SC4 M&S DAD Stereo Compressor - User's guide
SC4
7
MIMIC
The JOEMEEK compressor mimics this effect and instead of the listener's ear
and brain doing the compression, the JM pulls down the sound at precisely the
right moment and amount to fool the ear into thinking that the sound is louder
than it actually is. But doesn't any compressor do that? Actually no.
Although there are many compressors on the market that can be set to the
correct time constants to mimic the effect, the actual gain reduction is never
done properly. The problem is that the human ear is not an engineering device,
it's non-linear in all respects. The psychoacoustic compression effect is like
turning down the volume for an instant; but once there, the relative volumes of
sound are NOT affected further.
Good Engineering Practice says that a compressor should work logarithmically;
for a certain increase of volume, the output volume should rise proportionally
less: That is, for a 2:1 compressor, an increase of volume of 10dB at the input
should produce only 5dB increase at the output, a continuous process where
the more you put in, the more it's pushed down. The JOEMEEK compressor just
doesn't work that way. As volume increases at the input, a point is reached
where the compressor starts to work and the gain through the amplifier is
reduced. If the input level keeps rising, gradually the gain reduction becomes
LESS effective and the amplifier goes back to being a linear amplifier except
with the volume turned down. And this is precisely how the human ear behaves!
So the 'ear' is fooled into thinking that the JM compressed sound is louder than
it really is; but without the strange psychoacoustic effect of 'deadness' that all
other compressors suffer from.
ROCK CONCERTS
The second form of compression in the human ear is mostly mechanical. It
involves certain parts of the inner ear being suppressed so that they do not
respond to the large vibrations caused by loud noise. The effect is much
slower to take effect and can take days to recover. This is the familiar
'deadening'
effect that we all get in extreme cases when going to a rock concert. One of
its effects is to change the way that we perceive different frequency ranges.
Basically, the louder the sound, the more we hear of the HF and LF parts
because our sensitivity to the mid ranges is reduced. The JM compressor,
because of its bendingof the loudness contours has already fooled the ear into
thinking that the sound is louder than it really is; the bonus is that the mid
ranges seem to jump forward and the clarity improves because the mechanical
changes that the brain thinks have taken place in the inner ear, have not
happened. With conventional compressors the 'fooling' effect is not so complete
and the ear perceives something that is not quite right.