cable length needed to create phase shift?
"Michael R. Kesti" wrote in message
Ben Bradley wrote:
snip
What could be a real problem with 1000 feet of cable is high
frequency rolloff due to the capacitance of the cable.
Hmmm... Everybody's been discussing the propogation delay aspect of
the question, but the phase shift introduced by the RC filter that
results in that HF rolloff is far more significant. At frequencies
less than 1/10th that filter's corner frequency, the frequency at
which 6 dB of loss occurs, the phase shift is negligible. The shift
is 45 degrees at the corner frequency and grows to nearly 90 degrees
at frequencies about 10 times the corner frequency.
Depending on the signal's source impedance and the cable's
capacitance, then, relatively short cables can result in appreciable
phase shift.
Yes, but there are frequency response losses associated with delay obtained
this way. Most people who say they are looking for phase shift are looking
for phase shift without frequency response losses. If moderate amounts of
delay are desired, all-pass networks can be a solution for this requirement.
If more delay is desired, then digital delays can be good and priced
reasonably. However, all such delay must be causal - IOW the delay has a
positive amount of time associated with it.
In a DAW environment practically arbitrary amounts of what, from the
viewpoint of the recording amounts to be causal or acausal delay are
basically *free*.
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