thanks florian!!
synthfreak






--- In Doepfer_a100@y..., Florian Anwander <Florian.Anwander@c...>
wrote:

> Hi Bakis
>
> > dieter doepfer: "[...]Maybe someone
> > of the newsgroup knows detailes too (Florian ).[...]
>
> The "comb filter" thing I already mentioned in the mail from 4th of
> February. I wrote
> "[...]by an allpass filter (which is used also for phaser) or by a

delay.

> Both do similar but technically not identical effects."
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> I thought this was very clever, since I had not to explain the

difference

> in detail ;-) ok, now you've got me...
>
> The difference between the (analogue) phaser and the flanger in

reality is

> the technical way, how a signal delay is created.
>
> The delay in the flanger is realized with some kind of signal

storage,

> which does not change the signal itself generally. The stored

signal is

> kept for a while and then played back. This is realized either with

digital

> storage or in older flangers and guitar efx with so called bucket

bridge

> delays.
>
> The phase works also with a delay, but this time the delay is

realized with

> an so called allpass filter. An allpass filter is a circuit which

does

> not(!) filter. This sounds senseless as long as you think filtering

is the

> only thing that a filter does; but a filter does a lot more:
> - it does a very(!) small delay (this is, what the phaser wants to

use)

> - and it shifts the phase of partial notes above the cutoff-

frequency

> (yes an allpass filter has still something like a cutoff-

frequency,

> though it does not cutoff anything). This phaseshift is

originally

> not intended, but it is typical for all analogue filter designs.
>
>
> As we already learned: A comb effect is generated by elimination of

partial

> tones, which happen when a delayed signal is mixed together with

the non

> delayed signal. Now you can imagine, that the phase shift of the

partial

> tones in the allpass will cause, that other partials will be

eliminated.

>
> So far the technical background.
>
>
> __Which__ special frequencies are eliminated and how this looks

(linear or

> logarithmic...) I do not remember. Sorry. I know there is a paper

somewhere

> deep in the big paper sink in my room ;-) but I cannot promise,

that I will

> find it. So I fear the answer won't be better than the one, you

already

> received by Dieter.
>
> Florian
>
>
>
> --
> Florian Anwander |ConSol* HP-Support
> Tel. +49.89.45841-133 |Consulting&Solutions Software

GmbH

> Fax +49.89.45841-139 |Franziskanerstr. 38, D-81669

München

> email: florian.anwander@c... | http://www.consol.de