For anyone that wondered what was that guy taking about re: "phase
invert noise cancellation". Here is an example:
The sound file is a porcupine in a dead run to get to a tree. Yup,
that means he was going about 2 miles per hour and still taking rest
breaks. He is running through very dry brushland that is currently
under an extreme fire hazard due to high winds with dry land. I use
this an example not because it is the impressive example file but
rather because it is broad freq sound and you can more easily hear
what the dish does and what the noise cancellation does.
Recorded using parabolic dish (this one 32") with two omni microphones
spaced at 1.5" apart with no barrier.
As a stereo file it sounds like this 800kb download.
http://home.comcast.net/~richpeet/porkystereo.mp3
Now I take one of the channels and invert the channel so that all the
positive voltage peaks of the sound are now negative, and the negative
voltage peaks are positive. I then sum the two stereo channels into a
mono file mixing the two channels equally into one. I bring the gain
up as needed to match the stereo file.
The result is that any sound that was identical between the two
microphones in the stereo file is cancelled out and goes away.
As a noise cancelled mono file porky sounds like this 400kb download.
http://home.comcast.net/~richpeet/porkymono.mp3
No other edits done than as discribed. Clearly not something you will
always use but it is a tool with its uses.
Rich Peet
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