I would try to get some information on how this is done in the analog
world.  I used to know this 20 years ago :-|

There are applications for which you need a sine as well as a cosine
output over a fairly wide frequency range.  This easily done digitally,
but for an analog application you would want to use one sine wave
oscilator and than phase-shift the output 90 degrees. Older analog
implementations of surround sound implementations must have had similar
circuitry.  I would search for patents that describe those.

Job van Zuijlen

Anders Andersson wrote:
> 
> >> How can one easily do a 90 degree phase-shift on a signal?
> >>
> >You can't, unless you can describe all of the frequency components
> >exactly.  The closest you could probably get is to take an FFT and shift
> 
> Ok, so there are no easy way as it is with a 180° phaseshift?
> When encoding for dolby-surround, the "surround" signal has to
> be splitted and phaseshifted +90 and -90 degrees.
> I heard that it's not really ok to leave one and shift the other by 180°.
> 
> .--- -- -  -
> | Anders "Pipe/Nature" Andersson, pipe@algonet.se
> :

-- 
Arlington, VA, USA