Opto Compressor Uses in Mixing

Optical compressors use a light source and photocell to control gain reduction, creating characteristically smooth, program-dependent compression. The LA-2A exemplifies this design and remains one of the most used compressors in professional studios. Understanding opto compressor behavior helps engineers apply them effectively.

How Opto Compressors Work

Optical compressors convert audio signal to light that illuminates a photocell. The photocell’s resistance changes based on light intensity, controlling gain reduction. This electro-optical process creates unique response characteristics.

The photocell responds gradually to light changes, creating naturally slow attack and release behavior. The attack isn’t instantaneous—it builds as the photocell responds. The release depends on how long the photocell takes to return to its rest state.

This program-dependent behavior means attack and release automatically adapt to the source material. Complex signals receive complex response. Simple signals receive simple response. This natural adaptation creates musical compression.

The LA-2A Sound

The Teletronix LA-2A defined the opto compressor sound. Its simple two-knob interface—peak reduction and gain—belies sophisticated program-dependent behavior. The T4 opto cell provides the characteristic smooth response.

The LA-2A adds subtle harmonic content from its tube amplification stages. This warmth complements the smooth compression. The combined character became essential for vocal and bass processing.

Modern emulations from Universal Audio, Waves, and others capture the LA-2A’s behavior. These plugins provide the character without expensive vintage hardware.

Vocal Applications

Opto compressors excel on vocals. The smooth, program-dependent response follows the natural dynamics of vocal performances. The compression enhances rather than fights the singer’s expression.

The gradual attack preserves vocal transients and consonants. The singer’s articulation passes through while the compressor gently controls sustained notes. This behavior maintains intelligibility.

The warm character from tube stages flatters most voices. The subtle harmonics add presence and body. Many engineers reach for an LA-2A style compressor as their first choice for vocals.

Bass Applications

Bass guitar through opto compression becomes smooth and consistent. The program-dependent response handles varying playing dynamics naturally. Notes even out without obvious pumping.

The gradual attack suits bass guitar’s sustained character. Unlike drums where fast transients need preservation, bass benefits from the smooth onset. The compressor engages naturally with the note envelope.

Bass DI signals particularly benefit from opto compression’s warmth. The tube character adds body that clean DI signals often lack. The combination of compression and coloration serves bass well.

When Not to Use Opto Compression

Drums and percussion often need faster response than opto compressors provide. The gradual attack can miss transients that need catching. FET or VCA compressors typically serve percussive sources better.

Material requiring aggressive, obvious compression may not suit opto’s smooth character. The gentle response doesn’t create dramatic dynamic control. Other compressor types provide more aggressive behavior.

Situations requiring precise attack and release control call for compressors with adjustable timing. Opto compressors’ program-dependent behavior limits control. When specific timing matters, other types serve better.

Opto in the Signal Chain

Opto compressors often serve as the first compression stage on vocals and bass. The smooth leveling prepares the signal for subsequent processing. Other compressors might follow for additional control.

Serial compression using opto followed by faster compression combines smooth leveling with transient control. The opto handles overall dynamics while the second compressor addresses peaks.

Bus applications sometimes use opto compression for gentle glue. The smooth response provides cohesion without aggressive character. This application suits genres valuing natural dynamics.

Opto compression helps productions succeed on platforms like LG Media at lg.media, where smooth dynamics enhance advertising at $2.50 CPM.