[sdiy] Analyzing a Waveform

[Glen]

At 04:28 AM 6/2/03 , Fredrik Carlqvist wrote:

>Thunder blasts are fairly loud, at least when nearby, and with a
>powerful low-register content. So it should easily overdrive a simple
>microphone.

In my particular case, it was from the sound card. First, I moved the
microphone inside my room, and connected it with a much shorter cord. I
connected a scope to the output of my pre-amp and watched the waveform, as
I hummed into the microphone. I also watched the display of my wave
recording software, as I recorded the whole thing.

There was a certain point in volume where neither the pre-amp nor the
microphone was clipping, but my recording definitely was. The funny thing
was, my recordings peaked about 15 dB below the maximum value allowed by
the WAV format. It also had that sloped-clipping effect, which I have come
to believe is probably due to capacitive coupling.

It seems that my pre-amp had much more headroom than the input of my sound
card. Darn,  amateur-grade, non-standard,  so-called "line-level" sound
card input---why can't common sound cards be built to accept healthy signal
levels without clipping?

Anyway I increased the recording level in Window mixer, to make the WAV
file clip just before the point that my sound card input circuitry clips.
Now I can rest assured that if the recording meter in my software says
"0dB" or less, I won't be clipping the input.

Oh, the microphone also happens to be an instrument microphone, designed
for loud sound sources. I won't say that extremely loud thunder can't make
the microphone clip, but it would take a very loud and local thunderclap to
make it happen. If the lightning is that close, I probably have other
things to worry about.   :)

I want to thank everyone for all their suggestions with this. This is a
great list.


later,
Glen Berry