequency oscillator with another (also at audio frequency) has the effect of generating extra partials either side of the carrier frequency whose distribution and level are related to the frequency and level of the modulator. The greater the modulator amplitude, the wider the distribution of generated partials (think about it...).

I can kind of visualise it for simple FM but anything over 2 operators in series and my brain turns to cheese, and trying to visualise operator feedback brings me out in hives.

thats the clearest definition ive come across:Smile3:...

funny though..that is excactly what i was trying to say...but managed to say the opposite!! terminology is so delicate..
when i said Fundemental Pitch Frequency I probably should have said that you dont HEAR a change in pitch you hear a change in tone....even though pitch is being modulatd by pitch...
 
Top