Hi Igor,
PDN is "phase difference network". It's a circuit used inside a
frequency shifter to create two versions of the input signal which will
have a 90 degree relative phase difference between each other over a
wide frequency range.
Frequency shifters need a sine and cosine version of both the input
signal and the carrier signal in order to operate. The sine versions of
signal and carrier are put through one ring modulator, and the cosine
versions are put through another ring mod. Then they add (or subtract)
the two ring mod outputs together to get the final output.
In the case of the Serge external carrier shifter, an extra PDN would be
needed to take the external carrier input and make sine and cosine
versions of it. In the internal version, the built-in carrier
oscillator comes with sine and cosine outputs (it's a quadrature
oscillator), so the extra PDN isn't needed. I assume that's how the
Serge shifters work anyway, I've never peeked inside one.
I haven't heard of anyone making a PDN module for a modular synth
system, but if there was one, you could probably patch up your own
frequency shifter manually using a PDN, two ring mods, a quadrature
oscillator and a mixer.
-Chris
dahlia13@... wrote:
PDN is "phase difference network". It's a circuit used inside a
frequency shifter to create two versions of the input signal which will
have a 90 degree relative phase difference between each other over a
wide frequency range.
Frequency shifters need a sine and cosine version of both the input
signal and the carrier signal in order to operate. The sine versions of
signal and carrier are put through one ring modulator, and the cosine
versions are put through another ring mod. Then they add (or subtract)
the two ring mod outputs together to get the final output.
In the case of the Serge external carrier shifter, an extra PDN would be
needed to take the external carrier input and make sine and cosine
versions of it. In the internal version, the built-in carrier
oscillator comes with sine and cosine outputs (it's a quadrature
oscillator), so the extra PDN isn't needed. I assume that's how the
Serge shifters work anyway, I've never peeked inside one.
I haven't heard of anyone making a PDN module for a modular synth
system, but if there was one, you could probably patch up your own
frequency shifter manually using a PDN, two ring mods, a quadrature
oscillator and a mixer.
-Chris
dahlia13@... wrote:
>
> >
> > One thing I always wondered about the external carrier
> > version is the lowest possible frequency shift.
> > PDNs have a lower corner frequency by definition. The
>
> Excuse my ignorance, but what does PDN stand for?
>
> Igor.
>
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