How Octave Pedals Work

It’s a Miracle

The collision of art and science is one of the reasons music is so beautiful. Known as the “basic miracle of music,” the Octave is one of the best illustrations of those worlds colliding.

Picture being in a choir rehearsal. The director tells the sopranos that they have the melody. Then, the director tells the basses that they will be singing the melody an octave down. The miracle of the octave allows the same melody to be sung in 2 different registers; the high floating soprano, and the low-rumbling bass.

How can that be?

Imagine a piano keyboard. If you start on an "A" key, and go up 12 keys (12 semitones/half-steps) you'll find another "A" key that sounds an Octave higher. The same thing happens if you go down 12 keys, but that "A" key will be an Octave lower. When you go up the octave, the frequency doubles. When you go down the octave, the frequency is halved.

We visualize sound using sine waves plotted on an XY plane.

The X axis represents time.

The Y axis represents amplitude (loudness).

We can measure frequency by reading the distance between the crests (top of wave above 0) of one full wavelength cycle as it travels down the X axis.

Let’s go back to our piano keyboard illustration.

When we’re not using a clef and staff, octaves in music are notated by giving the pitch name and number. The lower the number, the lower the octave. On a full 88-key piano, A0 is the lowest key. C8 is the highest key.

With that in mind, look at this illustration.

You can see the 2:1 ratio at work. Each time you go up an octave, your wavelength (measured in Hz) doubles.

In the case of Octave Effects like our Octopus pedal, 2 octaves are generated. 1 is an octave higher than what you’re playing. The other is an octave lower.

To achieve the higher octave, the pedals internals rectify the negative part of the waveform (often called “folding up”) to create a new waveform an octave higher than the pitch you’re playing.

To achieve the lower octave, the pedal converts the signal into a square wave, and then uses flip-flop circuits to divide the wavelength by 2.

So… is your head spinning?

To put it very simply, the pedal has to synthesize these octaves using your original signal as its starting point. This is what makes it different from many other modulation pedals that use a combination of pitch and time offsetting to create effects like chorusing, flanging, tremolo, etc.

Everyone from Hendrix, to Prince, to The White Stripes have used octave effects in their music. Some people use it subtly to thicken their tone. Others crank it way up for far out voicings.

How do you use yours?