<<let's say the
narrator(or whatever subject of interest - a close-up frog at the
edge of a pond full of croaking frogs in a field of chirring
crickets?) is 12 inches in front of the M mic, and the S mic is
capturing the forest sounds to provide the ambience to go with it.
The M mic signal will have very little of the forest ambience
relative to the narrator's voice, the majority of the forest
ambience will be in the S mic signal. When summed to mono, the S
signal disappears and takes most of the forest ambience with it,
while the M mic signal doubles in amplitude. This creates a
significant difference between the stereo and mono versions of the
same recording, so in that respect it is reasonable to question the
validity of claims that MS is mono compatible because it depends on
what you mean by 'mono compatible'.>>
This is an interesting example, & may illustrate why there might be a
nomenclature issue at play in this discussion. I think this example
shows that the Mid & Side elements will contain distinctly different
information, leading to a sum not containing the width component,
therefore not fitting the description of mono compatible. In my
opinion, the proximity of the array to the narrator, & the distance
between the narrator & any ambient sources, means this constitutes in
effect a multitrack recording, not a true stereo field. Since the
narrator is not integrated into the ambience & each mic is picking up
distinct information, we have something closer to two mono sources
rather than stereo. It's a very clever implementation of mic
technique to achieve a legitimate effect, but when the subject exists
solely in the Mid channel & is entirely in the null of the Side, I
don't feel we can refer to that as stereo. Then again, properly
decoding such an MS signal will be largely a matter of opinion
anyway, since levels will be quite different & the material will not
be coherent.
Since this subject has somehow become highly charged & vaguely
personal, I will reiterate that this is opinion about what
constitutes "stereo" & not scientific fact concerning sum &
difference math. And I also feel that true stereo, i.e. audio
reproduction which mimics the ear/brain's sense of aural emplacement
in three dimensional space, includes depth information in addition to
width. The example of the narrator miked in MS at a distance of 12"
will not convey depth nor width for the narrator.
Scott Fraser
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