VHL-3C

About the VHL-3C

Inspired by the Pultec HLF-3C: a passive high/low pass filter unit from the early 1950s, built around a cascade of two constant-K filter networks — the tool engineers reached for to shape the extremes of a signal without touching the middle.

The VHL-3C is a vintage high/low pass filter, and it's free. No trial timer, no account gymnastics — download it and it's yours. What you get is an entirely passive filter design with two controls and one job: cleaning up the top and bottom of a signal the way a classic Pultec-style filter did, with the musical, slightly interactive behaviour that only a constant-K network gives you. Reach for it when a track has too much rumble underneath, too much fizz on top, or both.

The Pultec HLF-3C and constant-K filtering

The hardware behind the VHL-3C was a sought-after passive processor from the early 1950s. Its filters weren't sharp digital brickwalls; they were gentle, resonant slopes built from inductors and capacitors that interact with the circuit's load. We modelled that whole passive network — including the filter-stage interaction and the influence of the load resistance — with our real-time SPICE-style circuit simulation, so the filters don't just cut, they colour. That interaction is exactly why the old boxes sound "musical" rather than clinical, and it's baked into the VHL-3C.

Two knobs, and a load switch that changes the character

The layout is deliberately minimal. The Low Cut-Off (high pass) steps through 50, 80, 100, 150, 250, 500, 750, 1000, 1500 and 2000 Hz — or OFF. The High Cut-Off (low pass) runs from 1.5kHz up to 15kHz across stepped positions, or OFF. Set both to their extreme positions and you get a narrow telephone-line bandpass, a classic lo-fi effect on its own. The third control is the one people miss: a Load Z switch between 500 and 600 Ohm. The filter network is designed for a 500 Ohm terminating resistor, so flipping to 600 Ohm gives you slightly overdamped filters — a subtly softer, tamer slope when you want it.

Where the VHL-3C earns its place: mix-bus cleanup and mastering

Slot it across the mix bus and roll the low cut up to 50 or 80Hz to strip sub-rumble and room mud that eats headroom, then trim a touch of harshness off the top with the high cut — instant clarity before your bus compressor. On individual sources it tames boxy low end on guitars or removes hiss and sibilant fizz from vocals and cymbals. In mastering it's a clean, characterful high-pass and low-pass pair for gently focusing a full mix without a surgical EQ's clinical edge. And because it costs nothing, it belongs on every template. Pair it ahead of a colouring EQ like our VEQ-1P when you want to clean up first, then sweeten.

VHL-3C Features

Cascaded constant-K filter network

A cascade of two passive constant-K filters — high pass and low pass — recreates the resonant, interactive slopes of the early-1950s hardware. The filters interact with the circuit load rather than cutting cleanly, which is what gives them their musical, characterful sound.

Stepped low cut-off (high pass)

The Low Cut-Off steps through 50, 80, 100, 150, 250, 500, 750, 1000, 1500 and 2000 Hz, or OFF — repeatable, musical positions for stripping rumble, sub-mud and low-end boxiness.

Stepped high cut-off (low pass)

The High Cut-Off sweeps from 1.5kHz up to 15kHz across stepped settings, or OFF, for taming harshness, fizz and hiss without a clinical brickwall.

Selectable 500 / 600 Ohm load

A Load Z switch changes the terminating resistance. The network is designed around 500 Ohm; switching to 600 Ohm slightly overdamps the filters for a softer, tamer slope — a genuine hardware behaviour, not a cosmetic option.

Telephone-line bandpass trick

Set both cut-off controls to their extreme positions and the two filters close in on each other to produce a narrow telephone-line bandpass — a ready-made lo-fi effect.

Authentic circuit emulation

Our real-time, SPICE-type component-based circuit simulation faithfully models the passive filter network, including the filter-stage interaction and the influence of the different load resistances.

SSE2-optimised code

DSP operations are pipelined on the SSE2 instruction set for high-performance operation even under complex processing.

Auto-adjusted oversampling

A low-latency, linear-phase Dolph-Chebyshev polyphase design attenuates aliasing and auto-adjusts to your session's sample rate to save CPU while staying transparent.

HighDPI / Retina support

Crisp, high-pixel-density rendering on macOS and Windows for a sharp interface on modern displays.

VHL-3C Examples & Videos

VHL-3C — Additional Notes