Engine Modes

Pressure includes five compression engines, each modeling a different hardware topology. The Mode selector switches the entire compression algorithm — not just a filter or saturation flavor, but the fundamental gain reduction behavior.

MIX — VCA

SSL G-Bus character

The VCA engine models the gain reduction behavior of an SSL G-Series bus compressor. It's clean, punchy, and versatile — the default choice for mix bus and group compression.

Ratio range: 2:1 to 8:1 (PRESSURE driven)

Attack: 0.1–100 ms (clamped). Scales from 30 ms at P=0 to 1 ms at P=1.0.

Release: 10–2000 ms (clamped). From 1200 ms at P=0 to 100 ms at P=1.0.

Knee: Scales inversely with ratio — wide (12 dB) at low PRESSURE, narrow (3 dB) at high. This is the defining SSL trait: gentle at low ratios, firm at high.

Sidechain HPF: Controlled by TONE. tone² × 150 Hz, range 20–300 Hz.

When to use MIX

• Stereo bus / mix bus glue
• Group buses (drums, vocals, strings)
• Gentle cohesion on submixes
• Parallel compression blends

INST — FET

1176 “Dr. Pepper” character

The FET engine models a UREI 1176 Limiting Amplifier — the fastest, most aggressive engine in Pressure. At high PRESSURE values, it enters All Buttons In mode (21:1 ratio) for extreme coloring.

Ratio steps: 4:1 (P<60%), 8:1 (P<80%), 12:1 (P<92%), 20:1 (P<97%), All Buttons In / 21:1 (P≥97%)

Attack: 20–800 μs (microseconds, not milliseconds). The 1176 has the fastest attack of any classic compressor.

Release: 50–1100 ms. Follows a V-shaped curve: shortest at P=0 and P=1.0, longest at P=0.5. Formula: 50 + 400 × P × (1-P) ms.

Input drive: Threshold maps to inverted input gain (like a real 1176 where INPUT drives the signal into the detector). Higher PRESSURE = more input drive = more compression.

Saturation: Two-stage FET saturation adds harmonic content. Output gain automatically compensates for input drive and saturation gain.

Sidechain HPF: None. The FET engine does not use sidechain filtering.

When to use INST

• Electric and acoustic guitar
• Bass guitar (drive and sustain)
• Synths and keyboards
• Aggressive vocal compression
• All Buttons In mode for extreme parallel effects

VOCALS — Opto

LA-2A optical character

The Opto engine models the Teletronix LA-2A leveling amplifier. Like the hardware, it has no fixed ratio — compression increases naturally with signal level, creating smooth, musical dynamics control.

Ratio: Continuously variable from 2:1 to 12:1. Not stepped — the optical cell's sensitivity creates an emergent ratio that varies with signal level.

Peak Reduction: Maps from PRESSURE via threshold. At P=0.5, peak reduction is ~30 (moderate); at P=1.0, it reaches 60 (heavy).

Attack/Release: Hardwired in the optical cell model — not user-adjustable. The optical element has inherently smooth, program-dependent timing.

Tube warmth: Subtle 2nd harmonic content scaled by sensitivity: 0.038 + sensitivity × 0.013.

TONE behavior: Controls emphasis (not sidechain HPF). Maps directly to the optical cell's emphasis parameter.

When to use VOCALS

• Lead and backing vocals
• Voiceover and dialogue
• Podcast and streaming voice
• Any source needing transparent, smooth leveling

DRUMS — Dynamics

dbx 160 transparent character

The Dynamics engine is transparent and precise — it controls dynamics without adding color. Its defining characteristic is a permanently hard knee (0 dB), just like the dbx 160.

Ratio range: 2:1 to 8:1

Attack: 3–30 ms. Slightly slower than VCA to preserve drum transients.

Release: 100–300 ms. Auto-release tuning set separately for program-dependent recovery.

Knee: Always hard (0 dB) — the dbx 160's defining trait. No soft-knee option.

Sidechain HPF: Controlled by TONE. tone² × 120 Hz, range 20–120 Hz. Protects kick drum from triggering excessive compression.

When to use DRUMS

• Individual drum tracks (snare, kick, toms)
• Drum bus and room mics
• Percussion and programmed beats
• Any source where transient preservation is critical

MASTER — VariMu

Fairchild 670 tube character

The VariMu engine models the Fairchild 670 variable-mu tube compressor. Its always-wide knee and slow release times make compression nearly invisible — it adds warmth and cohesion without obvious gain reduction artifacts.

Ratio range: 2:1 to 8:1. Variable-mu ratio modulation in the engine makes effective ratio change with signal level.

Attack: Clamped to Fairchild TC range: 0.2–0.4 ms. Always fast, always smooth.

Release: 300–5000 ms. Mastering-grade — the longest release times of any engine. From 5 seconds at P=0 to 300 ms at P=1.0.

Knee: Always wide (10–24 dB, enforced minimum 10 dB). Tube-inherent — the Fairchild specification is 10–15 dB knee width.

Tube warmth: Even harmonics for perceived loudness without actual gain. Formula: 0.23 + tone × 0.32.

Sidechain HPF: Controlled by TONE. tone² × 120 Hz, range 20–250 Hz.

When to use MASTER

• Master bus sweetening
• Stereo mix glue (mastering context)
• Orchestral and cinematic material
• Any source where warmth and transparency matter

Engine Comparison

Feature	VCA	FET	Opto	Dynamics	VariMu
Max Ratio	8:1	21:1	12:1	8:1	8:1
Fastest Attack	1 ms	20 μs	Fixed	3 ms	0.2 ms
Knee	Variable	6 dB fixed	N/A	Hard (0 dB)	Wide (10–24 dB)
SC HPF	Yes	No	No	Yes	Yes
Coloration	Clean	Colorful	Warm	Transparent	Warm

For exact PRESSURE curve values at P=0, P=0.5, and P=1.0, see PRESSURE Control.