Even Order harmonic pedal

[Krunchy2]

I was wondering if anyone knows of a fuzz or distortion pedal that that produces only EVEN ORDER HARMONICS. Like the process used on Aphex Exciters but carried even further?IF not then any ideas on its development would be cool!

[dirk]

You can create even harmonic distortion with ringmodulators and 2 mixers.

This is how it works:
Put 2 sines into a ringmodulator and the output frequency will be the sum and the difference of the sines. If the 2 sines are the same frequency, than the output of the ringmodulator will be 0Hz and twice the original frequency.
So what you do is to put the signal you want to distort into both inputs of a ringmodulator and you get 2th harmonics.
To get 4th, 6th etc... you feedback the output of the ringmodulator back into the input with a mixer before the input. If you put a mixer behind the ringmodulator and mix it with the original signal you have total control over the amount and contend of the even order distortion.

[Krunchy2]

That sounds interesting but wouldnt it only generate octaves? The exciter process  is much broader in its spectrum and works like a shelving eq across the harmonic series(somehow filtering the dissonant odd-order tones). I was looking for a full bandwidth solution which would dial out the original signal leaving the distortion (which would have to be very sweet!)

[dirk]

That sounds interesting but wouldn't it only generate octaves?

Thats what even order harmonics are.
Of cause this circuit produces for every harmonic in the signal a series of even harmonic overtones.

The exciter process  is much broader in its spectrum and works like a shelving eq across the harmonic series(somehow filtering the dissonant odd-order tones).

With the circuit mentioned you can dial in the level of the second harmonic and the level of the 4th, 6th, 8th etc... More ringmodulators and mixers would allow you to mix the 8th harmonic higher in level than the 6th for example.

I was looking for a full bandwidth solution which would dial out the original signal leaving the distortion (which would have to be very sweet!)

Just turn down the level of the original signal.

I'll see if I can make an example of this circuit with my Clavia micro modular.

[dirk]

Here can you find a picture of the circuit and a soundfile: http://www.sendspace.com/file/wxxhyl
I used a TB-303 into the input of the Clavia, the output of the Clavia into the recorder. This circuit only produces even harmonics (and a bit of aliasing, because its digital) so it sounds quite different than normal distortion.
First you hear the direct sound, folowed by some knob tweeking. As you can hear it can be quite drastic, but also quite subtle.

I leave it up to others to make this into a stompbox.

[caress]

ahh man i love the micro modular... wish i had one   

[soggybag]

There is a schematic for a Ringmod type device that does something similar to what you are describing at viva analog.

http://www.lynx.bc.ca/~jc/pedalsHarmonic.html

[snap]

How about an octaver?

[dirk]

There is a schematic for a Ringmod type device that does something similar to what you are describing at viva analog.

http://www.lynx.bc.ca/~jc/pedalsHarmonic.html

This thing only produces 2th harmonics. With a mixer at the input and feedbacking the output of the ringmodulator, you can create more even harmonics. See my description earlier. To achieve this, add a pot and a resistors to the schematic.

[Krunchy2]

THX for ideas but theres a couple problems . First the even -order partials are not just octaves -they are the intervals octave,fifth,fourth,major and minor thirds and their octaves etc.. All tones generate even and odd partials-just in varying degrees of amplitude.The even partials are less dissonant and boosting them is appealing to humans.Boosting odd partials fools us into thinking its  out of tune or somethings not quite right.Traditional fuzz effect boosts even and odd partials and the solution in the past was to try and eq it somehow to reduce the odd partials(not with much results from my view).

[dirk]

THX for ideas but theres a couple problems . First the even -order partials are not just octaves -they are the intervals octave,fifth,fourth,major and minor thirds and their octaves etc..

This is not a problem, I was wrong in saying even harmonics are octaves. The circuit mentioned can produce all even harmonics including 5th, Maj3th, 4th etc... (of cause limited by the bandwith of the circuit). It of cause can't produce, for C1 as 1st harmonic, Es1, E1, F1, G1, but that must be evident.

Symmetric distortion produces uneven harmonics, asymmetric distortion produces uneven and even harmonics.

Edit: Uneven harmonics seem to put the sound more forward (in your face sound) and even harmonics seem to put the sound more backward (give air to the sound) in the soundfield.

[slideman82]

Hey, you'll have to limit the superior order harmonics... beyond 7th, it's not musical! Even 6th sounds quite bad!

Just build a tube amp! 

[SeanCostello]

I might be wrong, but I thought that a full-wave rectifier only produced even harmonics. And it pretty much defines the octave-up sound.

The Aphex Aural Exciter uses a one-sided clipping (i.e. one side of the waveform is limited to a certain threshold, while the other side has no limitations). This will produce both even and odd harmonics.

Sean Costello

[Eb7+9]

There is a schematic for a Ringmod type device that does something similar to what you are describing at viva analog.

http://www.lynx.bc.ca/~jc/pedalsHarmonic.html

This thing only produces 2th harmonics. With a mixer at the input and feedbacking the output of the ringmodulator, you can create more even harmonics. See my description earlier. To achieve this, add a pot and a resistors to the schematic.

we have had many "messy" arguments about this - thanks mainly to the limitations of ascii communication and time to properly express our understanding ... a multiplier will not produce a pure octave when hit by a non-pure waveform, what comes out of a string instrument ... what the HarmonicMultiplier puts out is principally a second harmonic (octave) and a bunch of side terms depending on how impure the waveform is (there is no way around that unless you go artificial-digital reconstruction) why some people like to roll off the treble on their signal before hitting an analogue octaver circuit ...

having said that a multiplier will in general produce a cleaner second harmonic on a  pure single tone than other types of "squaring" circuits ... my circuit ends up sounding like a dry Bassman "sort-of" when the mixer is set between 5-20% wet to dry mixing - but mine's not an easy build and the nulling also requires work to get right ... there are simpler pre-nulled multiplying chips (AD533 ?? I forget) that you can pair to a linear mixer to achieve a similar result ... the circuit is a neat tool to have when doing doubled parts on a recording, adding a pleasing difference to a basic sound ...

best ...

[mac]

Harmonic Percolator IIRC

mac

[dirk]

There is a schematic for a Ringmod type device that does something similar to what you are describing at viva analog.

http://www.lynx.bc.ca/~jc/pedalsHarmonic.html

This thing only produces 2th harmonics. With a mixer at the input and feedbacking the output of the ringmodulator, you can create more even harmonics. See my description earlier. To achieve this, add a pot and a resistors to the schematic.

we have had many "messy" arguments about this - thanks mainly to the limitations of ascii communication and time to properly express our understanding ... a multiplier will not produce a pure octave when hit by a non-pure waveform, what comes out of a string instrument ... what the HarmonicMultiplier puts out is principally a second harmonic (octave) and a bunch of side terms depending on how impure the waveform is (there is no way around that unless you go artificial-digital reconstruction) why some people like to roll off the treble on their signal before hitting an analogue octaver circuit ...

I would really like to hear these arguments.
As I understand it every signal is made up from sines (Fourier) and therefore multiplication of a signal with itself will produce for every harmonic in the original signal an octave of that harmonic.

[Mark Hammer]

Actually, one of the Aphex Exciters (I forget which model) used this exact approach, feeding in a copy of the input signal to one half of an LM13600, and a second copy to a high-pass filter which then fed the Iabc pin of the 13600.  In other words the modulation of the original signal by a copy of itself was restricted to mid-harmonics and above such that one would get doubling and augmentation of harmonic content but not added lower-order harmonics from the fundamental.

[SeanCostello]

Actually, one of the Aphex Exciters (I forget which model) used this exact approach, feeding in a copy of the input signal to one half of an LM13600, and a second copy to a high-pass filter which then fed the Iabc pin of the 13600.  In other words the modulation of the original signal by a copy of itself was restricted to mid-harmonics and above such that one would get doubling and augmentation of harmonic content but not added lower-order harmonics from the fundamental.

This would also act as a "transient exciter," as you are squaring not only the harmonics, but also the amplitude envelope of the signal, which results in a much faster decay.

Sean Costello

[Mark Hammer]

Which is precisely the desired result.

[SeanCostello]

Which is precisely the desired result.

I guess. When I have programmed "harmonic enhancers" (the Aphex patent has lapsed, but the Aural Exciter name is still a trademark), I found that the asymmetric clipping sounded much better than squaring the input signal. You would hear much more "sheen" on cymbals, and no weird staccato transients.

I know that some bass boost algorithms square up the low-frequency filtered signal, but precede the squaring with a compressor, to undo the squaring of the amplitude envelope. A full wave rectifier is nice in that it preserves the signal envelope, but the even order harmonics produce too much of an octave artifact, which is not what you want for psychoacoustic bass boost.

Sean Costello