PreSonus RC 500 - Manual (Page 11)

RC 500 Owner’s Manual
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3 Tutorial
3.1 A Brief Tutorial on Dynamics Processing
The RC 500 includes a custom FET compressor. What follows is an excerpt
from a brief tutorial on dynamics processing written by PreSonus president
and founder Jim Odom. It is included to help you get the most out of your RC
500. This tutorial will take you through the basics of dynamics processing.
3.1.1 Common Questions Regarding Dynamics Processing
What is dynamic range?
Dynamic range can be defined as the ratio between the loudest possible audio
level and the noise floor. For example, if a processor states that the maximum
input level before distortion is +24 dBu, and the output noise floor is -92
dBu, then the processor has a total dynamic range of 24 + 92 = 116 dB.
The average dynamic range of an orchestral performance can range from
-50 dBu to +10 dBu, on average. This equates to a 60 dB dynamic range.
Although 60 dB may not appear to be a large dynamic range, do the math,
and you’ll discover that +10 dBu is 1,000 times louder than -50 dBu!
Rock music, on the other hand, has a much smaller dynamic range:
typically -10 dBu to +10 dBu, or 20 dB. This makes mixing the various
signals of a rock performance together a much more tedious task.
Why do we need compression?
Consider the previous discussion: You are mixing a rock performance with an
average dynamic range of 20 dB. You wish to add an uncompressed vocal to the
mix. The average dynamic range of an uncompressed vocal is around 40 dB. In
other words, a vocal performance can go from -30 dBu to +10 dBu. The passages
that are +10 dBu and higher will be heard over the mix. However, the passages
that are at -30 dBu and below will never be heard over the roar of the rest of the
mix. A compressor can be used in this situation to reduce (compress) the dynamic
range of the vocal to around 10 dB. The vocal can now be placed at around +5
dBu. At this level, the dynamic range of the vocal is from 0 dBu to +10 dBu. The
lower level phrases will now be well above the lower level of the mix, and louder
phrases will not overpower the mix, allowing the vocal to “sit in the track.” The
same points can be made about any instrument in the mix. Each instrument has
its place, and a good compressor can assist the engineer in the overall blend.
Does every instrument need compression?
This question may lead many folks to say “absolutely not, overcompression is
horrible.” That statement can be qualified by defining overcompression. The term
itself must have been derived from the fact that you can hear the compressor
working. A well-designed and properly adjusted compressor should not be audible!
Therefore, the overcompressed sound is likely to be an improper adjustment on
a particular instrument—unless, of course, it is done intentionally for effect.
The world’s best mixing consoles offer compression on every channel because most
instruments need some form of compression, often very subtle, to be properly
heard in a mix. Punch, apparent loudness, presence—these are just three of the
many terms used to describe the effects of compression. Compression is a form
of dynamic-range (gain) control. Audio signals have very wide peak-to-average
signal-level ratios (sometimes referred to as dynamic range, which is the difference
between the loudest level and the softest level). The peak signal can cause overload
in the audio recording or sound-reinforcement chain, resulting in signal distortion.
A compressor is a type of amplifier in which gain is dependent on the signal level
passing through it. You can set the maximum level a compressor allows to pass
through, thereby causing automatic gain reduction above some predetermined