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Limiter vs compressor
Gazillion Industries ·
Two boxes, both turning things down, both with a threshold, both promising
loudness. The difference between them is one number, and knowing which number decides which one
goes at the end of your chain.
A limiter is a compressor with a very high ratio and a very fast attack, set to stop a signal
crossing a ceiling. A compressor shapes dynamics across the whole performance; a limiter catches
the few peaks that would otherwise clip. In practice: use a compressor early, to control and
shape, with 3 to 6 dB of gain reduction on the loud parts. Use a limiter last, with a ceiling
around −1 dBTP, to stop the output going over.
The short version
- Compressor
- ratio 2:1 to 8:1, shapes the whole performance
- Limiter
- ratio 20:1 or higher, often infinite: a ceiling
- Attack
- compressor, milliseconds you choose; limiter, as fast as possible
- Job
- compressor controls dynamics; limiter prevents overs
- Order
- compressor first, limiter last
- Amount
- compressor 3–6 dB; limiter 1–3 dB on peaks only
The line between them
There is no hard border in the circuit, only in the setting. Traditionally anything above
about 10:1 counts as limiting, and a true brickwall limiter behaves as if the ratio were
infinite: nothing crosses the ceiling, ever. Below that you are compressing, which means the
signal still gets louder as the input gets louder, just less so.
The practical distinction is what each is listening for. A compressor is reacting to the body
of a performance, and its timings are musical decisions. A limiter is reacting to a handful of
samples, and its timings are technical ones: it exists so the converter or the encoder does not
receive something it cannot represent.
How to use each
- Put the compressor early, on the track or the bus, and set it by ear for feel.
- Get the balance right with the compressor in, not after the limiter is on.
- Deal with the worst transients before the limiter: a clipper or saturation will shave
peaks without the limiter having to pull down the whole track.
- Put the limiter last, with the ceiling at −1 dBTP for anything that will be
encoded.
- Push into it a decibel at a time and listen to the quiet bars, not the loud ones.
- If the limiter is doing more than 3 dB on average, the problem is upstream.
For the loudness part of that chain in detail, see
clipper before limiter and
how loud should my master be.
DRUGS has both
ends of this on one free panel: a compressor with one knob, and LIMIT, a soft ceiling on the
output at −0.3 dBFS.
Where each one costs you
A compressor costs you dynamics in exchange for consistency, and the cost shows up as a
performance that stops moving. A limiter costs you transients in exchange for level, and the cost
shows up first on drums: the snare goes flat, then the kick, then everything develops a soft
ceiling you can hear. Limiters also pump when pushed, because a fast attack and a slow release
hold the whole mix down after every peak.
Both flatter themselves the same way, through make-up gain. Level-match before deciding.
Questions people ask
Should I use a compressor or a limiter?
Both, in that order, for different reasons. The compressor shapes how the performance moves.
The limiter stops the output exceeding a ceiling. A limiter used as a compressor will flatten
the life out of a track, and a compressor used as a limiter will let peaks through.
At what point does a compressor become a limiter?
Conventionally around a 10:1 ratio, with a fast attack. A brickwall limiter behaves as though
the ratio were infinite, so nothing at all passes the ceiling.
Should the compressor come before the limiter?
Yes. Shape first, catch what is left afterward. A limiter in front of a compressor gives the
compressor a signal whose peaks have already been flattened, so its timings no longer relate to
the performance.
How much limiting is too much?
When the drums lose their front edge and the quiet bars start moving with the loud ones. One
to three decibels of gain reduction on peaks is normal; anything much past that is a mix
problem being solved in the wrong place.
What DRUGS does
DRUGS is our free bus compressor for drums, and it carries both halves of this article.
DOSE is the compression: it moves the transfer curve, the knee, the attack and
the release together, making a drum bus denser rather than louder. GAIN adds 5
dB after the compressor and before the ceiling. LIMIT is a zero-latency soft
ceiling at −0.3 dBFS on the output, with a clip indicator; it attenuates only, and it is
transparent below about −0.9 dBFS. Both are on when it opens.
Two boxes, one number between them. Now you know which one belongs at the end.
Keep reading
DRUGS — a one-knob bus compressor for drums, free for Mac and Windows.
One control called DOSE, with GAIN and a soft ceiling on the way out.
FREE DRUGS