Voice Processing Tu to ri alChapter 6
Basics
The Symetrix 528E Voice Processor com bines Symetrix program controlled interactive dynamic
range processing technique with a three-band parametric equalizer. This com bi na tion of proces-
sors is similar to a voiceover or vocal signal processing chain as used in a recording or voiceover
studio. Program controlled means the 528Es dynamic range processor section analyzes in com ing
signals, then adjusts its release time to match the transient characteristics of those signals.
This chapter of the manual contains a tutorial on the basics of dynamic range pro cess ing and
equalization: the two key ingredients in the 528E. The tutorial information is intended to provide a
background for the information found in the remainder of this manual.
Dynamic Range Pro cess ing
Dynamic range processors are used to t wide-range signals into narrow-range transmission or stor-
age channels. The dynamic range of acous ti cal signals found in real life usually far exceeds our ca-
pacity to store or transmit them. Con front ed with this dilemma, audio engineers usually reach for a
compressor/limiter or down ward expander as a means to t two-pound signals into one-pound bags.
Compressor/limiters respond quickly to tran sients, and gently to normal speech level changes which
keeps overall levels in check. The downward expander?s operation is the inverse of the com pres sor/
limiter which prevents pump ing and breathing even when high ratio compression is neces-
sary. Because the com pres sor/limiter and the downward expander are interactive, the 528E always
responds ap pro pri ate ly, while pro vid ing automatic control over a wide range of input levels.
Strictly speaking, the terms compressor and limiter refer to two different devices. Oftentimes the
two are combined into a single device called a com pres sor/limiter. Com pres sor/limiters usually
perform as either a com pres sor or a limiter, but not both at once. Functionally, a compressor/limiter
is a device that lets the user de ne, or predetermine, the maximum level of an audio signal.
Expanders and gates are the functional opposites of com pres sors and limiters. Compressors con tin u-
ous ly reduce the dynamic range of signals that are above threshold, while expanders con tin u ous ly
increase the dynamic range of signals that are below threshold. Limiters can be thought of as very
high ratio compressors, and gates can be thought of as very high ratio ex pand ers.
In addition to their roles as remedial signal processors, compressors also have a creative role.
You can use a compressor to increase the apparent sustain of a guitar, increase apparent loudness,
improve the consistency of a bass by removing or reducing level changes, and many other things.
Generally speaking, the settings for these applications are somewhat extreme, so experimentation is
the name of the game.
De ning Dynamic Range
To begin a discussion of dynamic range processors its necessary to have a working de nition of
dynamic range. The term is really self-descriptive, but has two distinctly different uses:
1. To describe the actual range of signal uctuations that are going through the equipment.
2. To de ne the maximum allowable range of signal uctuations that can be put through the
equipment.
The usual unit of measure for audio signals is the decibel (dB).
Dynamic Range as a Speci cation
The maximum usable range of operation for a particular circuit or piece of gear is the distance in dB
between the noise oor and the maximum output level. In this context, dynamic range is used as an
equipment speci cation.
Noise oor is de ned as the lower limit of a circuits operating level, and is a function of its self-
528Egenerated electrical noise. Very noisy circuits have a high noise oor, quiet circuits have a low noise
? oor. All circuits have a noise oor, unless they are operating at -460 degrees Fahrenheit (absolute
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