[ProAudio] Calibrated playback level

Richard L. Hess lists at richardhess.com
Tue Sep 28 13:15:38 PDT 2021

Hi, David,

It comes as no surprise that you and the other scientists have included 
the calibration tone in the recording.

Honestly, considering that big round thing under my right hand, I don't 
think that there is any other way. While many professional reproducing 
systems (both studio and theatre) are calibrated for -X dBFS = Y dB SPL. 
There are still "volume controls" that can throw that off.

One thing that I would assume is that the instructions should call for 
measuring it with the meter at "C" or "Flat" weighting, as "A" weighting 
might cause an inaccuracy. (I didn't look at the curve, but my 
recollection is there is a peak around 3 kHz).

I suspect that the $100-300 SPL meters will be close enough for casual 
listening tests, but for serious testing a better meter and microphone 
would provide more accuracy.

I wonder how different playback spaces might affect the perception of 
the noise, even if well-calibrated. Say for example, longer reverb times 
and many hard reflective surfaces vs. the proverbial "pillow factory*"

The work you report on is exciting and thank you for sharing. Have you 
heard anything about the outcome of the attempts two decades or more ago 
to try and use community-level active noise cancellation around Burbank 
Airport? I recall it being announced, and I recall being very, very 
skeptical of its probability for success.



* I must credit "pillow factory" to Dr. Gerre Hancock, the organist and 
master of choristers at St. Thomas Church in NY City where I recorded 
many things (and also attended as a parishioner). In the latter half of 
the 1970s, I was working at the ABC Television Network former facility 
on W66th Street in NY. One Christmas, the Choir of Men and Boys was 
invited to be on Good Morning America and later Gerre asked me, 
"Richard, why do you make all those studios to be like pillow 
factories?" Of course, the choir was used to singing in St. Thomas 
Church which had a reverb time of around five seconds, and the choral 
music did not sound as good in the studio...and I think the choristers 
may have even had problems hearing each other.

On 2021-09-28 3:35 p.m., 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 at https://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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Richard L. Hess                   email: richard at richardhess.com
Aurora, Ontario, Canada           http://www.richardhess.com/
Quality tape transfers -- even from hard-to-play tapes.

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