RMS is the abbreviation for "Root Mean Square" and is a kind of average sound level. The RMS level (colored lighter blue in Audacity) is generally a better estimate of "loudness" than peak level (there is no absolute measure for "loudness" as what is loud for one person may not be loud for another - loudness is subjective).
- Target RMS level (dB): This sets what the RMS level will be after processing (default -18 dB).
- Normalize stereo channels: Choice: Independently or Linked stereo (default Independently).
When processing a stereo track, if "Independently" is selected, then both left and right channels will be normalized to the same RMS level. This may alter the stereo balance, but will tend to make left and right channel the same overall loudness.
If "Linked stereo" is selected, then both channels are amplified by the same amount. The overall stereo level will be as specified by the Target level, but the channels may have different RMS levels if the RMS levels were different before normalizing. This option preserves the original left/right stereo balance.
Preview is not available in this effect because the plug-in cannot predict what the overall level will be before it has analyzed the entire selection.
Requires Audacity 2.1.3 or later.