As I wrote previously the Frog / pond /narrator example is by no means a
proper MS recording. Interesting yes, proper MS no way.
Simple algebra is for sure a great way of explaining MS
Eg
Add M&S =3D Left (twice as loud)
Subtract S from M =3D Right (twice as loud)
The idea that Left + Left =3D 2Left very much assumes both mics "hear" the=
Left {or Right} in the same way.
Ideally both mics should have the same frequency response (this is unlikely=
to be true unless one uses a matched pair of Fig8's) but much much more
importantly the mics need to be as Coincident as possible for this L+L=3D2L=
to
work!
Ok. that's "proper" MS
But it's quite possible to do some interesting & useful things using MS lik=
e
techniques but one must understand the fact that the "S" channel whether
"proper" or otherwise will be lost - cancelled - gone if heard in mono.
An example of what I call phoney MS.
A camera is looking in profile at a couple of actors, driver & front seat=
passenger in a car. There are small omni mics hidden on the "artists" that=
are mixed to mono - the mix will have clear dialogue a few dB's higher than=
the car noise. A 3rd mic is placed in the car such that it picks up mostly=
car noise (& a V little dialogue). We "pretend" the mix is M & the 3rd mic=
is S.
The result heard in stereo is the dialogue stays central, (there is
insufficient dialogue level in the "S" to shift it) but the relatively smal=
l
amount of car noise in the M will interact with the near pure car noise of=
the S to create a distinctly stereo sounding but ultimately directionless
stereo effect. Now if heard in mono all the extra noise from the S goes &
one is left with the dialogue at a subjectively sensible level above the ca=
r
noise. So the mix works for mono & stereo listeners.
John L
Scott Fraser
| <<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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