Why not HFO?

[caeman]

We have Low Frequency Oscillators (LFO) and Voltage-Controlled Oscillators (VCO). These are two common methods for various modulation effects to control the sweep pattern.

But I've never seen High-Frequency Oscillators (HFO) mentioned.

Is the LFO sufficient for that method? Does the HFO have downsides making it unsuitable?


These are the kind of questions that float in my mind.

 

[TomA1234]

I would presume that an HFO would have an oscillation rate too high to be useable or hearable. (by hearable I mean you wouldn't be able to hear the individual oscillations)

 

[Tim_Mofunk]

LFOs are used because they have sub sonic frequencies. If you used an oscillation rate in the audible range 20Hz - 20kHz the oscillation would produce an audible tone. A tremolo with a rate of 440Hz would ring out with an audible A.

It would be fun to try a few things out like having the rate of the HFO track the frequency of the incoming note. It would turn into more of a synthesis experiment than anything else. Chorus would not sound like chorus. Vibrato would not sound like vibrato. I assume (having never tried) that most effects would end up having a ring mod synth like tone.

Just my humble opinion with no experience using a 'HFO'

 

[Pollinator95]

I would presume that an HFO would have an oscillation rate too high to be useable or hearable.

This. 1Hz = one cycle per second. A reasonably sped phaser is probably 0.75Hz, and that's subsonic. [DEL]HF usually means radio frequencies, so over human hearing range [/DEL](~20kHz!). Imagine a phaser that changes from low to high resonance 20,000 times per second!

I don't know about what Tim says. I'm not saying it wouldn't make an audible noise, I honestly don't know.

 

[RickenBoogie]

Correct responses above. An LFO is ideal to "wobble" a sound, as the LFO is inaudable, but anything other than an LFO is, by default, an HFO, though that term is not needed, as "oscillator", or VCO, DCO, etc is sufficient.

 

[bongomania]

Adding to that, one might think of harmonizers, octave-ups, and ring modulators as "HFO" effects, in that they add (or multiply) audio frequencies on top of your original signal. (Only saying HFO for convenience to the thread--RickenB is right about the terms).

 

[FilterFunk]

Good question, caeman! I've wondered about this myself.

Also, would a MFO (mid frequency oscillator) be usable? I'm asking as someone who knows nothing about the science behind any of this.

 

[bongomania]

Here's how it breaks down: if the waves are below audio range, it's an LFO. Anything within or above audio range is what we've described in the previous posts.

 

[boomertech]

LFOs are used because they have sub sonic frequencies. If you used an oscillation rate in the audible range 20Hz - 20kHz the oscillation would produce an audible tone. A tremolo with a rate of 440Hz would ring out with an audible A.

It would be fun to try a few things out like having the rate of the HFO track the frequency of the incoming note. It would turn into more of a synthesis experiment than anything else. Chorus would not sound like chorus. Vibrato would not sound like vibrato. I assume (having never tried) that most effects would end up having a ring mod synth like tone.

Just my humble opinion with no experience using a 'HFO'

True. I experimented with a tremolo type of circuit where I changed the rate with a signal generator. When the speed of the rate generator was in the audible range it came through with the signal and didn’t sound like a trem at all.

I also experimented with an aggressive FET type of clipper that had a set amount of delay reacting to the signals leading edges. The delay gave me this same odd tone everywhere on the fretboard until I shortened the delay so that it was above my hearing range.

-Frank

 

[cheapbasslovin]

I've heard some chop trems that start to sound like a ring mod when they reach their peak oscillation (or at least based on the clips I've heard, haven't used them personally). I imagine that is the sound of an LFO reaching the threshold of an HFO.

 

[BawanaRik]

Moog points out that their Ring Mod can also work as a trem or a phasor. Alot of these mod devices are the same but on different points of the curve. Kinda of like a OD, Distortion and Fuzz.

 

[bongomania]

An image that helped me understand this is an old motorcycle being started up and then driven off. It goes:

gugugugu
gugugugu
gugrrrapp-app-app-app-
ap-ap-apapapappppppnnnnneeeeeeeeeeeeeee! (speeding off)

It starts off with a rhythmic cycle so slow that we can count the beats, and it sounds low like a kick drum. As the cycle speeds up, it becomes more like a drum roll, hard to count the beats, and it takes on a higher tone. Finally the beating cycle gets so fast that it blurs together into a "solid" non-rhythmic singing/whining tone. The faster the cycle revs, the higher the pitch.

One last pedantic (sorry) tidbit about the terminology:

We have Low Frequency Oscillators (LFO) and Voltage-Controlled Oscillators (VCO).

Actually an LFO is a VCO (or DCO, for "digitally controlled"). A VCO/DCO can be any frequency range, including LFO. The term "VCO" is like saying "gas powered motorcycle"--it doesn't refer to the speed. The reason synths have separate sections labeled VCO/DCO and LFO is only to distinguish the LFO one as especially slow.

 

[Explorer]

Moog points out that their Ring Mod can also work as a trem or a phasor. Alot of these mod devices are the same but on different points of the curve. Kinda of like a OD, Distortion and Fuzz.

This. It's a form of ring modulation, which I believe is a form of amplitude modulation (AM). Just like frequency modulation (FM) synthesis, if the carrier frequency (the signal to be modulated) and the modulator (the frequency applied to it) are related, then you get something musical but new, and if the two frequencies are unrelated, the sound is less so (or not at all).

Many ring modulators have an oscillator which is independent of the carrier signal's pitch, which means you move in and out of that harmonious relationship depending on what you're playing. However, if you shift the pitch of the original signal and then apply that as the modulator, you get ring modulation which tracks, and which always has the same kinds of partials as you play up and down.

If you play more than one note with the pitch-shifting modulator on, you'll still get cacophony.

----

Short answer: A HFO results in ring modulation.

 

[RickenBoogie]

An oscillator, (won't use the term HFO, as it is not necessary), does not always end in ring modulation. It can be applied in many ways, most commonly on synthesizers, as the sound source. They can be manipulated many ways as well, with ring modulation being ONE of MANY.