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<p>I just started using automatic filtering so I realized I had not
responded to David's question. Sorry for the belated reply:<br>
</p>
<p>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.<br>
</p>
<p>There is another way:<br>
</p>
<p>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.</p>
<p><a class="moz-txt-link-freetext" href="https://www.digido.com/portfolio-item/we-have-lift-off-now-in-surround/">https://www.digido.com/portfolio-item/we-have-lift-off-now-in-surround/</a></p>
<p><br>
</p>
<p>Best wishes,</p>
<p><br>
</p>
<p><br>
</p>
<p>Bob</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 9/28/21 3:35 PM, 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>
<div class="moz-signature">-- <br>
<pre><font class="3D""" face="3D"Courier"">
If you want good sound on your album, come to
Bob Katz 407-831-0233 DIGITAL DOMAIN MASTERING STUDIO
Author: <b>Mastering Audio</b>
<a href="https://www.digido.com/">Digital Domain Website</a>
No trees were killed in the sending of this message. However a large number
of electrons were terribly inconvenienced.</font>
</pre>
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