Owner`s manual

9
Why reduce the dynamic range? Consider the problem of mixing the vocal
in a contemporary rock or pop song. Typically, pop music has a relatively
consistent level of loudness. If an uncompressed vocal track is added to a
typical pop mix, loudly sung words or syllables would jump out of the mix,
while quieter phrases would be buried beneath the instrumental texture.
This is because the difference between the loudest and softest sounds in
the vocal - its dynamic range - is very large. This same problem occurs for
any instrument which has a dynamic range larger than the music bed into
which it is being mixed. (For that reason, most instruments, not just vocals,
undergo some compression in the typical mix.)
By using a compressor to decrease the dynamic range of the vocal, the
softer sounds are increased in loudness and the loudest sounds are re-
duced in loudness, tending to even out the overall level of the track. The
overall level of the compressed track can then be increased (using what is
referred to as “make-up gain”), making the vocal track louder and more
consistent in level, and therefore easier to hear in the mix.
Threshold and Ratio
How is compression measured? What is a little compression and what is a
lot of compression?
The effect a compressor has on a track is determined by the settings of its
threshold and ratio. The threshold is the level above which the signal is
attenuated. The ratio is the measure of how much the dynamic range is
compressed.
The graph shown below shows the relationship between the input level of
a signal and the output level of the signal after compression. Notice that
signals that are louder than the threshold are compressed (reduced in
level) while those softer than the threshold are unchanged.
As the input signal exceeds the threshold, gain reduction (reduction in
loudness) is applied. The amount of gain reduction that is applied depends
on the compression ratio. The higher the compression ratio, the more gain
reduction is applied to the signal.
The graph shows the relationship between compression ratio and gain
reduction. Examine the 2 to 1 ratio curve. For signals above the threshold,
this setting transforms a range of loudness 2 units large into a range of
loudness one unit large (i.e., if the input signal gets “x” units louder, the
compressed signal increases by only “x/2” units).