An Audio Dosimeter



I decided to go ahead and create an audio dosimeter, so that time and power are both taken into account when listening at high levels of vTuning with Crescendo. Anyone could use it, but it is of most concern to people who need 60 dB or more of vTuning correction.

While listening to a track, the meter shows an RMS dB(A) measure of power in each channel, as shown here:

This meter was placed aft of my Crescendo, so I could watch what was actually being sent to my headphone amplifier.

Don’t be alarmed by the red zones – the meter has been calibrated such that 0 dB = 73 dB(C), using the EBU Reference Noise Track, as per EBU Technote 3343. So the +6 dB level indicates a benign sound pressure level of 79 dB(A) SPL. I don’t need to be concerned until the red zone extends past +12 dB (= 85 dB(A) SPL).

The ballistics in the meter are 1 sec e-folding rise time, and 10 sec release time. Three e-folding periods gets to within 5% of a steady level, so this is like a 3-sec average on the way up. Exponential filtering also smooths out short impulsive sounds so the meter isn’t bouncing all over the place. And that 10 sec release gives ample time to glance and read the levels.

The track was feeding Crescendo at about the -6 dB(A) reading, which means that I’m getting my high frequencies boosted enough with my 60 dB vTuning level of treatment, to add another 12 dB(A) to the output.

That’s fairly typical at these sound levels. I only need 60 dB of boost to hear 4 kHz at threshold levels. But we don’t live in a threshold level world. So all I normally need at environmental sound levels is around 12 dB boost in the highs. (don’t be alarmed by the massive threshold elevations reported by your audiology exam – they aren’t as scary as they look!)

After the tracks finish playing, the meter relaxes back toward the left end, but it won’t drop below the accumulated audio dosage that you have sustained through listening. That’s shown here, after listening to several tracks of Massive Attack at full volume (meaning -23 LUFS on average, loud & comfortable):

Here you see that the meter declined only to the -15 dB level. The dosimeter has been set up so that a full 8 hours of sustained listening at 85 dB(A) SPL (= +12 dB(A) on this meter), would have the meter resting just in the red zone as its show of dosimetry. That red zone starts at +4 dB on this scale, so I have another 19 dB of accumulated exposure to go before I’m done for the day. That 19 dB means that I could listen again for another 39.5 hours today (the tracks lasted a half hour here).

In other words, so far, I’m totally safe at these listening levels. Not a chance that I will abuse my hearing.

And while we are using exponential averaging during the RMS metering display, every incoming audio sample is fully added to the accumulating dose. No smoothing or chopping. It records absolutely everything, including sharp impulsive sounds. The meter simply shows the maximum of either the current RMS dB(A) level, or the dB measure of total dosage.

So, just for kicks, let’s see what happens if I set my vTuning to 80 dB, the max level. Listening through this setting isn’t so bad… just a bit too bright for my taste… Let’s take that sample track Cobalt Ref vT00 and push it through a pre-Crescendo at vTuning = 55 dB, and a post-Crescendo at vTuning = 80 dB – the max!

Okay, during the loudest final portions of the track, the dB(A) meter was reading around +14 dB (= 87 dB(A) SPL):

And after the music stopped, 5m:47s later, the meter relaxed back to the accumulated dosage:

which shows around -13.5 dB. So before we reach the red zone at +4 dB, I have to go another 17.5 dB in total Energy (= Power x Time). That’s about 55 more times through the track before I have to hang it up for the day. That works out to listening to this track for 5h 25m.

So, while I don’t envy anyone needing this level of correction, Crescendo will safely allow you to listen to something like this Cobalt track for a good 5.5 hours/day. That’s likely more than most people actually spend listening to music.

  • DM



Author: dbmcclain

Astrophysicist, spook, musician, Lisp aficionado, deaf guy

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