Overpressure

Quick start

From clean control to full aggression.

The window

Laid out the way the sound flows: in on the left, out on the right.

Header

The preset bar (previous, next, the list, SAVE), the power button (bypass) and the menu (three lines) with this manual. Click the logo for the version and credits.

IN meter

The level going into the compressor, after the Input knob.

Gain reduction

The needle rests at 0 on the right and swings left as the compressor works, up to 20 dB.

Compressor

Input, Threshold, Attack and Decay to the left of the big Ratio knob; Auto Makeup, Saturation and Output to its right.

FX Aggression

Overdrive, Distortion and Fuzz, each with a switch and an Amount knob, and the Low-pass filter.

OUT meter

The level leaving the plugin, after everything.

Signal flow

Eleven stages, in this order, top left to bottom right.

The order matters. The compressor comes first, so the drive stages receive a signal whose level has already been evened out: the grit stays consistent instead of coming and going with every loud note. The filter comes after the drive, so it can take the edge off the harmonics the drive creates. The output gain is last, so it never changes how hard anything is driven.

The stages in the dashed frame bend the waveform, which creates new, higher frequencies. They run at four times the sample rate to keep those from folding back as aliasing; see Oversampling.

Input & meters

Set the level going in, and watch three meters.

Input

Gain before everything else. Turning it up pushes more of the signal over the threshold and into the drive stages: the "hit it harder" control. −24 … +24 dB

Output

Gain after everything else, for matching the level with the bypassed sound. Auto Makeup adds to it. −24 … +24 dB

Both gains glide to a new value over 20 ms, so turning or automating them never produces zipper noise.

Level meters

The IN and OUT meters show peak level per channel on a scale from −60 to +6 dBFS, with more room given to the loud end. Each bar rises instantly and falls at 24 dB per second; a thin line holds the highest peak for 1.5 seconds. The small lamp above a meter lights when the level has gone over 0 dBFS and stays lit until you click the meter.

Gain reduction meter

The needle shows how many decibels the compressor is turning the signal down right now, from 0 (at rest, on the right) to 20 dB. It follows the largest reduction in each moment, so short dips on drum hits are visible.

Compressor

A feed-forward, stereo-linked peak compressor with a soft knee.

Feed-forward means the compressor measures the signal coming in, not its own output, so what you set is what you get: a 4:1 ratio is 4:1. Stereo-linked means one measurement, the louder of the two channels at each instant, sets one gain that is applied to both channels. A loud sound on the left therefore turns the right down by the same amount, and the stereo image stays where it was.

Threshold

The level above which the compressor starts turning the signal down. Lower it for more compression. It is measured after the Input knob. −60 … 0 dB

Ratio

How firmly levels above the threshold are held back. At 4:1 a signal that goes 4 dB over the threshold comes out only 1 dB over. 1:1 does nothing; 20:1 is, in practice, a limiter. The knob gives the low ratios the most travel. 1:1 … 20:1

Attack

How quickly the gain is pulled down when the level rises. Fast catches the front of each hit; slow lets the transient punch through before the squeeze. 0.1 … 100 ms

Decay

How quickly the gain recovers when the level falls: the release. Fast is loud and can pump; slow is smooth and holds the level down between hits. 10 … 1000 ms

The soft knee

How attack and decay work

At every sample the gain computer says how many decibels of reduction the current level calls for. The compressor does not jump there: it moves the actual reduction towards that target a fixed fraction of the way each sample. When more reduction is called for it uses the Attack time, and when less is called for it uses the Decay time. Each time is how long it takes to cover about two thirds (63 %) of the distance; after three times as long it has all but arrived.

The smoothing happens in decibels, so a release sounds the same whether the compressor was working by 3 dB or by 20 dB: a steady rise, not a rush at the end.

Auto makeup

Gives back the level the compressor takes away.

Compression turns the loud parts down, so the result is quieter. AUTO MAKEUP adds gain at the output to compensate, worked out from the threshold and ratio alone:

makeup = ½ × (−threshold) × (1 − 1 / ratio)

That is half of the reduction a full-scale signal would receive. Half, because real music spends most of its time well below full scale, and giving back the whole amount would make everything too loud.

The makeup follows the two knobs, not the music: it does not ride the level or react to what is playing, so it never pumps. It is added to the Output knob, which stays free for the final trim, and it glides when you move Threshold or Ratio.

Saturation

A soft ceiling that rounds the peaks.

SATURATION sits right after the compressor and is always in the path; at 0 % it does nothing. Turning it up blends in a smoothly curved limiter (a hyperbolic tangent): quiet signals pass exactly as they are, and the louder a peak is, the more it is rounded off and held under a ceiling.

Because Saturation lowers peaks, the signal gets quieter as you turn it up on loud material. Bring the level back with Output, or drive it harder with Input.

FX Aggression

Three kinds of drive, mild to wild, each with a switch and an amount.

The stages run in a fixed order, Overdrive → Distortion → Fuzz, and each one only when its switch is lit. Use one, or stack them: each stage then distorts the output of the one before it. Switching a stage on or off crossfades it over 20 ms, so you can do it while the music plays.

Every AMOUNT knob sets how hard its stage is driven: how much the signal is amplified before it hits the clipping curve. Each stage then turns its own output back down by part of that gain, so more Amount means more grit and only somewhat more volume.

Each stage's output against its input, from −1 to +1, at three Amount settings. The steeper the middle and the flatter the ends, the more the waveform is squared off.

Overdrive

A warm soft clip, like a valve stage pushed past its comfort zone. The curve is smooth (a hyperbolic tangent) and slightly lopsided: the positive and negative halves of the wave are rounded a little differently, which adds even harmonics as well as odd ones and gives the tone its body. Up to 30 dB of drive. 0 … 100 %

Distortion

A harder, symmetrical clip. The curve bends more abruptly (a cubic) and then stops dead: tighter and more aggressive than Overdrive, with a strong odd-harmonic bite. Up to 36 dB of drive. 0 … 100 %

Fuzz

A hard clip with a deliberately off-centre operating point. The signal is pushed sideways before it is cut off flat, and the two halves are cut at different heights, so the result is a ragged, lopsided square wave: splatty, buzzy and thick with harmonics. More Amount also pushes it further off-centre. Up to 48 dB of drive. 0 … 100 %

Filter

A low-pass after the drive, to choose how bright the result is.

Low-pass

Removes what lies above its frequency, with a slope of 12 dB per octave and no resonance peak (a flat, Butterworth response). Fully clockwise, at 20 kHz, it is out of the way. The knob gives the low frequencies the most travel. 200 Hz … 20 kHz

Drive creates harmonics all the way up the spectrum, and fuzz in particular can turn fizzy. Turning the filter down to between 3 and 8 kHz behaves much like a guitar speaker: the body of the distortion stays and the fizz goes. On clean settings, a cutoff around 12–14 kHz takes a little air off for a tape-like softness.

The cutoff glides to a new value over 50 ms, so sweeping or automating it is smooth. It works at the normal sample rate and never goes above 45 % of it.

DC blocker

Just before the filter, a gentle high-pass at 10 Hz removes any constant offset. Overdrive and Fuzz are lopsided on purpose, and lopsided clipping shifts the whole waveform away from the centre line. That shift is inaudible but would waste headroom and upset the next plugin; the blocker takes it out without touching anything you can hear.

Oversampling

Why the drive sounds like drive and not like digital hash.

Bending a waveform creates harmonics above the original sound. In a digital system, harmonics that land above half the sample rate cannot exist; they fold back down to frequencies that have nothing to do with the music. That is aliasing, the harsh, metallic edge of cheap digital distortion.

Overpressure runs Saturation and the three drive stages at four times the sample rate (176.4 kHz in a 44.1 kHz session). The harmonics now have room to exist, and the filters that bring the signal back down to the normal rate remove them cleanly before they can fold.

Latency

The up- and downsampling filters delay the sound by a few samples. Overpressure reports this to your host, which lines the track up with the others automatically.

Bypass

The power button crossfades to the dry sound, delayed by the same few samples, so switching it never clicks and never shifts the timing.

Presets

Nine starting points, and room for your own.

Press SAVE in the header to keep your own. Your presets join the list; the preset menu has Save As, Delete and Open Folder, which shows where they are kept as files you can back up or share. An asterisk after the preset's name means you have changed something since loading it.

Every knob and switch is a host parameter and can be automated.

Recipes

Settings to start from; then use your ears.

Specifications

The numbers.