[sdiy] an old serge UI secret and a primordial question

[harrybissell at copper.net]

One phase shifter stage can shift 90 degrees
at a single frequency.

Getting "all" frequencies shifted requires
a bunch of cascaded stages. The dome filter
has a phase difference of 90 degrees, but overall
the shift is in the thousancds of degrees.

The lower the frequency you want the filter
to work at, the more stages you need and the
longer the total delay is as you go through the
filter. This could be in the tens of milliseconds
range.

I wanted to frequency shift a guitar up, and detect the
pitch faster. Trouble was the dome filter introduced
the same delay I'd get from the fundamental itself,
or worse. 

There is no free lunch...  :^P

H^) harry




>
>
>
>---- Original Message ----
>From: jmahoney at gate.net
>To: abisset at dspaudio.com, synth-diy at dropmix.xs4all.nl
>Subject: Re: [sdiy] an old serge UI secret and a primordial question 
>Date: Wed, 18 Apr 2007 10:40:05 -0400
>
>>At 06:57 AM 4/18/2007, Anthony Bisset wrote:
>>
>>>...  So, having 2 outputs makes
>>>sense for a live performance system.
>>
>>Or, you can make sure that the plug that will need to be removed is 
>>plugged in last, so that you can remove it without disturbing the
>others.
>>
>>
>>>...  90 degress seems optimal, so just an opamp would do the trick,
>>
>>Well, a 180 degree phase change (actually polarity inversion) is 
>>trivial with one op amp. 90 degrees is not quite so trivial, as far
>as I know.
>>
>>Phase shifters ("phasers") use a number of all pass filters to, uh, 
>>shift the phase. So I guess I'm saying that you should study some 
>>phase shifters. (Ray Wilson and others sell phaser PC boards, maybe 
>>you could modify one for your purposes.)
>>
>>Also, check out the IBP Analog Phase Alignment Tool (and Junior)
>from 
>>Little Labs:
>>         http://www.littlelabs.com/ibp.html
>>         http://www.littlelabs.com/ibpjr.html
>>--
>>john
>>
>>
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