Peak Limiter

A “peak limiter” is a kind of dynamic range compression effect that “pushes down” on peaks so as to reduce their level. Unlike other compressor effects, limiters have little or no effect on the surrounding audio (except for a few milliseconds either side of the peak). They are particularly useful for reducing “transients” (very short loud sounds) that would otherwise prevent the audio from being  amplified without distortion, and can be used creatively for beefing-up drum sounds.

Audacity (2.0.5) currently ships with a “Hard Limiter” LADSPA effect (link to manual) but despite its name and the description in the manual, this is not a “true” limiter in the conventional sense. Rather, the Hard Limiter effect “chops off” the tops of the peaks, then adds back a lower level copy of the peaks. This is less destructive than simply “clipping” the tops of the peaks, but nevertheless it still introduces distortion that can sound quite bad if it affects more than a few occasional peaks.

The peak limiter of this post is a true “fast compression” effect that limits peaks to the specified level without  introducing unwanted distortion.

Limiter plug-in: Download

4 thoughts on “Peak Limiter”

  1. OK & thanks.
    (maybe set the formula to max gain -0.1 and then no red lines.)
    :o)

    Appreciate your time and effort. I couldn’t, easily, get my head around limiter.ny
    I stopped coding before COBOL became passé.
    Mike.

    1. It would e very easy to set the output level to whatever you want, either with a hard coded value or a slider to set the level, but that wasn’t the point of this effect 😉
      This effect was written in response to a common request for how to make a track louder without clipping, so it made sense to set the make-up gain to 0 dB.
      If you want to change the output level, open the plug-in in a plain text editor and change line 19 from:

      to

      The “0.01” is the amount of headroom that you want to allow (on a linear scale of 0 to 1)

  2. Hello.
    I’ve put 3 jpegs up on my home page.
    I’m not sure how to explain this correctly.
    The screen captures are from 30 seconds of a movie soundtrack,
    using Audacity 2.06 with the required Lame plugin.

    Using Peak Limiter with ‘Make-up gain: Off’ I get the expected result.
    Using Peak Limiter with ‘Make-up gain: On’ I get the clipping.

    I was hoping for a max gain with no clipping.
    Is this the expected result?

    Thanks.
    Mike.

    1. Hi Mike,

      The red clip lines indicate that the waveform is “at or above” 0 dB. It is a warning that there “may” be clipping, not that there “is” clipping.

      When makeup gain is enabled, the limiter amplifies the processed waveform to exactly 0 dB. Because the waveform has been peak limited, it is likely that there are many peaks at exactly the same level, which after make-up gain is 0 dB. That’s why there are several red lines showing.

      If you want the peak level to be less than 0 dB (so that no red lines show), then use the Amplify or Normalize effects to change the level to less than 0 dB.

      (If you zoom in really close on the waveform, you will see that those red lines indicate where the waveform “just touches” 0 dB, but there are no peaks “clipped” off).

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