Login / Register 0 items | $0.00 New @ KVR
User avatar
Smashed Transistors
KVRist
 
126 posts since 10 Oct, 2014

Postby Smashed Transistors; Mon Feb 26, 2018 3:33 pm Re: FM synths - Anti-aliasing/Oversampling

Integration/derivation also induce phase changes.
They are not critical with sine waves and considering the f scaling is enough.

I think that phase matters very much with complex waveforms as modulators.

For example, using a sawtooth as a modulator leads to something that is similar to osc sync sweeps. If you use a waveform with a similar spectrum as the sawtooth but with different harmonic phases, the result is much different.
See you here and there... Youtube, Google Play, SoundCloud...
mystran
KVRAF
 
4888 posts since 11 Feb, 2006, from Helsinki, Finland

Postby mystran; Mon Feb 26, 2018 4:53 pm Re: FM synths - Anti-aliasing/Oversampling

Smashed Transistors wrote:Integration/derivation also induce phase changes.
They are not critical with sine waves and considering the f scaling is enough.


Well, right.. so multiply (or divide) the spectrum with i/f instead. :P
Image <- plugins | forum
User avatar
S0lo
KVRian
 
551 posts since 31 Dec, 2008

Postby S0lo; Tue Feb 27, 2018 10:16 am Re: FM synths - Anti-aliasing/Oversampling

Another thing that can cause severe aliasing is feedback modulation. That is, OP1 modulating OP2, then OP2 modulating OP1. This can very quickly go too wild and end up producing just useless noise. I personally prevent this by limiting the modulation amount in one direction and allowing it to be large in the other direction. But someone else may have better ideas :idea:
User avatar
Smashed Transistors
KVRist
 
126 posts since 10 Oct, 2014

Postby Smashed Transistors; Tue Feb 27, 2018 10:57 am Re: FM synths - Anti-aliasing/Oversampling

The feedback aliasing problem is sometimes called "hunting", it occurs even when there is only one oscillator when the feedback coefficient is big enough so that the system becomes chaotic with bifurcations.
To limit this effect you can use a simple "anti hunting" filter (as described in Yamaha's patent...) try to put a basic filter like y = 0.5f * (x + y) in the loop.
See you here and there... Youtube, Google Play, SoundCloud...
User avatar
S0lo
KVRian
 
551 posts since 31 Dec, 2008

Postby S0lo; Tue Feb 27, 2018 12:27 pm Re: FM synths - Anti-aliasing/Oversampling

Smashed Transistors wrote:The feedback aliasing problem is sometimes called "hunting", it occurs even when there is only one oscillator when the feedback coefficient is big enough so that the system becomes chaotic with bifurcations.
To limit this effect you can use a simple "anti hunting" filter (as described in Yamaha's patent...) try to put a basic filter like y = 0.5f * (x + y) in the loop.


hmmm, bit confused :? filtering an arbitrary wave (modulator) will obviously change it's shape. it's no longer THAT wave any more.

And if they're filtering sin waves!!! well, thats just equivalent to lowering it's amplitude, which is the same as lowering the modulation amount.

I haven't read the patent, so I'm probably missing something here.
User avatar
Smashed Transistors
KVRist
 
126 posts since 10 Oct, 2014

Postby Smashed Transistors; Wed Feb 28, 2018 12:30 pm Re: FM synths - Anti-aliasing/Oversampling

It only filters the high end of the spectrum.
As it is fed back, it is no more a sine wave.
For example, when you feed back one oscillator on itself, as you increase the feedback the sine morphs into sort of a sawtooth.
Without the filter, some HF ringing happens.
See you here and there... Youtube, Google Play, SoundCloud...
User avatar
S0lo
KVRian
 
551 posts since 31 Dec, 2008

Postby S0lo; Thu Mar 01, 2018 12:01 am Re: FM synths - Anti-aliasing/Oversampling

Smashed Transistors wrote:As it is fed back, it is no more a sine wave.


Your right. I don't know what I was thinking :dog:
Previous

Moderator: Moderators (Main)

Return to DSP and Plug-in Development