What does the FM knob do exactly? - Synths & synthesis forums

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Subject: What does the FM knob do exactly?

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Original Message 1/6 18-Mar-04 @ 05:00 PM - What does the FM knob do exactly?

Steve Roughley

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Don't get me wrong, I use it alot, but I have no idea why sometimes it sounds good an sometimes it sounds impossibly awful. What does it do to the oscillators?

Steve.

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Message 2/6 18-Mar-04 @ 06:45 PM - RE: What does the FM knob do exactly?

craig

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It uses the "value" of one oscillator to change the frequency of another osc. It'd be like using a hugely fast LFO to modulate pitch. There are many different algorithms to implementing this, so FM on the Virus sounds different (though similar) to the FM on my Nord.. The Virus FM seems to sound "good" in even divisions of 128 - 64, 76/32 sound a little buzzier, 16/48 etc sound grungier still.. The sync on the Virus nicely evens this out while maintaining pitch, but on the Nord, using sync and FM will throw you completely off pitch depending on the waveforms of the oscs.

I don't have enough technical background into why this is, just my observations.

Even though the FM might sound grungy, buzz, or downright crappy there're still uses for that type of timbre

I find that especially in a bassy sound you can use a tight LPF to just let a little of the grungy character into the sound while maintaining a pretty smooth bass element.

-Craig

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Message 3/6 18-Mar-04 @ 08:42 PM - RE: What does the FM knob do exactly?

Steve Roughley

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Cheers for that Craig. One more thing though. I sometimes find that the FM will only sound good at a very particular setting, 34 or 81 for example, where any adjustment to this, even 1 notch either way, will sound horribly out of tune. I don't suppose you'd know of any way of getting to grips with the reasons for this (any reading material on the theory behind FM or something)? Its just that I'd like to be able to have enough control over FM as to prevent me from having to cycle through all 127 values until I get a good sound (which is all too often the case).

Regards.

Steve.

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Message 4/6 18-Mar-04 @ 11:06 PM - RE: What does the FM knob do exactly?

milan

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google it for fm synthesis. there are some good tutorials out there, if you can stand the math (which i for one cant)

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Message 5/6 21-Mar-04 @ 11:55 AM - RE: What does the FM knob do exactly?

Scorpion

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FM is short for frequency modulation. What it does is simply takes OSC 1 and pitch modulate OSC 2. Like what Craig said its like having a ultra fast LFO. So Frequency Modulation modulates the frequency pitch of an oscilator. Another way to get ring tones and odd metallic noises is using the Ring Modulator. I think its also known as AM short for amplitude modulation. Instead of modulating the pitch it modulates the amplitude or the volume of a waveform of an osc your modulating.

I hope this helps.

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Message 6/6 21-Mar-04 @ 09:32 PM - RE: What does the FM knob do exactly?

Broken Silence

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With 2 oscs, detune at like 90 and FM at 1 makes for a huge trance lead :D

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