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Re: Bottoming-out revisited

Subject: Re: Bottoming-out revisited
From: "Eric Benjamin" <>
Date: Sat, 21 Jan 2006 22:25:55 -0800
John,

The information you gave is pretty helpful, especially the picture of the
distorted waveforms.  The waveform you got is what happens when analog
clipping occurs before a coupling capacitor.  The waveform goes up until
clipping occurs and then the coupling capacitor discharges exponentially.
The exponential decay is the big rounded scoop cut out of each cycle.

There is something else interesting about your waveforms.  You have eight
cycles and about .65 seconds, so the fundamental frequency is about 12 Hz.=

You described the sound as a "thunderous resonance" and that seems about
right.  For some reason people regard sounds below 20 Hz as inaudible, but=

that's simply not true.  The threshold of hearing at 20 Hz is about 76 dB
SPL (for us humans, that is) and threshold at 10 Hz is about 88 dB SPL.  So=

when the level is high those low frequency sounds are quite audible.  But
perhaps not quite as loud to the ear as they are high in level to the
microphone.  I believe that the analog preamp in your recorder is clipping.=

Some preamps clip at a certain level no matter how far down you turn the
gain.  It's also conceviable that the microphone itself is clipping, but
that probably would have been asymmetrical.

Your waterfall recordings are pretty great.  The problems are similar to
what I'm trying to do; make recordings of surf while I'm IN the surf.

Eric Benjamin




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