Understanding what does RMS stands for in Audio: Definition & Details

RMS is “Perceived Loudness”

Our ears are sensitive to loudness and tend to average out the loudness coming to it. Human ear and brain can only characterize the audio whether it’s loud, soft or medium. Human ears cannot detect exactly where the peaks and nulls occur in the waveform but we can say how loud or soft the music is.

This is why RMS is the most often used measurement in perceived loudness. As RMS value gets closer to 0dB (maximum), the perceived loudness would also be getting louder.

In audio mastering, this is commonly used and often abused. Bear in mind that extreme adjustments’ audio mastering tools such as Waves LinEQ and L2 Ultramaximizer can squash the audio. This will in turn reduce the differences between loud and soft parts of the music thus the perceived dynamic range are gone although the perceived loudness is at maximum.

In this post on a true measurement of “quality” loudness in audio mastering; the perfect loudness for mastering is not solely based on RMS measurement but a balance between dynamic range and loudness.

Commonly Asked Questions about RMS

1.) What are the differences between RMS and Peak audio?

It has been clearly discussed previously that RMS is more or less the “average” loudness of the waveform whereas peak audio is the maximum. You can also refer to the associated screenshot of the waveform for illustration.

2.) Is there a “standard” RMS levels for mastering?

No, it is encouraged you will read this post on the true measurement of loudness to emphasize the importance of considering dynamics in finding the optimum loudness levels for your master.

3.) Does RMS can be used to describe average power?Like what I’ve seen in home appliances specifications.

Yes, in home appliances it should be well be understood that RMS power (as used by manufacturers, though not entirely an accurate term for that) is AVERAGE POWER. So from the equation (just a very little math):

Average Power = (Voltage RMS) x (Current RMS)

Average power is computed by multiplying the RMS voltage and the current. Thus, you have the average power handling capability of the device whether a hi-fi speakers or studio monitoring equipment.

Average Power specifications are important because it tells the real power/loudness capability of the equipment such as studio monitors/hi-fi speakers. Consider this comparison:

a.) Rated 500 Watts Peak
b.) Rated 500 Watts RMS

Obviously 500 watts RMS is powerful because power rating is now the average unlike 500 watts peak where it’s only the peak that has been considered (it will have a lower average).

4.) Would I compress in terms of RMS or peak?

If you understood the above concepts correctly, you will learn that you should not be compressing in terms of RMS because most audio compression applications are compressing peaks and not averages of the volume. For example, vocalists are known to have an uneven loudness response (sudden loudness transients or soft). By compressing peaks, you can tame the uneven response accurately.

The suggestions provided in the audio compression tips tutorial are compressing the audio in terms of peaks.

5.) How do I measure the RMS of the audio?

Most audio editors comes with RMS measuring capability. A good example is Adobe Audition waveform statistics feature (the screenshots above are created using the tool).

You can check the manual of your audio editor/DAW whether it comes with this feature.

Content last updated on July 5, 2012

  • Hi Emerson, thanks for these great explanations about RMS ! I’m not in the audio domain but could easily understand what is it and how it’s used thanks to your article.