Sound Pressure, rms, and decibels.

Audacity ver. 2.02, Windows 7 64 bit.
I was wondering, is there a way to figure out sound pressure, decibels, and root mean squared. I’m curious because i am not wanting to damage my ears by increasing the bass, and editing music to be very loud. I would also like to know about finding out the overall frequencies of the songs I’m editing.

Audacity can tell you how big the signal is, but Audacity does not know how loud you are playing it, so Audacity cannot tell you the Sound Pressure Level. For that you would need a Sound level meter

You can analyze the frequencies using “Analyze > Plot Spectrum”:

Radio Shack has offered Sound Pressure Level meters for years. This is their latest offering.


If you are using headphones, an SPL meter won’t give you a usable reading. It’s possible to measure the headphone voltage and calculate dB SPL from the headphone specs, but that’s not very practical. (Speaker specs are not that useful, because the loudness depends on the distance from the speaker and room size/acoustics.)

If you get an SPL meter and play around with it for awhile, you should develop a feel for safe/dangerous sound levels. But, you can be fooled a bit by headphones because they can often go very loud with low distortion, and “in isolation” you loose the “reference” of the background sounds around you.

If you get a Temporary Threshold Shift (if you “feel a little deaf”) for awhile after you turn-off the music, or if you have ringing in your ears after loud listening, there is a possibility of accumulated hearing damage. You can get accumulated hearing damage at lower levels too, but these are clear warning symptoms.

I don’t think loud deep-bass is as dangerous as loud mids/highs. If you can feel the bass in your body, but it doesn’t sound super-loud in your ears, that’s probably safe. But, you might want to do a little research before you take my word on it. :wink:

Sound pressure is simply the intensity (therefore “pressure”) of the air which is moved by a sound wave. Pressure of anything is simply pressure; the addition of the word “level”, as in SPL (sic), is a grammatical gaffe and is unecessary.
Furthermore, when I was taught, decades ago, in English lesssons at school, we learnt that, except for Proper Nouns, the letters of abbreviated words were to be in lower case and each one followed by a full stop. But it seems obvious that this is no longer taught. The “media”, the people who should know better, are amongst the biggest culprits of the destruction of our language.

Decibel notation is a method of indicating a very wide range of measurement using few digits, since it is logarithmic. A dB figure on its own is not a measurement, it is a multiplier. i.e. it tells us how much greater than or less than a given measurement is compared to another. It’s a relative measurement.

3dB on its own tells us that “something” is 3dB greater than “something else”, and -3dB tells us that it is 3dB less than “something else”.

Only when dB is followed by a suffix is it an absolute measurement. For instance 3dBm is a power which is 3dB greater than 1mW, -20dBm is a power which is 20dB less than 1mW. And, since it tells us how much greater or less than “something”, 0dBm means zero times larger (or smaller) than 1mW, in other words 0dBm is 1mW.

There are many other suffixes, some of which are quite obscure and specialised, but an internet search will produce many.
You can find an uncountable number of explanations of decibel calculation too.

Root mean square is a method of calculating the value of d.c. which produces the same heating effect as a given figure of a.c., and is strictly used for voltage or current. But, since you probably had power in mind, that doesn’t help you does it?

The expression of r.m.s. power is a common incaccuracy. What it means is the continuous average power developed in a load when a voltage whose waveform is a sine is applied accross that load.

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