6
M/S Master
M/S Stereophony
Our ability to identify the direction and distance of a sound source is the essence of spatial
hearing. The human ear can identify level and time differences from ear to ear very precisely
and use that information to localize sound. At frequencies up to 1500 Hz the ear analyzes basi-
cally time differences to localize sound, while above this frequency it uses level differences.
Our hearing provides excellent conditions to apply room information even to artificially gene-
rated sounds. Regardless of the deficiencies and differences that loudspeakers and head-
phones might present during playback, the human ear needs only the signals to be codified
in, at least, two channels, in order to be able to identify time and level variations, which result
in spatial hearing.
This sort of recording and playback that includes spatial information is known as stereophony
(from Greek stereos = solid or three-dimensional). The resulting stereo image is called pano-
rama. Besides the two-channel stereophony there are several other formats of stereophony.
The common conception of „stereo“ as a two-channel recording is thus incorrect.
Equally incorrect is the concept that the encoding of a stereo signal is always done in a right
and a left channel. This idea is based on the fact that we have a right and a left ear and that
all two-channel recording and playback systems use the same right/left format. It is also not
true that all recordings are made with a microphone for the left channel and a microphone for
the right channel.
The differences between the most important microphone techniques have much more to do
with level and time differences. Due to the advantages and disadvantages that each tech-
nique provides, more often than not they are combined during production to achieve L/R play-
back.
While there are several stereo techniques that can be applied during miking, for signal proces-
sing during production there is only one technique that is actually useful: M/S. „M“ stands for
Middle (or Mid) and „S“ for Side, which means that signals are separated from the middle
to the sides, instead of from left to right. M/S can be actually applied during recording: two
microphones with different polar patterns record direct and spatial information.
– Besides the microphone technique, M/S can also be used as an alternative stereo encoding
for signal processing, which means that signals do not necessarily need to be recorded with
the M/S microphone technique to be able to apply M/S encoding afterwards (at the mastering
stage, for example).
In fact, M/S encoding can be generated from L/R encoding by summing and subtracting
signals:
M = L + R, S = L – R
The sum of the left and right signals in the Mid signal corresponds to the mono signal of the
L/R encoding. The Side signal is also created from the L/R signal by inverting the polarity of
the right channel. The sum of phase-inverted signals results in the cancellation of mono infor-
mation in the signals summed; thus, the Side signal is made up of the differences between L
and R. The detailed formula may be clearer: M = L + R, S = L + (-R). The minus sign stands for
the phase inversion.
It is also possible to create a L/R signal encoding from an M/S encoding by summing and
subtracting the signals, what is usually called M/S decoding:
L = M + S, R = M - S
Mathematically, the sum and subtraction of signals guarantees a lossless conversion from
L/R to M/S and back to L/R, which is a very important aspect for using M/S encoding for signal
processing.
Introduction
Summary of Contents for M/S Master 1020
Page 22: ...Manual M S Master Model 1020...
