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Phase rotation in both directions?


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#1 ffx

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Posted 15 May 2018 - 20:31

Hi,

 

do you know a vst or a native way in Renoise how to rotate the phase in both directions? The "width" slider and the stereo tool seem to rotate only to the right, to a maximum of 180 degree. Or am I wrong?

 

Would left rotation introduce pdc then?

 

Thanks.


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#2 Zer0 Fly

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Posted 15 May 2018 - 20:55

https://www.meldapro.../MFreeformPhase

 

like this? it is like an allpass eq from what I see...

 

there are different ways to manipulate phase, phase shift is brought by delays - or filters, so analog/iir or digital/fir. standard allpass filter would be iir following a certain curve, traditionally used to get bass from multi mic recordings in phase again. the melda thing is probably a fir design, allowing arbitrary curves, and yup...phase shift is mostly like delaying individual frequencies of a sound differently, so shifting a frequency ahead (or rather delaying everything else...) with fir filters will need to introduce negative delays thus pdc...just like those linear phase eqs that will use fir filters to implement frequency manipulation without phase shift.

 

the width is different I think, more like a mid/side technique. the renoise surround thing seems to do phase shifting of l/r seperately, as in full effect a mono sound is totally out of phase over the whole spectrum.


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#3 ffx

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Posted 15 May 2018 - 21:30

Thanks! Nice plugin. I think the melda thing is based on FFT, is that possible? Panning each band then?

 

I really think the width slider does exactly what the "surround" slider of the stereo expander does: Phase rotation. Maybe one could prove or prove the opposite?

 

But I think I found A tool which actually does "traditional" phase rotation to the left: Voxengo PHA 979

pha979-large1024.jpg


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#4 Zer0 Fly

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Posted 16 May 2018 - 18:14

yes, probably based on fft/digital filter/fir...digital filters are often implemented with fft processing, but not direct fft manipulation... with fir filters you can basically design filters with arbitrary freq/phase responses, within certain limits (length of the filter kernel, steepness of filter graph slopes, pre/post ringing, possible pdc induction....)

 

and you are right, the track mixer width slider seems to do exactly the same as the "surround" slider on the stereo expander. I mixed it up with the "expand" slider in it, which will use m/s mixing to manipulate sounds. testing with sine waves, you will see the width/surround indeed will sucessively put signals out of phase when engaged...you are probably right about the phase rotation that is dealing the same phase shift around the whole frequency spectrum, from 0° to 180°...to get more info on this, one could sample impulses through the devices and analyse the phase responses with some math software...

 

I dislike using the surround/width sliders by the way and try to not use them on regular basis, they can bring strange problems in the mix...like messing up mono compatibility, which I think is important to get a consistent sound on stereo systems too...sounds with such phase shifting will cancel itself if l/r are clashing in some way... also they mess the very high frequencies...

 

it is sometimes very tempting, to deal the surround/width on just the wet reverb, to push it into the background...when mixed mono, the reverb will partially disappear depending on the out of phaseness dealt to it, which could be actually desireable for gaining clarity in situations where stereo isn't working ideally...at least I think it could...


Edited by Zer0 Fly, 16 May 2018 - 18:16.

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