LFO/ring mod question

[edpoulsen]

Ok, so I know what an LFO is, but i'm having trouble understanding it's various uses. As I understood it, an LFO generated a low frequency which could attenuate or accentuate higher frequencies. But on my moog ring mod it appears to affect the "depth" of the modulation. I have a gut feeling that understanding how this LFO works is a big part to understanding how to use synths in general, or in conjunction with each other. So how does an LFO work, what are it's uses (specifically using it's signal as a trigger for say an ADSR or sequencer)? Thanks!

[Bryan T]

As I understood it, an LFO generated a low frequency which could attenuate or accentuate higher frequencies.

I think you are a bit confused. This is a good start: http://en.wikipedia.org/wiki/Low-frequency_oscillation

The Moog manuals are also a great resource for learning about the components used in synthesis.

[Bryan B]

For most uses, the LFO's job is to modulate things. It has a voltage swing (oscillation) that constantly goes up and down from 0-5vDC. When you apply this to the Fooger CV inputs, it is a source to turn your knobs for you. You can even have it move much faster than your hand could ever turn a knob. It has many uses and each one drastically changes the sounds these pedals make.

In the Ring Mod, it modulates the frequency of the carrier oscillator.

[EricK]

Think about your VCO like this:
Its sending out a waveform all the time.

Once you start approaching 20hz, its already getting difficult to register as a pitch. below that its just a click BUT it is still in that waveform that you set it at.

If you had a function generator connected to a speaker with probes around 2hz, you would see the speaker slowly vibrate like it is breathing (if its a sine wave). If you think about that "breath" being your pitch, this is how an LFO works. It is still sending that waveform to your destination.

This is why VCOs with cv and audio outs can double as sound generators AND signal sources.

If you hook the osc out to your guitar amp (really hot signal not reccomended) you would hear a click. Any click that occurs at a rate of 20 times per second (20hz) is a pitch. If you get it up to 20,000Hz, then it is still sending out a voltage that follows the attributes of whatever waveform it is set at.

So,
If you want to make siren sounds, then you switch it to sine (on the ringmod it is really closer to a triangle but marked on the panel as a sine) and send the osc out to a pitch. If you want to make intervals that pulse, then switch over to square wave and you will hear that.

Turn your Ringmods mix all the way to 10 and the freq to 12:00 and your amount all the way up and experiment with the rate of the LFO and hear it affect the frequency.

This is essentially what an LFO does.

If I didn't say anything accurately please correct me.


Respectfully,
Eric

[edpoulsen]

Thanks for all the input, that really cleared up alot for me. Many thanks to Mr. Eric, for helping me understand the given topic once again. If I had gone to Guitar Center, or any other mainstream music store for that matter, with these questions I'd get a blank stare, followed by a long sigh, a little bit of stuttering, and then get lead to the most expensive keyboard synth in the store haha. I'm also considering picking up a basic electrician class at the local community college, I figure that will help alot with the theory. Thanks again

[hieronymous]

On this track, I'm using an LFO (from the MF-103 phaser) to sweep the frequency of the filter on the drone that starts the piece out:

minus prolegomenon

This is of course only one possible use, but it's one that I tend to utilize. Hope this helps!

[EricK]

H,
Man that was a good track! Did you do the drums? Im working on an all Moog album but I can't get Moog percussion (and be able to do it live by myself)

That phaser sounds goooooood!

Im impressed.

E

[hieronymous]

H,
Man that was a good track! Did you do the drums? Im working on an all Moog album but I can't get Moog percussion (and be able to do it live by myself)

Actually the drums are "real" - my buddy Greg DeGuglielmo, an amazing drummer who can play both rock and jazz, so we can make my favorite kind of music - improvised rock!

All-Moog-album - sounds good to me, Moog percussion or no!

That phaser sounds goooooood!

I should have been more clear - I was using the MF-103 LFO, but controlling the frequency of the MF-101 low-pass filter. Actually, now that I think about it, I split the LFO with the CP-251 and split the audio signal from the Rogue, so one channel is the MF-101, and one is through the low-pass filter of the Frostwave Resonator.

In fact, here's a picture!