Octave effect

Octave effectboxes are a type of specialeffects unitwhich mix the input signal with a synthesized signal whose musical tone is anoctavelower or higher than the original. The synthesised octave signal is derived from the original input signal by halving (octave-down) or doubling (octave-up) the frequency. This is possible due to the simple two-to-one relationship between the frequencies of musical notes which are separated by an octave. One of the first popular musicians to employ the octave effect wasJimi Hendrix,who also used a variety of other effects in his recordings and public performances. Hendrix used an octave-fuzz pedal known as theoctavia.

Analog octave effects differ fromharmonizersandpitch shifterswhich digitally sample the sound and process it to change its pitch.

Creation of the octave

Octave up

Octave up by rectification

Octave-up effects usually use full waverectificationusingdiodesto "fold up" the negative part of the waveform to make a new waveform an octave higher in pitch.

Octave down

Mark Bass Octaverpedaldemo onbass.(Octave down).

Octave-down effects are typically produced by converting the signal to asquare wave,and then usingflip-flopcircuits to divide the frequency by two. This creates a buzzy synthesizer like tone. TheMXRBlue Box used this method to create a two octave drop (expanded to include one octave down in later re-issues).Jimmy Pageused a Blue Box to record the solo onLed Zeppelin'sFool in the Rain.

MXR Bluebox (reissue model), an octafuzz producing octave down tones.

TheBossOC-2 unit generates tones at one and two octaves down from the input signal. This effect also uses flip-flops to generate square waves at 1/2 and 1/4 of the input signal frequency, but rather than simply mi xing in these signals, it uses them to invert the polarity of the input signal on every other cycle (every two out of four cycles for the second octave). This effectivelyamplitude modulatesthe input signal with a carrier at half the input signal, creating new frequency components at 1/2 and 3/2 the input signal. The 3/2 component is low-pass filtered out. This more complex approach lessens the synthetic sound of the octave tones by making them more closely associated with the original signal, and also makes the effect volume-sensitive.

TheBossOC-3 (2006) has an additional mode called "Poly" where only a low note is added with the idea to add a bass line to chords. In 2020,Bossreleased the OC-5 which included features from both of the previous versions, as well as some new ones including octave up, poly/vintage mode, source switch and superior tracking engine.

TheMu-tronOctave Divider (about 1972) had a unique generator that tuned into the low octave as long as the input signal was strong and then continued generating the same frequency while that input signal faded.

Use of octave effects

Octave pedals can be used in conjunction with fuzz (seeoctafuzz) and/ordistortion.It can be used on guitar to make it sound more aggressive (such as the lead-in solo byPrinceonWhen Doves Cry) or sound like a bass. The songSeven Nation ArmybyThe White Stripesfeatures an octave pedal on electric guitar, simulating the sound of a bass.