[sdiy] freq shift allp filter ?

Mon Jan 13 23:02:29 CET 2003

Juergen Haible has a design on his site under the
Frequency Shifter schematics...

its also known as a 'dome filter'.

There is more info in Electronotes (somewhere....)

EDN or Electronic Design magazine had a(n) Design Idea or
Ideas for Design on this subject as well.

The phase difference is 90 degrees between the two filter
sections... but might be many hundreds of degrees overall....
(the absolute phase is NOT constant... only the difference)

H^) harry

--------Original Message--------  

From: fdi at ran.es
To: synth-diy at dropmix.xs4all.nl
Sent: Jan 13 2003 20:52
Subject: [sdiy] freq shift allp filter ?

>
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>     Hi all, and happy new year.
>     I'd like to build a frequency shifter (phase type) made out of various modules (quadrature
>     osc, 90deg allpass filter and two ring mods), better than a large circuit.
>     I'm not looking for linearity or precision, just one more musical tool within my modular
>     syntheziser.
>     I have the two ring modulators (Roman Sowa design, AD633 based) and I see there are some
>     quadrature oscilators on the net (some simpler than others). But I have many questions
>     about the filter...
>     At first, I thought that using a cell from a phaser would just yield the 90 degrees
>     shifted signal, but I readed that it will not shift the same amount for all freqs... Then
>     I understood that what I need is a short delay to shift the signal 1/4 of it's period, so
>     a delay capable of very short delay times was the solution... but, as far as I can
>     imagine, this will only work for one frequency...
>     So, dear masters, what kind of "90deg constant phase shift filter" is needed for this kind
>     of freq shifting?
>     And, very important (I'm not an EE), there is any circuit ready to build out there?
>     (for those not familiar (ough! am I?) the circuit I'm talking about: input signal to
>     filter / filter 0deg out to RMa / filter 90deg out to RMb / QOSC sin out to RMa / QOSC cos
>     out to RMb / RMa and RMb out are the up and down shifted signals, QOSC freq is the shift
>     amount)
>     Thank you for your time and patience,
>     Fernando
>     f
>     *
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