Acoustic descriptors - 1/3 oct and dBA values

Dear sirs,

This is to ask if Audacity has a plugin able to analyse an audio signal to obtain acoustic descriptors from a calibrated signal.

Would it be possible to record say a 94 dB tone with an acoustic calibrator at the beginning of a long audio recording with a sound level meter, and use Audacity to give calibrated SPL reading and noise descriptors in octave bands?


Rodrigo Olavarria

Audacity does not have a 1/3 octave spectrum analyzer, but it does have “Plot Spectrum

I’m not sure what you mean. “dB” is a ratio, so it must always be with respect to some other level.

For signals, “dB” is generally quoted with respect to “full scale” (dBFS). Full scale in Audacity is the 32-bit float range +/- 1.0, where integer formats are normalized from their full numeric range (some technical info about this here: libsndfile : Frequently Asked Questions.)

Acoustic dB meters are used to measure “sound pressure level” (SPL), which is an RMS measurement where the reference level is “the threshold of hearing” (usually specified as 20 μPa), and may be a “weighted” measurement.

Any signal that is recorded on the computer will be subject to the gain stages of the system. In other words, the level in Audacity depends not only on the input signal level, but on the sensitivity and gain of the sound card input and any gain stages implemented by the sound card drivers.

If you have a known (calibrated) input signal, then by measuring the signal level in Audacity you can calibrate the system, but as indicated above there are a lot of details to take into account so I can’t give a simple answer.