10/04/2023
VCA – Voltage Controlled Amplifier
The VCA compressors are the most versatile of all types of compressors
Most used type of compression
They are fast, smooth and are not very colorful, thus don’t change the sound characteristics too much
Popular choice for bus compression and mastering
Have all typical controls of dynamic processors: attack, release, threshold, ratio, and knee
Most famous VCAs are the SSL & Neve channel strips compressors, the dbx 160A, and the API 2500
Technical information:
The electrical circuit is split into two paths:
(1) Detector path: When a certain voltage is reached, the compressor turns down the signal, thus controls the compression effect
(2) Output path: Is what you hear in the end
Opto / Optical Compression
Used for vocals, lead instruments, bass and rounding out a performance (think of a long-term event)
Sound characteristics: Smooth, natural and musical sound
Can handle more gain reduction, yet still sounding natural, as the attack and release times are slower overall
Famous Optical Compressors: LA2A & Tube Tech CL1B
Technical information:
Compression depends on light (light-dependent resistors)
The audio signal feeds a light element which operates through a light-sensitive resistor
Resistor acts like a pipe: Gain says how much is going into the pipe and peak reduction says how much is going out of the pipe, or in other words, the more resistance a.k.a peak reduction, the more compression overall
Optical compressors add color as there are many different types of light sources and resistors available
FET Compression
Best use for hard peak limiting tasks (super-fast attack & release times)
If you want something „in your face“ like vocals, you’ll better grab a FET compressor
In general not a good fit on the master bus
They add color to the source material
Most famous: Urei 1176
Technical information:
The electrical circuit is based on transistors (transmitter + resistors) and operates with the electrical field in addition to voltage (not the same as VCA)
Vari-Mu (Variable-Mu by Manley or originally Delta-Mu)
Adds glue and is used not for dynamic control in first place
Gentle type of compression (mix bus)
Sounds like a soft-knee effect
Not suitable for an aggressive type of sound
Adds color without even limiting the material (tubes)
The sound quality is smooth, rich, thick & creamy
Transients are treated in a musical way
Speed response is the slowest compared to the other types of compressors
Can handle more gain reduction before unwanted artifacts occur
Most famous: Fairchild 660 & 670
Technical information:
Compressors are based on tubes
While Opto-Compressors can use tubes for color, Vari-Mu compressors use tubes to tame dynamics
The ratio increases as you push the unit harder, so this technique sounds musical and pleasing to our ears
BONUS
Diode-Bridge Compression
Most colorful compression of all, as a diode itself adds colorful distortion
The Neve 2264 500 series unit is one famous example of diode-bridge compression
PWM - Pulse Width Modulator
A pulse width modulator circuit creates almost no artifacts, thus no color (the cleanest compressors of all)
Extremely difficult to build, thus extremely rare
Modern unit of a PWM compressor: Great River PWM 501
Dnabeatz Erex Muzic
