Octave Up Achieving... Ideas, Thoughts, Experience & Theory?

[Pedal love]

Hmm my circuit was slowly creeping towards what I wanted... but I have none of the funds to get into these territorys at the moment and tbh, I really think it has been decided here that just buying digital is easier (even though I already knew that and have a digital octaver) so I guess I shall forefit from what has been said and maybe just run off what i've started into something else if funds permit.

Thanks for all the comments though and keep them coming as i'd still like to hear your ideas, perhaps i'l pick it up again when I get the motivation.

Ya know Scruffie, these guys definitely mean well, but if I listened to everything they said i wolld stay in my room all day with the lights off. You do what your heart tells you.

[Cliff Schecht]

Hi
RE: ideal rectifier

I don't think I've seen the last one done though.

Quite a few of us have done this and been disappointed. 

I forgot to mention above that if you use the guitar signal as the modulator in a ring modulator (especially a dodgy transformer-based one), you get interesting octave results.

You can also use the guitar signal to drive the switch in a balanced modulator.  e.g. drive a 4066 bilateral switch from A to B (and back), where A is a +ve phase signal and B is a -ve phase signal.

I can see why a precision rectifier STILL wouldn't sound any better than a passive transformer/diode octaver circuit. Even with the diodes completely on, you're going to run into that same nasally and distorted frequency-doubled signal.

One of my favorite effects is a ring modulator (true transformer/diode with op amp buffers) being fed by a Whammy. One output of the Whammy (wet) goes to one input, the dry goes to another. As you pitch shift between one octave to the next, you get some fan-frickin-tastic ring-mod results! At the perfect octave up and down, you get a great sounding distorted octave up or down. Very cool stuff - I found the octave down especially powerful for "stoner rock" type stuff where you want those thick, drony sounds. This was actually my very first pedal design (I posted it forever ago) and is still a staple of my pedalboard.

[Pedal love]

We should have a contest. The best fwr octave up device that anyone can build. I'm sure a lot of you are game. How about it Aron?

[Scruffie]

Ya know Scruffie, these guys definitely mean well, but if I listened to everything they said i wolld stay in my room all day with the lights off. You do what your heart tells you.
[/quote]

Cheers man, yea I know they mean well infact without there comments I wouldn't know what the hell I was doing! I guess i'l keep at it slowly to get what I can eventually (money seems to be a biggg issue) but it does seem like a hard task to get something close to or exactly right.

We should have a contest. The best fwr octave up device that anyone can build. I'm sure a lot of you are game. How about it Aron?

Now that would motivate me, I really like that idea but i'd probably need about 2-3 months to carry on with my circuit annoyingly and I just don't think I can wait that long to see everyone elses lol, so I'd probably have to duck out, or just put the begginings of mine on, but I'd like to see that.

[Taylor]

We should have a contest. The best fwr octave up device that anyone can build. I'm sure a lot of you are game. How about it Aron?

Er, didn't we just do that?

http://www.diystompboxes.com/smfforum/index.php?topic=75373.0

[Scruffie]

So you did ! Didn't see that one, althought that one did allow for fuzzy octaves, not just clean ones. But as my octave progresses I will put it up.

[puretube]

"Elektor" magazine published a multiband FWR octup ~20 years ago...

[puretube]

"Elektor" magazine published a multiband FWR octup ~20 years ago...

Actually, the "VocoderMan" Homer Dudley did it similarly to that way with toobz, ~72 years ago... 
(though not for deriving octave-ups, but "just" CV`s...)

[earthtonesaudio]

One more for the fuzzy octave stuff:
http://www.geocities.com/tpe123/folkurban/fuzz/dof.gif
A good explanation of the technique with some hints for tweaking:
http://www.maxim-ic.com/appnotes.cfm/an_pk/881

[brett]

Hi
I wonder why that circuit has two 1N4148s for clipping/squaring up the output?
Anyone know why? (or have this circuit made up and willing to cut the connections and report the changes?)
cheers

[snap]

volume limiting to .7V?

[earthtonesaudio]

volume limiting to .7V?

That's probably it.  Or perhaps to add some additional harmonics even at heavy filter settings.

[mrslunk]

To ressurrect an old thread..
i've read snippets of stuff in the digital land about pitch shifting achieved by modulating a delay line with an lfo...
anyone know much about this technique and whether it's possible using bbd's?

[Taylor]

Yeah, it's called vibrato.

If you want real pitch-shifting, where you play a C and out comes a G, that's much, much harder than simply controlling a delay line with an LFO. There is the A/DA Harmonizer, which used BBDs I think. You can read about it here:

http://hammer.ampage.org/files/Device1-4.PDF

[mrslunk]

vibrato is modulating with a sinewave or triangle lfo, right?
from what i understood, they (and i can't seem to find the "they" again, it might have been in a dsp book) talked about having a delay line modulated with a ramp up sawtooth.
thanks for the link to the A/DA harmonizer, i'll see if i can find some info and get back

[Taylor]

Well, you can have vibrato using any LFO shape. This line of thinking makes sense, because anyone who's play with delays knows that it's possible to pitch shift when the read time and write time are not the same. But there's a difficulty: to shift one octave down, for example, you have to read at half the speed you wrote. For delay pedals, that means slowing the time knob from e.g. 125ms to 250ms. You get a pitch shift and you think, "I just have to do this over and over and I have a pitch shifter". The problem comes because you have to keep turning the delay time longer and longer, and eventually your delay can't go any further; you run out of time.

So you have to get that time back to the short setting. But if you do it the same way you went down, you'll obviously get a pitch shift up, which most people don't want. So you make that upswing as fast as possible. There's your ramp wave, but it's not so much a ramp, more like stairs that suddenly drop off suddenly, or downward stairs ending in a wall. You don't want the ramp part to be linear, because then you have the "been shot with tranquilizer" sound that gradually pitches down. So you want a quick, vertical drop, followed by a plateau, drop, plateau, drop, plateau, several times, then the whole thing goes back up almost instantaneously.

I don't know why digital guys would ever do this, because there are always going to be a ton of artifacts and chirps. There are better and easier ways to do digital pitch shifting - see Whammy. The only reason I see this as being of interest is for analog loyalists, or people who want a challenge, or people who like lots of quirks. I'm the last type, so I'll be eager to hear what you make... 

[Taylor]

Oops, double post. Was trying to correct some grammar mistakes in the above post (I wrote this right as I went to sleep). Why can't you delete messages here?

[Taylor]

Thinking about this further, you can rather easily make a sort of pitch shifter with a much simpler LFO driven delay than what I talked about before. The key is that you have to be willing to have both an upper and lower shifted note.

Using a square wave LFO to control delay, you get alternating up and down shifts, which I believe would each be equal in distance from the original note. By using very fast LFO time, you can get them to sound as if they are both on more or less simultaneously, but with a hard termolo applied to both the up and down shifted notes. What's cool about this approach compared to pitch tracking VCOs (besides polyphony) is that you can have continuously variable shift range, rather than only shifts that are simply number ratios, as in frequency division.

One problem with the PT2399 is that even with an instantaneous change in resistance, the chip has an inherent portamento. Might be a more noticeable problem at high LFO speeds.

I just simmed this in my DSP program - works well. Doesn't sound like a PS-5, but if you want that, why not just buy one?

[Top Top]

I read that os mutantes had a guitar with six pickups (one for each string) - what about a six pickup guitar with an analog octave circuit for each string? Wouldn't that fix some of the inter modulation issues? 

[earthtonesaudio]

I read that os mutantes had a guitar with six pickups (one for each string) - what about a six pickup guitar with an analog octave circuit for each string? Wouldn't that fix some of the inter modulation issues? 

Yep.  That's the basis for most "guitar synth" stuff.  I think they're commonly called "hexaphonic" pickups.