Octave up & down advice please....

[brokenstarguitar]

Hey guys i need a little help here. Ive been searching for a good layout for an octave up and down together but havent really found anything. I can find a basic octave up by itself but the sub has me running around. Every sub i find seem to be somewhat involved in synth, all have the nintendo thing going on. Now if theres not a good layout for both together, that you know of, could you suggest a decent sub layout? My goal is to have an up and down with a clean blend. Thanks guys!

[R.G.]

Search for:
Rocktave Divider
Blue Box
MXR Octave Divider
"octave divider" in general

The octave up stuff is universally based on either full wave rectifiers or DSPs, excepting only the JFET Doubler and MOS Doubler I did. There may be a few IC multiplier based ones, but they don't see a lot of use.

You may not be happy with either one. Octave up pedals based on full wave rectification produce an octave, OK, but also a slew of other harsher sounding distortion products. It's a distorted octave up. Filtering may help some, depending on what you're looking for.

Octave down is almost universally done by squaring up the input signal and feeding the square wave to a digital flip-flop. This produces an octave down, all right, but again, it has a lot of distortion products in it. And it's always the same loudness. Filtering may help the square wave harshness, but good octaves down have some way of introducing a believable "envelope" of loudness on the octave down. The Roctave Divider is quite old, but in my mind it's the best simple divider.

I did an enhanced version of the Rocktave that squared up the signal, then used a phase locked loop to produce many higher frequencies as well as two octaves down from the original. This can be used with resistor networks to get a sawtooth waveform, not a square wave. That sounds a lot more like music. I don't know if anyone ever built one.

[EBK]

The real problem with analog (or pseudo-analog) octave effects in the present day is that, although you can always appreciate how they work, you can never really impress anyone who is unfamiliar with how they work.  Build one to learn and to have some quality fun (note carefully that I am not saying this is a waste of time at all), but then buy a POG and be blown away. 

[Danich_ivanov]

I agree with both of these statements, if you want an octave fuzz - go analog, but for clean octave, digital is the way to go. Clean analog octave is a tough thing to produce.

[Mark Hammer]

The eternal challenge with analog octave-shifting, I have come to believe, is our collective tendency to use lighter gauge strings.  Both octave-up AND octave-down behave themselves better, and more reliably, when one is using stiffer strings with less harmonic content, and/or playing above the 7th to 9th fret, where the shortening of the effective length of the string also damps harmonics, and puts the fundamental out front, where the octave-conversion circuitry can do its job well.

As R.G. wisely notes, octave-down neglects dynamics (and even "wants" undynamic input for reliable triggering), suggesting that some sort of companding (or at least upward expansion for the octave-down section) improves performance by preserving input dynamics.

On a related note, has anyone ever measured what the gap/lag is between input and the pitch-shifted output components is on digital octave boxes?

There IS a tonal certain charm to what analog produces, but as Danich also wisely notes, a simple Nano or Mini-POG will offer more reliable and trouble-free performance with fewer headaches.  Having said that, I recently added a 2nd hand Mooer Pure Octaver to my arsenal, and I don't know if it's me or what, but it sounds just a cent or two flat to my ears.

[R.G.]

As always, Mark, great and thoughtful analysis. I couldn't agree more.