Measuring Noise Floor

[Chris Bauer]

Okay, I know this is a pre-kindergarten level question but here goes...

If I want to measure the noise floor of a room...

If, say, I want the maximum noise floor to be -60db, does that simply mean that no ambient noise peaks above 60db or, as I suspect, does it mean something else entirely?

If, indeed, it means something else, what’s the best way to measure it?

[Dave Mudgett]

When I think of noise floor, I'm thinking of how many decibels (dB) of RMS (Root Mean Squared) noise signal level lower than the RMS level of whatever is the 0 dB level of whatever signal it is being compared to.

So yes, it's a bit arbitrary, but there are standards for what to consider the 0 dB level of, let's say, music being recorded.

I would not think of ambient noise "peaks", but RMS signal, which is obtained by squaring a signal f(t), integrating it over a sample time interval, dividing by the time interval, and then taking the square root - i.e., for the mathematically inclined:



The RMS calculation is a type of averaging over a time period. But in this case the signal is first squared (to make all signal points non-negative and accentuate large signal values over small ones), and then averaged over the time period.

[Mike Auman]

Chris, to reply to the second part of your question, you can measure the ambient sound pressure level (noise floor) with a smart phone app. I use "deciBel" and "Audizr" on my Android phone (both have free and paid versions) and there are similar ones for iPhones. The results of these are usually good enough, but if you want a higher level of accuracy, you can calibrate the Android apps against a known level or compare them side by side with a calibrated SPL meter. Most iPhone apps are already pretty accurate without calibration. It has to do with the inconsistencies in Android hardware from brand to brand, vs. the sameness of Apple hardware. Best regards, Mike

[Dave Mudgett]

There are a myriad of details on actually computing practical RMS sound pressure levels - wikipedia actually has a pretty good writeup on that: https://en.wikipedia.org/wiki/Sound_level_meter

Dedicated sound pressure meters can be purchased pretty reasonably. But I think most low-end stuff is pretty limited, mostly oriented to safety aspects of sound levels, not low levels like a noise floor. And if you look at the dominant "A" frequency weighting, it heavily de-emphasizes low and low-midrange frequencies. I'd want a meter which gave other options, including unweighted (Z-weighting) as well as both "fast" and "slow" time-weighting.

Just some examples, not pushing amazon - https://www.amazon.com/s?k=Sound+Level+Meter

[Chris Bauer]

Georg - I'm recording for a variety of sites who have varying requirements as far as the noise floor. I'm working in a currently poorly treated room and want to be sure I'm meeting or, hopefully, exceeding the expected standards once the room is appropriately treated.