KVR Audio

bernhardtjeff · Post by **bernhardtjeff** » Wed Sep 14, 2005 1:04 am

any vsts that do octave stuff with half wave rectification? or by modulating the input with itself to get sum tones or something?

greendoor · Post by **greendoor** » Wed Sep 14, 2005 1:15 am

I've often wondered something similar. Although isn't it full wave rectification that does octaves? This is my understanding: consider a sinewave, swinging negative and positive. Using four diodes in a bridge-rectifier configuration - you convert that AC signal into a pulsed DC signal. In code you would simply turn all the negative cycles into positive cycles. This means that you have doubled the frequency very easily - although you now have an extreme DC bias. Apply an opposite DC bias to convert this back into AC. I think this is how analog octave guitar pedals did it without needing pitch shifting DSP.

I suspect that it's easier and smoother to double the pitch by simply copying each cycle twice. I don't now how standard pitch shifting works, but octaves should be very easy to do, so I would like to see a simple octave pitch shifter plugin that isn't glitchy like most pitch shifters.

bernhardtjeff · Post by **bernhardtjeff** » Wed Sep 14, 2005 1:26 am

jesus, i don't know. you obviously have more background in this than i do! i just heard it called "half wave," but yeah, i guess flipping it to the top would make more sense for octaves. i just want something that does clean octaves, like you said.

Roland Babbage · Post by **Roland Babbage** » Wed Sep 14, 2005 1:27 am

I've no idea what this is about... anyone got an audio example of what this means?

soma · Post by **soma** » Wed Sep 14, 2005 1:53 am

Halfwave rectification = absolute value of X
Full wave rectification is while x > upperlimit || x<lowerlimit then [if x > upperlimit then x = upperlimit -(x-upperlimit)][if x < lowerlimt then x = lowerlimt - (x - lowerlimit)]
Right?

skrasms · Post by **skrasms** » Wed Sep 14, 2005 2:00 am

In electronics halfwave is where you just chop off (ie, block) the negative swings, so it wouldn't be abs(x). As an equation with logic it'd be more like x*(x>=0) so that the output is zero whenever x goes negative.

Fullwave, however, would be abs(x) or ((x^2)^0.5)

shamann · Post by **shamann** » Wed Sep 14, 2005 2:02 am

Well for one octave up distortion, I don't know any specific plugins that would do it that aren't pitchshifters (which aren't the same thing). But you could easily do it in most modulars.

Half-wave tends to be more musically useful. In Synthedit, you have two options: send the sound into a rectifier, then mix 50/50 with dry signal. Or just use the clipper and set the low value to 0 and high value to 10 or up. I prefer method one, that way the signal actually gets a bit louder (due to summing). Other than modular stuff, I don't know of any waveshapers that let you alter the positive and negative phases of a signal independently. I'm sure there is one, I just don't know it.

Not rectification at all, but for suboctave dividing, the best I've found is SubOct by ConcreteFX, available from Jon's free stuff thread.

To learn all about distortion, including applications of both full and half-wave rectification, go here.

soma · Post by **soma** » Wed Sep 14, 2005 2:04 am

Ah ok I was confusing half wave with full wave. Then wat is it called when you bounce the signal at a limit on both sides then normalize?

soma · Post by **soma** » Wed Sep 14, 2005 2:10 am

Thanks for the link. I guess to answer my own questio it is a double partial rectification.

bernhardtjeff · Post by **bernhardtjeff** » Wed Sep 14, 2005 2:37 am

well, in any case, if it's easy, could someone whip one up real quick?

i have no skills to do so. wouldn't need a gui or anything...

soma · Post by **soma** » Wed Sep 14, 2005 2:58 am

Here you go:
http://home.comcast.net/~soma720/shaper.dll

greendoor · Post by **greendoor** » Wed Sep 14, 2005 3:05 am

Nice link - that's mainly discussing distortion for guitars though. Probably not a real smooth octaving effect. Half wave rectification is literally chopping off the negative part of the cycle. I think that would be a bad thing in the digital realm - i'm guess analog stuff would probably not behave as precisely as DSP and might be more forgiving.

Full wave rectification flips the negative into the positive. So a sine wave now has half peaky triangle waves - a lot of harmonics you don't want. You could filter them out.

I don't have any DSP skills, but I have ideas. What do you think about this one: it's going to have a lot latency, but I think it would be really sweet ...

From zero crossing to zero crossing, stream the audio input data into a two buffers (negative & positive sides of the cycle). At the end of each negative cycle, stream that stored data (positive then negative) into the output stream at twice sample frequency, but do it twice. That way you should get a perfect, glitch free octave. A sinewave at 100Hz should come out at 200Hz with no harmonics or glitches whatever. Can normal pitchshifting do that?

soma · Post by **soma** » Wed Sep 14, 2005 3:09 am

greendoor wrote:Nice link - that's mainly discussing distortion for guitars though. Probably not a real smooth octaving effect. Half wave rectification is literally chopping off the negative part of the cycle. I think that would be a bad thing in the digital realm - i'm guess analog stuff would probably not behave as precisely as DSP and might be more forgiving.

Full wave rectification flips the negative into the positive. So a sine wave now has half peaky triangle waves - a lot of harmonics you don't want. You could filter them out.

I don't have any DSP skills, but I have ideas. What do you think about this one: it's going to have a lot latency, but I think it would be really sweet ...

From zero crossing to zero crossing, stream the audio input data into a two buffers (negative & positive sides of the cycle). At the end of each negative cycle, stream that stored data (positive then negative) into the output stream at twice sample frequency, but do it twice. That way you should get a perfect, glitch free octave. A sinewave at 100Hz should come out at 200Hz with no harmonics or glitches whatever. Can normal pitchshifting do that?

I made one of those some where. That is called wavelet resynthesis. I'll look for it tomorrow.

bitcrusher · Post by **bitcrusher** » Wed Sep 14, 2005 3:20 am

I just added this real quick to minion:

http://www.devine-machine.com/minion/minion.dll

in the FX menu there is an option "X Rectify" which adds this, the point-of-rectification on the negative side of the signal is controlled by the corresponding ball's Y axis.

shamann · Post by **shamann** » Wed Sep 14, 2005 3:45 am

Yay, new minion stuff!

Anyway, here's another Synthedit job. Makes a good noise, if not as smooth a noise as an FXpedal might. Please excuse the grade 8-ness of the name, I generally name all SE things I've made starting with SH (my initials) and then the name of the effect.

http://www.sighup.ca/misc/SHOctave.zip

Cheers,
Steve

half-wave rectifier octave vst?