[Scott Dorsey]

William Sommerwerck wrote:
You need two all-pass filters. One produces a phase shift of phi. The other
producers phi+90 or phi-90.

It is impossible to produce a fixed 90 degree phase shift over a wide
frequency range and have flat response at the same time. You have to create
the 90-degree shift as the difference between two filters' phase responses.

Yes. This is also discussed in Tremaine's Audio Cyclopedia which is the
first reference I recommended in this thread.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."