Air-G Pulse
User Manual
Version 1.0
Dynamic compressor based on Pressure6 by Airwindows.
Original source code published under open license by Chris Johnson.
User Manual
Version 1.0
Dynamic compressor based on Pressure6 by Airwindows.
Original source code published under open license by Chris Johnson.
Air-G Pulse is a dynamic compressor based on the Pressure6 algorithm by Airwindows. Unlike conventional compressors, it has no attack or release parameters: the response speed is part of the algorithm’s character, and changes with the signal level. The result is a compression that pounces — that leaps onto transients dynamically, in a way that is hard to configure incorrectly.
Pressure6 was designed by Chris Johnson as an evolution of the bus compression concept: something that does not ruin the sound of the mix, but adds cohesion, impact and drama. It has its own tonal character — a degree of grit and saturation that is part of its identity — and it works across the entire frequency range in a consistent way.
Its main applications: master bus, drum bus, vocals, guitars, any source where more impact and glue is needed without sacrificing transients.
“This will work like a bus compressor — it might not be obvious whether it’s doing anything. Its job is to not screw up the sound of your mix. The way that it moves might be the best thing for doing full mixes or certain kinds of instruments. It pounces with dynamic attacks.”
Air-G Pulse interface.
The main compression control. It adjusts the compressor’s threshold: the higher it goes, the more aggressively the algorithm acts on the signal. At 0% the compressor does nothing; as it rises, the sound begins to compress and acquire character.
At high COMPRESS values with strong signals, the compressor can reduce the level down to near-silence. This behavior — which Chris Johnson calls dynamic inversion style compression — is what makes transients “pounce” in the mix. It is more dramatic than most bus compressors, but controllable by combining it with PRESSURE.
COMPRESS also controls how quickly the compressor reacts: at higher values, the algorithm responds faster to loud peaks and recovers as soon as the signal drops.
Start with COMPRESS between 30% and 60%. Raise it gradually until transients start to jump out. The 40–70% range is the sweet spot for bus use in most cases.
Controls the output level of the plugin. At 50% the output is at unity gain (0 dB). Above 50% the plugin amplifies; below it attenuates. Its range is −∞ dB to +6 dB.
When compressing hard, the overall level may drop because the loudest peaks are being reduced. OUTPUT allows you to recover that level without affecting the character of the compression.
When active, the plugin applies automatic gain compensation that keeps the output level approximately constant, regardless of the COMPRESS and PRESSURE settings.
Off (default): classic behavior. Raising COMPRESS or PRESSURE may change the output level; OUTPUT must be adjusted manually to compensate.
On: the plugin measures in real time the difference between input and output level, and applies a makeup gain with ~500ms smoothing. The level stays stable.
AUTO GAIN is smart about PRESSURE. When PRESSURE = 0.0 (no audible effect), it does not apply any makeup even if COMPRESS is at maximum. Compensation only acts when there is a real level reduction at the output.
Off: when precise control over the output level is needed, or to accurately evaluate GR through the VU meters.
On: to quickly compare different COMPRESS and PRESSURE settings without the volume changing. Ideal during evaluation and configuration stages.
PRESSURE is the effect intensity control. At 0.0 the plugin is completely transparent; as it rises, more character, compression and harmonic saturation come into play.
PRESSURE and COMPRESS work together: COMPRESS sets the threshold and the compressor’s response speed; PRESSURE decides how much of that processing reaches the output. It is not possible to express the gain reduction as a fixed ratio — the algorithm responds dynamically to the signal level.
Start with PRESSURE at 0.0 and raise it gradually while listening. The point where transients begin to pounce with more impact is generally the ideal working range. Combine with high COMPRESS for more aggression, or with low COMPRESS for a touch of saturation without obvious dynamics.
A high-pass filter applied exclusively to the compressor’s detection signal (the sidechain). It does not affect the audio heard at the output.
Its purpose: when there is a strong kick drum or bass in the mix, they can cause the compressor to react to every hit and produce an unwanted pumping effect. Raising SC HPF prevents the compressor from reacting to those low frequencies.
On vocals, guitars and sources without heavy low-frequency content: keep it at minimum. On drum bus or master bus with a prominent kick and bass: raise to 60–80% to stabilize the compressor’s action.
The two meters show the gain reduction (GR) the compressor is applying in real time, separately for the left and right channels. The needle at 0 means no compression; as the compressor acts, the needle moves to the right.
Although Pressure6 is a linked compressor (the same compression calculation applies to both channels), the meters show the actual level reduction per channel via RMS comparison. On sources where L and R have different levels, the meters may differ slightly, which is an accurate reflection of the algorithm’s behavior.
When the plugin is active and receiving audio, the LED does not simply turn on: it pulses in sync with the project tempo at a half-note rate (one pulse every two beats).
The LED has two behaviors: when the output approaches the limit (above -0.8 dB), it starts to glow gradually. This glow is not persistent — it follows the signal in real time. If the output exceeds 0 dBFS, the LED latches at full brightness and stays on until the user clicks it.
This allows the proximity to the limit to be seen in real time, and intermittent clipping to be detected that would otherwise go unnoticed.
If the LED latches regularly during use, consider:
COMPRESS 40–60%, PRESSURE 5–8, OUTPUT adjusted to unity, SC HPF 60–100 Hz if kick and bass are prominent. The typical result: a more cohesive mix where instruments “pounce” with greater impact without losing dynamic range. Less obvious than other bus compressors, but very effective.
COMPRESS 50–80%, PRESSURE 6–10. The way Pressure6 responds to transients works very well on drums: the kick and snare jump out with greater presence, hi-hats and room compact naturally. SC HPF at 60–100 Hz to prevent the kick sub from dominating the detector.
COMPRESS at maximum, PRESSURE 3–6. Pressure6 at low PRESSURE with high COMPRESS produces a very musical parallel compression effect: the dry signal passes almost intact but with the density and character of the compressor underneath. Ideal on drums, electric bass and master bus.
COMPRESS 30–50%, PRESSURE 7–10, SC HPF at minimum. The compressor follows the vocal’s level variations well without pumping. On acoustic guitar it follows pick attacks particularly well. Raise PRESSURE for more character and peak saturation.
Part of Pressure6’s character is the sine waveshaping saturation that acts on the peaks of the compressed audio. This saturation is most intense at high PRESSURE and diminishes as PRESSURE is lowered. It is not obvious distortion: it is a rounding and peak control that contributes to the plugin’s characteristic grit. To appreciate it, try: COMPRESS 70–100%, PRESSURE 10.0, and listen to how the most extreme transients are softened and rounded compared to PRESSURE=0.0.
Air-G Pulse was developed by Air-G Audio as part of a line of plugins based on the work of Airwindows.
The Pressure6 algorithm is the work of Chris Johnson (Airwindows), whose original source code is published under an open license at github.com/airwindows. Air-G Pulse is a reimplementation of the original algorithm with its own additions: sidechain filter, OUTPUT control, AUTO GAIN, GR VU meters, and clip detection.
To Chris Johnson for his tireless work on Airwindows and for sharing decades of audio processing research completely openly.
Air-G Pulse v1.0 — Air-G Audio. The Pressure6 algorithm is the work of Chris Johnson / Airwindows and is used under the terms of his open license.