octave down?

[school]

simple 1 (preferably one, simpler the better) octave down pedal. i just want to be able to control the mix of the dry signal and the octave. anyone know how to do this or what pedal i should make for it?

[toneman]

Try the PAIA RocktiveDividor.
it's got "the mix".
DIY modernized version  on the Hammer pages.
or, PAIA *still* sells a kit!!!!!   www.paia.com  
stay anoctave Lower
tone

[hank reynolds 3rd]

the schem for the mutron octave divider is around here somewhere (try the search field..)

I think that produces a clean octave...
Im gonna give it a shot soon (in barcelona at the mo, travelling about a bit...)
I think some of the values arent that clear but i think most other oct downs are square wave-y....


Sam
BTW..Havent been here properly in ages...cant believe how big this forums getting!!!  

[R.G.]

I think that produces a clean octave...

It does not, at least not in the sense of a clean, undistorted tone. No octave down generators based on reasonably simple non-DSP circuits do.
all divider style octave downs produce a square wave style distortion in the output. This can be filtered to sound less rough, but it's still there.

[Joe Davisson]

This is fairly easy, but still a little synthy:
http://www.diystompboxes.com/analogalchemy/pedals/shocktave.html

I started an octave-up mod for it once, but I'll ask again, why do octave-ups only work above the 12th fret?? I got a really great, strong octave sound but I want it on the whole fretboard.

[jmusser]

If Joe is stumped, I don't feel so bad asking that question! I've asked it in one way or another several times. It seems like down octaves can be heard across the whole fretboard, but the up octaves only seem to become apparent after the 10th fret on up. One circuit that I've found that is somewhat contrary to that, is Tim's Octup Blender. The up octave isn't as strong on the wound strings, but it is there. The Digital Octaver Fuzz, has been the first one I've built that ghosts in down octave WITH the up octave. On the great thread "How Octaves Work" http//diystompboxes.com/sboxforum/viewtopic.php?p=203448  R.G. talked quite a bit about "audio perception" (I'm paraphrasing). It has to do what the musical note is perceived by the human ear as opposed to what is actually being generated. This could be the whole "problem" with up octaves on the lower frets. Maybe they are indeed there, but our brain doesn't register them, because they are off just enough mathmatically from double the frequency, not to be recognized by our brain. Maybe R.G., Mark Hammer or Doug Hammond will chime in on this one to clear it up for us, if we're lucky. I'm so ignorant about this topic, I don't even know where to go for reference material on it, because most things I've read allude to octaves, but don't dwell on the subject too much. One thing I have referenced to, is the Bobtavia sound sample. I don't know if it's Doug playing on that one or not, but he does what I believe is a pinched harmonic (I have never been able to do one), that sends the note into the stratosphere. I believe, that this has to be a doubling of that note. Why can't we get an effect that starts off at the nut where the 12th fret up octave note normally is, and then be at where the pinched harmonic note was at the 12th fret?

[Mark Hammer]

1) As R.G. correctly and astutely notes, there IS no such thing as a "clean" octave down produced by means of either a CMOS (Bluebox, Rocktave, etc.) or a discrete (Shocktave, Maestro, etc.) flip-flop since the flip-flop puts out a square wave.On the other hand, there is nothing to stop anyone from filtering out much of the nasty harmonic content from that square wave and making it sound "clean" (i.e., closer to sinusoidal than to square).  Many of the variations in sound/tonal quality between makes of octave down units that use a monophonic flip-flop approach are essentially due to differences in the amount and type of lowpass filtering provided for the octave-down tone/signal.

2) Why DOES the capacity of an octave-up unit to nail a clearly audible octave depend on where you play on the fretboard and what strings?  My sense is that this is NOT any sort of psychoacoustic phenomenon, or indeed anything that depends on the fundamental pitch of the note.  Rather, it is a question of the mechanical vibration of strings themselves.  Remember that as you play higher up, not only does the note get higher, but the string essentially gets stiffer too.  That stiffness changes the relative dominance of different harmonics, and also changes howmuch the pitch might be distorted or shifted as milliseconds go by.  Remember that the rectifier approach to making octave-up notes relies on summing the upper (or lower) half cycles of an inverted and noninverted version of the input signal.  Let's call the first "wiggle" of the string the "A" half cycle, and the second one to show up on a scope, the goes in the opposite direction, the "B" half cycle.  The octave effect relies on making a composite out of the A half cycle only from one copy of the input, and the B half cycle from another inverted copy, resulting in two "wiggles" in the same direction.  

If the ONLY thing we feed to such a device is a stable sinusoidal oscillator signal, we WILL get something that sound like double the frequency at the output.  Trouble is that strings are NOT that stable. The longer the string, and the looser, the more likely there will be some pitch distortion, especially if plucked hard.  The question you have to ask yourself is whether the time it takes to move to the next half cycle (i.e., the time between the A and B half cycles) is sufficient to permit any change in the actual pitch of the string (and any partials/harmonics) to occur.,  The answer you will get back is that there is LESS time and opportunity for such loss of summing capability (i.e., the possibility for the A and inverted B half cycles to sum flawlessly and produce double the input frequency) when the string is relatively short and more rigid (i.e., higher frets).

My guess is that where octave-up notes start top emerge on a baritone guitar or a mandolin would be different that where they appear on a standard 25"-ish scale instrument.  My guess is that use of heavier gauge strings or a wound 3rd would also change where octaves starts to appear.

Finally, you will note that octave-up boxes also produce intermodulation and quasi-ring-modulator tones as well when you bend strings.  J.C. Maillet (Mr. Viva Analog) has the math all worked out for why this happens).  Ironically, this also seems to happen in the same string/fretboard zone.

I'd be curious to hear about anyone's experience using same or heavier gauge strings tuned down (the SRV manouver) or simply heavier or even flatwound strings.

[GFR]

I agree with Mark, I think the key is the high notes having less harmonics (because of the response of the strings, pickups, guitar controls, etc.).

Even then to get a good octave sometimes you need to filter out some harmonics by turning the tone knob down (or using some active LP filtering). If you filter low enough so that the low strings have a nice octave, the high strings get too attenuated - there's a compromise.

Some mid storming:

Perhaps a guitar with a hex pickup could have six octavers each one optimized for each string.

Or maybe you could make an adaptative LP filter so that it filters lower for lower notes.

Or, if it's easier to get the octave down working for all the fretboard, use it and that multiply THAT frequency

[jmusser]

My suggestion is to just by the Arion MOC-1. You can probably get it for less than $30.00 at Musician's Friend, and it mixes clean with one and two octaves down. It is very clean, and very pronounced. It tracks well all over the fretboard. I've talked about this inexpensive effect a lot on here, but, it does a great job, and I've always been impressed with it.

[jmusser]

Mark, I am still trying to get what you're saying into my head. If I'm understanding you correctly, the reason the up octave is not showing up on the lower strings, is that the length of the string allows too much time for the lower part of the wave form to duplicate its self accurately. Correct? If that's the case, why don't down octaves have that problem? They track all the way across the fretboard. Is it because the longer string length is more condusive to lower frequencies? It looks like you'd be into the reverse of this with down octaves, where the shorter string length keeps the down octave from showing up on the higher strings. As far as I know, the down octave waveform is flipped under the reference, like the up octave is flipped on top of the reference. Correct? This is why I'm confused that it doesn't have something to do with "psychoacoustic phenomenon" ( I like that phrase BTW). That phenomenon may also be why we don't hear the intermodulation and ring mod weirdness on down octaves. I was mentioning Tim's Octup Blender. It is a weirdo. Since I don't know exactly what's going on with it, I am guessing that the "mix" that's happening there, is that the fundamental is getting sent through and square waved, along with the up octave square wave, and that is why you can hear it over the whole fretboard. I can see how it has the fundamental going it's own direction to mix clean signal with the square waved signals. I'm guessing square wave, because it sure is sythy sounding. It is one of the weirdess tones I've heard. Real eerie!

[Paul Marossy]

I like the Shocktave, it's pretty cool.  

[Mark Hammer]

Mark, I am still trying to get what you're saying into my head. If I'm understanding you correctly, the reason the up octave is not showing up on the lower strings, is that the length of the string allows too much time for the lower part of the wave form to duplicate its self accurately. Correct? If that's the case, why don't down octaves have that problem? They track all the way across the fretboard. Is it because the longer string length is more condusive to lower frequencies? It looks like you'd be into the reverse of this with down octaves, where the shorter string length keeps the down octave from showing up on the higher strings. As far as I know, the down octave waveform is flipped under the reference, like the up octave is flipped on top of the reference. Correct? This is why I'm confused that it doesn't have something to do with "psychoacoustic phenomenon" ( I like that phrase BTW). That phenomenon may also be why we don't hear the intermodulation and ring mod weirdness on down octaves. I was mentioning Tim's Octup Blender. It is a weirdo. Since I don't know exactly what's going on with it, I am guessing that the "mix" that's happening there, is that the fundamental is getting sent through and square waved, along with the up octave square wave, and that is why you can hear it over the whole fretboard. I can see how it has the fundamental going it's own direction to mix clean signal with the square waved signals. I'm guessing square wave, because it sure is sythy sounding. It is one of the weirdess tones I've heard. Real eerie!

Bear in mind that octave-up units are more "analog-ey" and octave-down more "digital-ey" in terms of how they go about producing the effect.  We hear an octave up because the "A" and "inverted-B" half cycles are available and mixed in equal proportion.  We hear an octave down because the note played met the threshold requirements for the flip-flop circuit to trigger.  The second one is far more readily attainable across more of the fingerboard than the first one is.

As for use of hex pickups and polyphonic octave boxes, the old Guild Tri-Oct (circa 1968-1971?) did this, and occasionally it worked.  Trouble is that once you move far enough away from the bridge, there is way too much lateral movement of strings for each dedicated polepiece to sense ONLY the string above it.  Given that hex pickups are often forced to work with smaller, less-sensitive coils, the degree of amplification required for that set-up to trigger a flip-flop can easily result in false triggering by adjacent strings.  As was pointed out to me, this unit probably needed to have, and anticipated use of, heavier gauge flatwound strings that would not budge very much.  Something like those G-Vox pickups, which snuggle right up against the bridge, however, might work fine.

[GFR]

See if this helps:

http://www.gfrhpg.hpg.ig.com.br/octaves2.html

[jmusser]

I think that's gong to help, but I'll need a little time to digest it. Thanks for the link.

[Mark Hammer]

Excellent work, Guillherme!

It got me thinking.  Perhaps the smart thing to do is to precede any octave-up and/or octave down circuit with a nicely filtered TS-type clipper.  That is, compress the signal by clipping it hard, filter out the nastiness in the high end for an undistorted (or at least less obviously distorted) sound, and then feed the signal to the relevant rectifier or flip-flop circuit.

Although your analysis indicates that requirements are different for the two types of circuits, one of the things they DO share in common is more predictable functioning with a symmetrical, consistent input signal.

Of course, the caveat one needs to add to this is that sometimes "more consistent" is not necessarily better from an aesthetic point of view, even if in terms of design it makes some circuits behave more reliably.  It IS, after all, the moment to moment variability of analog that we love so much.

[snap]

Flageolator

[Joe Kramer]

Hi!

If you take ANY rectifiication-type octave box (Octavia, Scrambler, Green Ringer, etc) and feed it a pure sine wave, it will produce a perfect octave from 20-20K. The reason these boxes sound good in the 10th-12th fret region of the guitar and with the neck pickup is because this area produces the closest thing to a sine wave that a guitar can do. If you could get the guitar to make a nice sine wave all over the neck, you'd have nice octaves all over the neck.

This kind of circuit takes the negative half of the signal and "folds" it in half at the zero longitude. After the folding occurs, the negative peaks sit between the positive peaks and you now have twice the frequency as far as the positve peaks of the signal are concerned--an octave. The need for a sine wave here is because, if the peaks are less than even, the folded output looks less and less like exactly double the number of peaks, and the octave effect starts to weaken and sound more like rough fuzz.

That make any sense?

Joe

[StephenGiles]

........which, as I have said on a number of occasions, means that you need to convert your guitar signal to a sine wave - how ------- come on down the EH Guitar Synthesiser front end - a lot of circuitry, but you get a sine wave.
See here:
http://img.photobucket.com/albums/v317/StephenGiles/EHsynth1.gif

......and the answer is no. I don't have a veroboard layout!
Stephen

[Joe Kramer]

........which, as I have said on a number of occasions, means that you need to convert your guitar signal to a sine wave - how ------- come on down the EH Guitar Synthesiser front end - a lot of circuitry, but you get a sine wave.
See here:
http://img.photobucket.com/albums/v317/StephenGiles/EHsynth1.gif

......and the answer is no. I don't have a veroboard layout!
Stephen

Good Lord!  Better just stick to blues in D!

Stephen, I've never seen this circuit (nor have I played an EH guit synth).  I've previously daydreamed of some (much easier) way to sine-ize a guitar signal, but I take it you have actually built this thing.  What are your findings?  Does is satisfy as far as effort-to-usefulness ratio?  In other words, is it worth it?

Joe

[StephenGiles]

It was worth every long hour I spent  building it. This, of course is only the front end, there were 3 tracking oscillators, VCF etc, but the point is it worked. I saw the sinewave produced at EH UK back in 1980. You see it all depends on your point of view, I see no difference in building this from building a dozen fuzz boxes. Just follow the circuit and it will work.

You may not need all of it, I'll have a look.
Stephen