phasing, notches, dry, n'stuff

[Danich_ivanov]

I've seen electrosmash analysis of the phase 90 with dry signal hooked up (as it is basically), but i'm curious as to what it would look like without dry signal, how does it differ in terms of notches and phase shifting? And i'm not talking about phase 90 in particular, but anything similar where you can see the difference. If you have knowledge or graphs, that's what i'm looking for.

Thanks.

[DrAlx]

If there's no feedback of any sort in the phase-shifted path, then then you need dry signal to give you notches.

Graphs: See http://1drv.ms/1flKf0d.

e.g. for a 6 stage phaser with identical all-pass stages with no feedback.

https://www.wolframalpha.com/input/?i=plot+abs(1%2BP)+where+P%3D((pi*ix-6)%2F(+pi*ix%2B6))%5E6+from+x%3D0+to+10

For 4 stage phase, replace all the 6's in the formula box by 4.  etc, etc

[Danich_ivanov]

If there's no feedback of any sort in the phase-shifted path, then then you need dry signal to give you notches.

Graphs: See http://1drv.ms/1flKf0d.

e.g. for a 6 stage phaser with identical all-pass stages with no feedback.

https://www.wolframalpha.com/input/?i=plot+abs(1%2BP)+where+P%3D((pi*ix-6)%2F(+pi*ix%2B6))%5E6+from+x%3D0+to+10

For 4 stage phase, replace all the 6's in the formula box by 4.  etc, etc

Unfortunately none of these load on my phone. So what you're saying is that dry signal is required to create notches, otherwise there will only be 720° degrees shifting (considering 4 stages), with minor frequency changes (as there is still some filtering happening)?

[antonis]

What Alex said..

Without dry signal, all you have is a "clean" all-pass filter..
There isn't anything to be summed on out of phase (delayed) wet signal, hence no cancellation may occur..

P.S.
An intertersting reference:
Bartlett, B., "A Scientific Explanation of Phasing
(Flanging)," Jour. Aud. Eng. Soc., vol. 18, no. 6,
December 1970, pp. 674-675.

[Danich_ivanov]

What Alex said..

Without dry signal, all you have is a "clean" all-pass filter..
There isn't anything to be summed on out of phase (delayed) wet signal, hence no cancellation may occur..

P.S.
An intertersting reference:
Bartlett, B., "A Scientific Explanation of Phasing
(Flanging)," Jour. Aud. Eng. Soc., vol. 18, no. 6,
December 1970, pp. 674-675.

I see. And that's pretty much what i expected, just thought there is something else going on. I'll check the read, thanks.

[antonis]

Just to make it more clear..

Without dry signal, up right summer is effectively turned into output inverting buffer (with gain, in current configuration)..
(there isn't anything to be added on phase shifted signal so OUT is an inverting replica of whatever comes from DEPTH pot's wiper..)

[Mark Hammer]

With no dry signal combined and NO feedback within the phase-shift section of the circuit, the allpass stages create modest pitch shift.  However, when feedback is introduced, one does hear enhanced peaks as the LFO sweeps.  So I'm assuming that any audible resonant peaks implies some dips between them.

[ElectricDruid]

With no dry signal combined and NO feedback within the phase-shift section of the circuit, the allpass stages create modest pitch shift.

Isn't that only true when the all pass stages are modulated? A *changing* phase shift is a frequency, but a fixed phase shift is just that - fixed. If you took the dry path out and had good quality static all pass stages, you shouldn't really hear them. After all, clue's in the the name: "all pass" - they pass everything, no frequency effects at all, only phase effects.

[Mark Hammer]

Yes.  Completely correct, and I should have not assumed that little detail would be assumed.

[Danich_ivanov]

With no dry signal combined and NO feedback within the phase-shift section of the circuit, the allpass stages create modest pitch shift.

Isn't that only true when the all pass stages are modulated? A *changing* phase shift is a frequency, but a fixed phase shift is just that - fixed. If you took the dry path out and had good quality static all pass stages, you shouldn't really hear them. After all, clue's in the the name: "all pass" - they pass everything, no frequency effects at all, only phase effects.

But isn't it where the genious of a phaser effect comes in with a smaller caps (or shall i say a carefully choosen ones) that allows for a slight frequency shifts, besides purely changing the phase?