Re: New York - ISSUE Project Room 23rd & 28th of April

[andy butler <akbutler@tiscali.co.uk>]

On 20/04/2014 23:02, Stefan Tiedje wrote:

> well, hilbert transformation isn't really frequency shifting...;-)
> I don't know of any hardware device which does it, but maybe I'm wrong...

The Hilbert Transform is used as part of the Bode Frequency shifter.
It's a 90 degree phase shift allpass filter, so on it's own
it won't really do anything audible.

Really the Bode is a kind of super version of a ring modulator.
Instead of 2 side bands being generated for each frequency input
you just get one, either up or down.
i.e. just the sum, or the difference tone, not both.

So it's almost like a pitch shifter, except that rather than shifting the
pitch by a fixed amount it shifts the frquency by a constant.

So, as the sound is shifted it's harmonic structure gets all dissonant.

Bode Frequency shifters are rare, because it's hard to achieve
the Hilbert Transform in hardware. I think there's something available
in the modular synth world.

In stomp box land the Electro Harmonix Ring thing has an excellent
digital(unless I'm wrong) implementation of the Bode,
called "Single Sideband Modulator".

Have a great gig!

andy