As guitarists, as pedal-lovers, we've often heard said "oh, this is a modulation pedal." Maybe you've even said it, yourself. But have you ever stopped to think about what it means? Modulated pedals need .... something to modulate. Do you know what your pedals are modifying or controlling?
Modulated Effects and their Sources
We'll start with some well-known effects, and consider their sources (aka guts).
Chorus : modulated delay
Phaser : modulated filter
Tremolo : modulated amplifier
Flanger : modulated delay
Vibrato : modulated delay
Modulated Delay: .... well, this one seems obvious
We can also think about these effects in block diagram form: In a normal delay, we have something like this: Input gets split between a clean and a delayed signal, which meet again at a mixer. Some of the signal may be optionally sent back through a feedback loop.
In a modulated delay (or a chorus, or a vibrato, or flanger), we take the same block diagram above and add a "modifying or controlling influence" over some portion of it. In this example, we are applying a change to the delay time, which (given a short delay) will produce a chorus effect.
Often, a modulation source will be an LFO (low-frequency oscillator .... a woo woo woo woo), with controls for Rate and Depth (think Chorus). Rate controls how fast we modulate (change) the delay time, and Depth controls by-how-much we change the delay time. New sources are coming out all the time (most recently the OBNE Ramper has been making waves! [ha dad jokes]).
And since modulation is just "modifying or controlling influence", we can modulate any part of a circuit! The filters, the repeats, the bias, the volume, the delay time, the repeats, the repeats, the repeats ... Next time you hear someone say they've got a new modulation pedal, remember it's just an adjective ;) !