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Old February 24th, 2006, 08:51 PM   #1
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M/S 'decoding' in FCP?

Anyone know if it's possible to flip the phase of an audio channel in Final Cut Pro (or in Soundtrack Pro) so that I can set up audio from Cardioid & Fig 8 mics to create stereo from the M & S signals (M+S, M-S)..?
Has anyone tried this..?
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Old March 5th, 2006, 10:49 PM   #2
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I asked the same question a couple weeks ago myself. Matrixing in post makes a lot of sense. It's amazing to be able to zoom the mic in and reduce side noise during the edit.

You can do this conversion in Soundtrack Pro. It's a bit inconvenient, however. Alternatives are to use the Waves S1 VST plug-in from within Peak or Arboretum Systems Hyperprism plug-in from within Hypervision-AV. Arboretum plans an Audio Unit plug-in for FCP later this year.

If you do it yourself in STP, here's Sennheiser's description of the algorithm:

"If a matrix circuit is not available on the mixing
console, matrixing can be performed using the 3-fader
method (see diagram). The M signal is connected to
the first microphone channel and panned centre. The
S signal is connected to the second channel and
panned full left. Take an output from the second
channel and connect to the third channel panned full
right and phase reversed (via a phase reverse switch
or via the cable). (To set the correct S signal level - set
the pan controls of channel two to central, set the main
fader to normal level and set the correct level at the
preset. Then, set the pan control of channel 3 to
centre, set the main fader to the same level as channel
two and then adjust the pre-set of channel three until
the signal totally disappears the two channels are
now set identical now pan channel two fully left and
channel three fully right for normal operation).
Channels two and three are controlled as a single
fader (mechanically or electrically coupled together).
The stereo width is controlled by the relative levels
less side is a narrower image, more side is a wider
image. The displacement of the faders by 3 dB, as
shown in the diagram as an example, results in 1:1
ratio matrixing.

During matrixing, it should be taken into account that
the direction of off-axis sound signals can be
determined less and less at high frequencies due to
the increasing directivity of the shotgun microphone.
This may lead to diffused spatial effects, which can be
desirable or undesirable depending on the recording
situation. In case of doubt, the proportion of the S
signal should not be chosen too high. In some cases, it
might be necessary to reduce the treble in the S
channel on the mixing console. At low frequencies
below 300 Hz, it is very difficult to locate sounds for
physiological reasons. Since the S system of the
microphone, due to its design principle, is more
sensitive than the M system to low-frequency
interference caused for example by wind, the bass in
the S channel should be reduced if required (eg: with a
high-pass filter)."
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