Audio foundations

What is a limiter?

A limiter is a ceiling for your audio: a hard line that no peak is allowed to cross, no matter how loud you get. Here is what it does, how it differs from a compressor, and the honest engineering tradeoff hiding inside every limiter design.

Beginnerstart here

The short answer

A limiter is an audio tool that enforces a maximum level. You pick a ceiling, say -1 dB, and the limiter guarantees that nothing in your signal ever goes past it. Below the ceiling, your audio passes through untouched. At the ceiling, the limiter clamps down instantly and holds the level right at the line. It is the last line of defense between your voice and digital clipping, the harsh crackle you get when a signal tries to be louder than digital audio can represent.

Conceptually, a limiter is a compressor taken to its logical extreme. A compressor turns loud moments down by a ratio: at 3:1, every 3 dB you go over the threshold comes out as 1 dB over. Raise that ratio and the output gets flatter and flatter above the line. Push the ratio toward infinity and the line stops being a slope and becomes a wall: no matter how far over you go, the output stays at the ceiling. That wall is a limiter, which is why you will hear it called a brickwall limiter.

In patchd the limiter is a free node you add to any channel from the + Add Node menu, and it has exactly three controls:

Ceiling (default -1.0 dB). The line nothing may cross. Adjustable from -12 dB up to 0.
Attack (default 0.5 ms). How fast the limiter clamps when a peak hits the ceiling. Half a millisecond is fast enough that a shout gets caught mid-syllable.
Release (default 50 ms). How quickly the limiter lets go after the peak passes, so the moment after a loud word does not stay squashed.

Limitera ceiling nothing gets past

The ceiling in action. A voice waveform approaches the -1 dB ceiling; every peak that would cross the line comes out flattened exactly at it, while everything below passes untouched. The ghosted curve shows what a 3:1 compressor would have done instead: a gentle slope, not a wall. The clamp happens with zero lookahead, so the limiter adds no delay.

Intermediategoing deeper

Limiter vs compressor: safety vs shaping

Since a limiter is mathematically an extreme compressor, why run both? Because they do different jobs, and the jobs want different settings.

A compressor shapes your dynamics. It works on most of your speech, gently and musically: a moderate ratio, a soft knee, and an attack slow enough to let the natural punch of a word through. It is the tool that makes a voice sound even and produced, and the companion to EQ in any voice chain.

A limiter is safety. It should do nothing at all for 99 percent of your audio. Its whole purpose is the one moment the compressor was not set up for: the sudden laugh, the shout at a jump scare, the mic bump. A compressor set for natural speech will let a genuinely explosive peak through several dB hotter than everything else, and if that peak reaches 0 dB it clips. The limiter sits after the compressor and catches exactly those escapes. Compressor shapes, limiter guarantees.

That division of labor is why the limiter goes last among your dynamics processing, after the rest of the chain has done its work. Anything placed after the limiter could push the level back over the ceiling and undo the guarantee.

Setting the ceiling honestly

The obvious ceiling is 0 dB, the absolute digital maximum. The default in patchd is -1.0 dB, and the gap is deliberate. A limiter measures the digital samples, but when those samples are converted back to an analog waveform, the smooth curve between two samples can swing slightly higher than either sample. These inter-sample peaks, called true peaks, can nudge past the sample values by a fraction of a dB. A ceiling of -1 dB leaves headroom for them, so a signal that measures legal stays legal all the way through playback. Streaming and voice platforms also run their own processing on your audio, and handing them a signal parked at exactly 0 gives their processing nowhere to work.

Advancedthe math

The math, and an honest tradeoff

Start with the compressor gain formula and push the ratio to the wall. A compressor above its threshold applies gain of (1/R - 1) times the overshoot. As R grows, 1/R falls toward zero:

gain_dB = (1/R - 1) * (in_dB - ceiling) -> ceiling - in_dB as R -> inf

limiting as the compressor limit

At R = 3, a peak 12 dB over comes out 4 dB over. As R approaches infinity, the same peak comes out 0 dB over: output pinned to the ceiling. An infinite ratio is just a compressor that stopped negotiating.

Now the tradeoff every limiter designer has to face. A limiter reacts to a peak, but even a 0.5 ms attack means the very first fraction of a transient can slip past before the clamp fully lands. Studio mastering limiters solve this with lookahead: they delay the audio by 1 to 5 ms so the detector sees each peak before the listener does, and the gain is already down by the time the peak arrives. Transient catching becomes perfect. But the delay is not free, and it is not negotiable:

added_latency_ms = lookahead_ms

the cost of lookahead

A limiter with 3 ms of lookahead adds exactly 3 ms of delay to everything passing through it, peaks or not. A lookahead limiter reads your audio's mail before delivering it.

In a mastering session nobody cares about 3 ms. In a live monitoring path, where you are hearing your own voice in real time, every millisecond of processing delay stacks on top of your buffer latency, and delays add up fast across a chain of nodes. So patchd's limiter makes the opposite choice, deliberately: zero lookahead, zero added latency. It accepts slightly less perfect catching of the first instants of a transient in exchange for being completely safe to leave in a path you are monitoring live. The 0.5 ms attack keeps the exposure window tiny:

samples = attack_ms * fs / 1000 = 0.5 * 48000 / 1000 = 24

attack window in samples

At 48 kHz, the clamp fully lands within 24 samples of a peak crossing the ceiling. Half a millisecond of grace, then the wall. The wall does not do appointments.

Neither design is wrong. Lookahead is the right call when the audio is not live; zero latency is the right call when it is. What matters is knowing which limiter you are holding, because a mastering-style limiter quietly inserted into a monitoring chain adds delay you will feel and never see labeled.

A ceiling on every channel

In patchd the limiter is a free node, like the gate and compressor. Add it from the + Add Node menu as the last dynamics stage on a channel, leave the ceiling at -1 dB, and it will sit silently until the one moment you need it, then hold the line with no added delay. The engine itself runs about 10.7 ms through the bus at a 512 buffer, and smaller ASIO buffers take it lower; a zero-latency limiter keeps that number honest. patchd is in development now. Join the waitlist and we will tell you the moment it is ready to install.