Phasers, HELP PLEASE

iPassenger · Posted: Fri Jan 27, 2012 2:24 am Post subject: Phasers, HELP PLEASE

Last night I spent a good few hours trying to recreate the sound of the Phaser from the FX section using either the Phaser Filter, a phasor constructed from the State Vairable filter in allpass mode and manually constructed all pass filters.

My results were pretty disappointing.

Phaser filter:

I got the closest with this but there is a smooth smearing of the sounds present in the one from the FX block (on setting II) that I can't seem to get right, no matter what I set things too or how I sweep the filter. Even tried sweeping the spread as well a bit to see if that was somehow related. But I think the difference is in the way the filter is actually filtering or perhaps has something to do with how the feedback is implemented.

All Pass Filter from SVF:

This was terrible in the main, i can get things that sound phasey but its just not the same.. Either I am not making them right or the all pass filter in the SVF (band pass output on 6dB) mode isn't right at all. Any thoughts?

Home brew All pass filter (made from the low pass modules):

Again it's just not right, can anyone help me to understand exactly how a proper all pass filter with feedback should be constructed? And how several of these should be arranged in order to make a phaser.

I would really love to make my own phaser that sounded as good as the one in the FX section (or better perhaps) but it just isn't happening, can anyone help?

Cheers in advance

Ross

Roland Kuit · Posted: Fri Jan 27, 2012 5:27 am Post subject:

I pm-d you.

iPassenger · Posted: Thu Feb 02, 2012 4:09 am Post subject:

Roland and I have spent quite some time messing with these but were still not getting the smeared filtered sound that the Phaser FX on setting II produces. He has however provided some pretty cool effects as a taster of his SLII.

Anyone else got any ideas they would like to share? Or is it just not really possible?

Alternatively can anyone explain to me the typical wiring of an analog phaser and maybe then I can work on that basis? I know it has something to do with all pass filters... But I am not sure how they are arranged (series, parrallel, how does the feedback work etc etc..)

When I create these (All pass filters) manually in the nord everything above the cut off frequency ends up 180 out of phase and everything below is in phase, with points around the cutoff at various points in between. Is this the right behaviour? How many poles should the all pass filter have (more or less)?

Cheers

Ross

Roland Kuit · Posted: Thu Feb 02, 2012 12:10 pm Post subject:

This 1 comes far. Implemented I and II:

Roland Kuit 2+1 Phase I&II test.jpg

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Roland Kuit · Posted: Thu Feb 02, 2012 3:56 pm Post subject:

You can replace the 2 Notch phaser with 2 DelaySingle B modules. Tomorrow I'll post a pic.

ian-s · Posted: Thu Feb 02, 2012 6:50 pm Post subject:

Here is something else to play with though I can't seem to tweak it to match. It uses Rob's allpass sections from his 'massive phaser' patch.

Looking at the spectrum of the FX version, seems to be just 4 or 6 stages for the Type I and Type II.

So you can use any of the phase filter, 6dB multi mode, or Robs. You get 1 notch per pair of allpass sections.

There is another type of allpass based on a delay line but it is a different animal. Used in reverb stuff.

The difference in character is there before feedback it seems to me.

The classic phaser is just cascaded allpass signal mixed with the input. A 50:50 ratio gives the deepest notch.

diy_phaser.pch2

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diy_phaser.pch2

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iPassenger · Posted: Fri Feb 03, 2012 2:00 am Post subject:

Thanks folks, plenty to chew on here. Smile

iPassenger · Posted: Fri Feb 03, 2012 2:12 am Post subject:

Roland Kuit · Posted: Fri Feb 03, 2012 2:39 am Post subject:

Nice Ian. I know this cascading filter trick. Here the pic as promished.
I had send Ross a pch op-amp filters-phaser. Just to experiment for fun.
Wicked.

Roland Kuit Comb I&II 2A.jpg

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ian-s · Posted: Fri Feb 03, 2012 12:51 pm Post subject:

iPassenger · Posted: Tue Feb 07, 2012 2:28 am Post subject:

Thanks for posting these I did have a quick play with them and managed to get pretty close. I've not had a thorough mess building my own yet though as i have been busy with another project.

I think the stack of the two filter/mixer arrangements (in series), combined with the feedback signal containing a mixture of the input and output was what I was missing.

Smile