Doepfer

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
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