[sdiy] phase shift

[mark s]

is it possible to design a circuit that can variably shift the phase of a 
(complex) input signal, while retaining the highest quality/integrity of 
the signal? by this i mean turning one pot that shfts the entire signal 
forward in time up to 180 (or more) degrees (or perhaps measured in tenths 
of a microsecond instead of degrees). would it be based on some kind of an 
all-pass filter, or some kind of delay circuit, or ??

mark