[ProAudio] Calibrated playback level

Bob Katz bobkatz at digido.com
Tue Feb 1 07:04:11 PST 2022

I just started using automatic filtering so I realized I had not 
responded to David's question. Sorry for the belated reply:

I used the same method to calibrate playback of the Shuttle launch. A 94 
dB SPL tone that came directly from a mike calibrator accurately 
reflects the gain structure on location. I can't think of of a more 
definitive way to calibrate your playback level than you have chosen. 
Keeping in mind that the perceived loudness will differ for the same 
calibration method, depending on loudspeaker distance, and frequency 
response. So you can document the SPL, but you cannot document the 
perceived loudness.

There is another way:

If you have a calibrated gain mike preamplifier and you know the 
sensitivity of the microphone and the gain structure of the ADC you 
could infer the SPL based on the dBFS levels. I calibrated Metric Halo's 
Spectrafoo in dB SPL for my display of the rocket's SPL over time. Other 
FFT-style programs allow you to set up a calibration. So basically once 
you have set up a method and as long as you are consistent you can 
present graphs, spectrograms, etc. all calibrated in SPL.


Best wishes,


On 9/28/21 3:35 PM, David Josephson via ProAudio wrote:
> Greetings ProAudio,
> As many of you know I have been teaching a few people in the aircraft business about sound and noise and perception, trying to bring in best current practice from psychoacoustics, theater sound and acoustic metrology. They are beginning to get it, and there’s work going on across a bunch of groups focusing on accurate playback of ambient recordings and layering new aircraft sounds into those ambients as if the plane had been flying through them.
> Progress report on the planes … some of them are very quiet. There’s a video of the Joby S4 and some conventional aircraft athttps://www.youtube.com/watch?v=itP8-3j2UZI  … this is an accurate binaural recording made with a setup I provided. You can see lots about the aircraft on the web, it carries a pilot and four passengers. Takeoff/departure maximum is about 65 dB(A) at 300 feet, with almost no tonal or impulsive content, compared to about 30 dB higher for a helicopter of similar capacity. Overflight at 1500 feet is about 20 dB lower; there are six very efficient slow-turning propellers. At the moment the cooling fans inside the motors are louder than the props themselves, but these are being fixed in a coming revision.
> We (and NASA, and some others) are making libraries of ambient soundscape recordings to demonstrate what these things sound like in different neighborhoods. Each ambient includes a 94 dB SPL 1 kHz tone, which gets replaced with 500-2000 Hz filtered pink noise of the same rms level. That’s scaled to play back in the listening space at 94 dB, all speakers operating.
> Is there a simpler way to do this? Any other best-practices for metadata and archiving of ambient sound recordings for consistently accurate playback level would help.
> Thanks
> David Josephson
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If you want good sound on your album, come to Bob Katz 407-831-0233 
DIGITAL DOMAIN MASTERING STUDIO Author: *Mastering Audio* Digital Domain 
Website <https://www.digido.com/> No trees were killed in the sending of 
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