Crown PZM-10 Application Manual page 20

Before explaining how the SASS makes such good stereo
recordings, let's describe how stereo itself works.
How Stereo Works
Normally you listen to stereo over two speakers, one
placed in front of you to the left, and one to the right.
When you listen to a stereo recording of an orchestra,
you can hear strings on the left, basses on the right, and
woodwinds in the middle. That is, you hear an image of
each instrument in certain locations between speakers
(Fig. 51).
Fig. 51 – Stereo images.
If you send the same audio signal to the two speakers,
you hear an image in the middle between the two speak-
ers.
How do recording engineers make
the images appear left or right?
One way is to make the signal louder in one channel
than the other. For example, if you feed the same signal
to both channels, but turn up the volume of the right
channel, the image shifts to the right speaker.
Another way is to delay the signal in one channel. If you
feed the same signal to both channels, but delay the left
channel one millisecond, the image shifts to the right
speaker.
So, various image locations can be created by recording
loudness differences and/or time differences between
channels. We want a sound source on the right to make
a louder signal in the right channel than the left. Or we
want a sound source on the right to make a signal
sooner in the right channel than the left.
This is done with stereo microphone techniques. There
are three basic stereo techniques; coincident pair, spaced
pair, and near-coincident pair.
With coincident-pair miking, a pair of directional mi-
crophones is placed with grilles touching, one mic above
the other, and angled apart (Fig. 52). A sound source to-
ward the right will produce a stronger signal from the
mic aiming toward it than from the mic aiming away
from it. Thus, the right channel will be louder and you'll
hear the image to the right.
With spaced-pair miking, a pair of microphones is
placed several feet apart, aiming straight ahead (Fig 53).
Sounds from a source toward the right will reach the
right mic sooner than the left mic, simply because the
right mic is closer to the sound source. Thus, the left
channel will be delayed and you'll hear the image to the
right.
Fig. 52 – Coincident-pair stero miking.
Fig. 53 – Spaced-pair stereo miking.
With near-coincident miking, a pair of directional mi-
crophones is angled apart and spaced apart a few inches
horizontally (Fig. 54). A sound source on the right will
be louder in the right channel AND delayed in the left
channel. These two effects add together, so you'll hear
the image to the right.
FIg. 54 – Near-coincident stereo miking.
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