posted 07 November 2002 06:50            

I don’t know if this has been done before?

All distortion units seem to have one thing in common weather they are a
fuss box ,exciter, valve emulator, overdrive unit etc. That is that the
extra harmonics added, vary dependent on the level of the input signal.
What I have constructed here is a Phase Distortion system where by the harmonics
that are added to a wave form will be in the same proportion and type,
regardless of the signals input level.

This is how it works

First we put our signal into the 90 deg phase shifter and make a real
and imaginary wave form.
Then if we put these through the RMS module, we get a signal that
represents the distance from 0,0 (if we think of it as a 2D picture).
We then use the real and imaginary signals to generate a Phase angle
signal.
Using just these two new signals (distance and Phase angle) we can
manipulate them (using sine and cos etc) to get back the original
signal.

Big deal so we've made a unit that does nothing.

But the important point here is that the Phase angle signal will be the
same for any given input wave form that has the same shape, regardless of its
level. i.e. if we put an attenuator on the input, the
Phase angle signal would be exactly the same shape and size as if we
hadn't put the attenuator there.

Therefore if we were to put the Phase angle signal through a wave shaper
before decoding it back to the original signal we would get non level
dependent distortion.

That's the theory but a lot of corners can be cut in the attached real
implementation.

Instead of finding the Phase angle signal I make two wave forms
that are phase indexes.
I make these by getting the real wave form divided by the distance wave
form, and the imaginary divided by the distance.

These two signals have a special property . When they are put into
the RMS module they always produce a DC signal of level one. Also these
two signals don't change by putting an attenuator on the input.
And also the original real and imaginary signals can be retrieved by simply multiplying them by the distance wave form.

So if we put one or both of these phase index signals through a wave shaper before multiplying it by the distance wave form we get a similar (but not quite the same) effect as above(distorting the phase signal).

Of cause in many cases we want to distortion to increase as the level rises , so this would be no good in these cases but if it were used as the distortion part of an exciter where we want to add a controled amount of harmonics weather the sound is loud or not , this should be ideal. It does of cause still have interharmonic distortion so richer sounds will still get a larger proportion of distortion than simple nonpoly sounds but it’s still a big step in the right direction.

If anyone makes an exciter using this phase distortion I would love a copy.

Note: there are some extra controls on the VCS for experimenting with and manipulating the distance waveform, so to hear the true phase distortion only ,these controls and the "Double" control must be set to zero.

If any ones interested, when the Double control is set to one,the unit remaps the phase so that it rotates 720 degs for 360 degs rotation at the input. This makes the loudest sine in the input signal double in pitch but introduces so much distortion that it doesn’t sound any thing special. If you did put a simple sine wave in the input, it would come out at twice the frequency, and without the DC offset that you would get by simple ringmodulating a sine wave by itself.

Have fun

Pete

posted 08 November 2002 03:54            

Could you repost?

Thanks!

posted 08 November 2002 09:15            

PDU.kym

sorry