Hello Brian,
> The omni was either hard wired in an antiphase fashion or recorded as
> a second channel and later applied during post recording editing.
> From what I gather, everyone seems to have abandoned the experiments
> due to an increased perceived noise floor speculated to be due to
> spatial "time of arrival" (phase) issues.
I have a microphone mount on the rear of the parabolic dish I made. I
record both forward and reverse sounds on separate channels, pointing
the rear mic towards the source of the loudest unwanted sound. By
digitally inverting the phase of the rear one and mixing it with the
original signal, I nearly cancel the unwanted one. This is a fairly
standard means to achieve this and I've found that "time of arrival"
phasing problems are only an issue with high frequencies. Since high
frequencies are quite directional then this isn't going to be a problem
with the rear-facing mic behind my parabolic reflector unless there is
a very reflective surface behind it.
Your idea of collecting samples of unwanted noise is precisely what
most Digital Signal Processors (DSPs) for audio work do. I can't say
I've tried it yet but you would have to make sure that your "looped"
sample was long enough so that the listener couldn't detect any pattern
in the noise-cancellation and that the sample accurately represented
the unwanted sound, otherwise it will just add to the general
background noise that you are trying to eliminate. Although this
method is great for eliminating line hiss on the overseas telephone
networks, the range of sounds when recording outside may be too diverse
to allow this to happen. Great idea Brian, I'm really curious to try
your method!
I tend to shy away from recordings where background noises have been
artificially reduced but this is just my choice. Yes, I want clarity,
but the rustling of grass and leaves in trees or water in a creek bed
really puts the sound I'm recording into context. This is quite
subjective and I'm sure everyone has their own preferences, especially
if the recording is to used to identify wildlife.
Cheers,
David.
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