About

x42-limiter (aka dpl.lv2) is a look-ahead digital peak limiter based on Fons Adriaensen's DPL-1. It is intended to be used as final step to avoid clipping when mixing or mastering, but can also be used on individual tracks as well. It comes in mono and stereo variants, the stereo version applies the same gain reduction to both channels.

Latency is 1.2 ms, rounded up to the nearest multiple of 8, 16 or 32 samples depending on sampling frequency. This amounts to 56 samples at 44.1 kHz, 64 samples at 48 kHz, and twice those values for 88.2 or 96 kHz.

The limiter can operate in digital-peak and true-peak mode. This only affects the detection mechanism (key input is 4x oversampled), the live signal itself is not directly affected.

Intersample Peaks
Inter-sample peaks in a sine-wave.

The red line (top and bottom) indicates the digital peak, corresponding to the sampled data (blue dots). The actual analogue sine-wave (black line) exceeds this level. Peaks like these are called intersample peaks, or true peaks.

Screenshots

screenshot

User Interface

The control knobs respond to mouse click and mouse-drag movements:

The Ctrl key allows for fine-grained control when dragging or using the mouse-wheel on a knob.

Hovering the mouse over label below a control displays a tooltip with information.

Parameters

Display

The level and gain reduction display, shows a range from -10 to +20dB with ticks every 5dB.

The meter at the bottom shows the peak signal level after input gain and relative to the threshold which corresponds to the green to yellow transition. The scrolling waveform above the meter shows the gain reduction history, with the range being displayed for every 50 ms segment of the signal.

Acknowledgments

dpl.lv2 is based on Fons Adriaensen's zita-audiotools.