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<p>Hi, David,</p>
<p>It comes as no surprise that you and the other scientists have
included the calibration tone in the recording.</p>
<p>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. <br>
</p>
<p>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).</p>
<p>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.</p>
<p>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*"<br>
</p>
<p>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.<br>
</p>
<p>Cheers,</p>
<p>Richard</p>
<p>* 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.</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 2021-09-28 3:35 p.m., David
Josephson via ProAudio wrote:<br>
</div>
<blockquote type="cite"
cite="mid:EF8633CF-BA09-462F-9D61-C70F05DC9105@josephson.com">
<pre class="moz-quote-pre" wrap="">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 <a class="moz-txt-link-freetext" href="https://www.youtube.com/watch?v=itP8-3j2UZI">https://www.youtube.com/watch?v=itP8-3j2UZI</a> … 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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</pre>
</blockquote>
<pre class="moz-signature" cols="72">--
Richard L. Hess email: <a class="moz-txt-link-abbreviated" href="mailto:richard@richardhess.com">richard@richardhess.com</a>
Aurora, Ontario, Canada <a class="moz-txt-link-freetext" href="http://www.richardhess.com/">http://www.richardhess.com/</a>
<a class="moz-txt-link-freetext" href="http://www.richardhess.com/tape/contact.htm">http://www.richardhess.com/tape/contact.htm</a>
Quality tape transfers -- even from hard-to-play tapes.</pre>
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