A slew limiter, also known as a lag processor or portamento module, is a module in a modular synthesizer that smooths out sudden changes in a control voltage (CV) signal or an audio signal by adding a glide or lag between voltage transitions. This results in a gradual change from one voltage level to another, rather than an abrupt jump.
Slew limiters are often used for the following purposes:
- Portamento effect: By applying a slew limiter to a pitch CV signal, you can create a portamento or glide effect between notes, causing the pitch to smoothly transition from one note to another instead of jumping instantaneously.
- Smooth modulation: Slew limiters can be used to smooth out abrupt changes in CV signals used for modulation, such as LFOs, envelopes, or sequencer outputs. This can help create more organic and less abrupt modulations in parameters like filter cutoff, amplitude, or oscillator frequency.
- Envelope shaping: Applying a slew limiter to an envelope signal can alter the shape of the envelope, such as changing the attack and decay times or transforming a simple gate signal into a rudimentary envelope with adjustable rise and fall times.
- Audio-rate processing: While primarily used for CV processing, slew limiters can also be used to process audio signals, generating interesting harmonic content and timbral changes by rounding off sharp waveform transitions.