A “lookahead” dynamic range limiter to stop peaks above the set threshold value.
Unlike the Soft Clipping Limiter, Broadcast Limiter and LADSPA limiter, this limiter does not use wave shaping distortion to limit the peaks. It is a very fast compressor and is able to limit the maximum peaks without introducing high levels of harmonic distortion.
The limiter is very simple to use and requires little explanation, but for anyone that is unfamiliar with limiters, here’s a few tips.
Limit to (dB): This control sets the maximum peak level. As peaks in the original audio approach this level the gain is reduced so as to prevent the peaks exceeding the set level.
Hold (ms): Holds the gain at the reduced level after a peak is detected so as to prevent the gain from “riding the waveform” which would cause harmonic distortion.
Shorter Hold times allow the peaks to be tracked more accurately and the limiter will respond faster to the dynamics.
If there are high levels of very low bass it will be necessary to increase the Hold time to avoid distortion. The default 10 ms hold time is sufficient for frequencies down to 100 Hz without distortion. To cleanly limit high amplitude, very low frequency bass (down to 50 Hz) the Hold should be increased to 20 ms. Setting the hold to 50 ms is sufficient right down to 20 Hz but the delay before the gain level “recovers” is likely to be too slow for most material.
Make-up Gain (0=No, 1=Yes): When enabled (default) the output is amplified by an amount equal to the “Limit” level. If the input audio has a peak level of 0 dB, the peak output level will also be 0 dB. When disabled the peaks are limited only.
Stereo Tracks: As is normal for this type of effect, the left/right channels of a stereo track are processed independently.
Lookahead: This limiter looks ahead for peaks and will begin to change the gain just before the peak occurs. This ensures that all peaks, no matter how fast they occur, will be caught. The lookahead time is roughly a quarter of the hold time.
Knee: This limiter uses a relatively “soft knee” so as to avoid unnecessary distortion. That is, the amount of compression (compression ratio) progressively increases as the input gets louder. At the “Limit to” level the compression ratio is infinite (brick wall) which ensures that peaks will not exceed the limit.
Creative use: This limiter can be used on its own, or can be used to limit peaks after running a compressor that does not use lookahead (such as the SC4 LADSPA compressor). This can produce “crisper” compression than using a lookahead compressor such as the standard Audacity compressor or Chris’s dynamics compressor.
Over 0 dB input: The input waveform should not exceed 0 dB. Over 0 dB input signals are illegal and will be hard clipped to 0 dB before processing with the limiter. If necessary, the Amplify or Normalize effects should be run before applying this limiter to ensure that the input does not exceed 0 dB.
Current download on Wiki Download Nyquist Plug-ins page:
There is also a “type 3” version that has a drop-down menu to select Make-up gain (for Audacity 1.3.x or later)
Limiter (2) on Wiki Download Nyquist Plug-ins page: