Compression Techniques
Summary
Abstract
Compression is the most discussed technical topic in mixing-talk (2,443 categorized messages). The community’s approach centers on understanding the four main compressor topologies — VCA, FET, opto, and variable-mu — and learning when each is appropriate. Nomograph Mastering’s pinned compressor guide (62 reactions) is the channel’s definitive resource, recommending engineers pick one model from each category and master it before branching out. Parallel compression, bus compression, and sidechain techniques are extensively discussed practical applications.
Detail
The Four Compressor Topologies
The community consistently returns to the four main compressor types as the foundation of compression knowledge:
VCA (Voltage Controlled Amplifier): Fast, precise, and clean. The SSL Bus Compressor is the defining example. VCA compressors excel at “glue” — making individual elements feel like a cohesive mix. Used extensively on mix buses, drum buses, and stem groups.
FET (Field Effect Transistor): Aggressive, fast, characterful. The UREI 1176 is the quintessential FET compressor with the fastest attack time (~20 microseconds). Known for adding energy and excitement, particularly in “all buttons in” mode for parallel compression on drums.
Opto (Optical): Smooth, program-dependent, musical. The Teletronix LA-2A is the classic example with its T4B opto cell creating naturally musical compression. The community favors opto compression on vocals, bass, and acoustic instruments where a gentle, transparent touch is needed.
Variable-mu (Tube): Warm, gentle, harmonically rich. The Fairchild 670 and Manley Vari-Mu are the reference points. Used for subtle bus compression where harmonic enrichment is as important as dynamic control.
Source
Author: Nomograph Mastering — Date: 2024-12-23 — Channel: mixing-talk “Ok, so that’s a quick summary of the four main types of comp. My suggestion is to pick one model from each category. One and only one. Forget the rest for a while. Start trying it in various places to develop a feel for what each type does.”
Parallel Compression
Parallel Compression (aka New York compression) is one of the most frequently discussed techniques. The approach involves blending a heavily compressed signal with the unprocessed original to add density and sustain without sacrificing transients. Common applications:
- Drums: An UREI 1176 in all-buttons mode on a parallel send is the community’s go-to for adding power to drum buses
- Vocals: Gentle parallel compression to add body and consistency while preserving natural dynamics
- Mix bus: Subtle parallel compression for overall mix density
The community prefers dedicated parallel sends over plugin wet/dry knobs for more precise control over the blend.
Bus Compression
Bus compression is applied to grouped signals (drum bus, vocal bus, instrument bus, mix bus) to create cohesion. Key community insights:
- Slow attack, fast release on the mix bus lets transients through while adding glue
- 2-4 dB of gain reduction is the sweet spot for most bus compression — more than that and you’re likely over-compressing
- The SSL Bus Compressor at 4:1, slow attack, auto release is the starting point most members reference
- Multiple members use front bus / background bus architecture with different compression approaches on each
Sidechain Compression
Sidechain compression uses one signal to trigger compression on another. The most common application is kick drum triggering bass compression to create space in the low end. The community also discusses:
- Sidechain HPF on compressors to prevent bass frequencies from triggering unwanted gain reduction
- Multiband sidechain (using Soothe2) for frequency-specific ducking
- Vocal sidechain on instrument buses to create automatic space for vocals
Settings by Source
Community-shared starting points:
| Source | Compressor Type | Ratio | Attack | Release | Notes |
|---|---|---|---|---|---|
| Lead vocal | LA-2A / opto | 3:1-4:1 | Medium | Auto | 3-5 dB GR |
| Drum bus | SSL / VCA | 4:1 | Slow (30ms) | Fast | Let transients through |
| Parallel drums | 1176 / FET | 20:1 | Fast | Fast | All-buttons or high ratio |
| Bass | LA-2A / opto | 4:1 | Medium | Auto | Smooth, consistent |
| Mix bus | SSL / VCA | 2:1-4:1 | Slow | Auto | 1-3 dB GR max |
| Acoustic guitar | Distressor | 2:1 | Medium | Medium | Gentle, transparent |
Practical Application
- Learn one compressor per topology before expanding your collection
- Set up a dedicated parallel compression bus rather than using wet/dry knobs
- Use the HPF on your compressor’s sidechain to prevent low-frequency content from dominating the gain reduction
- Start with less compression than you think you need — 2-3 dB of gain reduction on most sources
- Listen for “pumping” and “breathing” as signs of over-compression or wrong attack/release settings
Common Mistakes
- Using the same compressor type on every source without considering what each topology does best
- Over-compressing the mix bus and destroying dynamic range
- Not using the sidechain HPF, causing bass-heavy sources to pump
- Stacking multiple compressors without understanding what each one is contributing
- Chasing gain reduction numbers instead of listening to the musical effect
See Also
- Parallel Compression — dedicated glossary entry
- SSL Bus Compressor — VCA bus compression standard
- UREI 1176 — FET compression reference
- Teletronix LA-2A — optical compression reference
- Empirical Labs Distressor — versatile multi-mode compressor
- Mix Bus Processing — bus chain context
- Gain Staging — levels before and after compression
Source Discussions
Discord Source
Channel: mixing-talk — Date Range: 2021-08 to 2026-02 Key contributors: Nomograph Mastering, cian riordan, chrissorem, BatMeckley, Ross Fortune, Slow Hand, ALXCPH Message volume: 2,443 categorized messages
Discord Source — newbie-questions
Channel: newbie-questions — Date Range: 2021-02 to 2026-02 Beginner compression context: BatMeckley (13 reactions): “Honestly, that line [gain staging on the way in] is a bit over blown. It’s more ‘oh the chorus is louder, let’s knock it back a click or two on the input so it doesn’t distort.’ We were fairly conservative on the 1176 on the way in, largely cause you can’t un-crunch a vocal that’s been over compressed.” Nomograph Mastering (12 reactions): “Most of your perceived loudness comes from the arrangement and mid range focus (2k to 8k).” See also: Mixing Basics
Discord Source
Channel: general-talk — Date Range: 2021-02 to 2026-02 Message volume: 638 mixing-categorized messages (360 from verified experts) See also: general-talk Channel Summary