Interesting.
Since the MP3 was created at a sample rate of 22,050 I don't think
that you are going to see anything above 11,025 hz. The clipping,
if anything, will most probably introduce harmonic distortion to
enhance the frequency content at an octave above the base. I agree
Dan, the clipping doesn't affect the quality that much since it it
filtered above 11kHz.
I looked at a spectrum analysis of the time during the clipping
(Sound Forge 6.0) and found a fairly flat response up to 11kHz.=20
Other parts of the file drop off at 8hKz.
I have several thoughts: 1) Had the MP3 file been created at a rate
of 44.1 kbs we would most likely see the frequency response up to
20kHz or so, 2) Perhaps the content of the sound produced by the
rotor blades kept the majority of the spectrum below 8khz anyway.
This whole issue got me wondering about the frequency response of
different MP3 quality settings. I took a thunderstorm clip that I
had made (essentially a great deal of broad spectrum sound) and
tried conversion at different quality settings; 64kbs - 128kbs. A
spectrum analysis of the results confirmed the response vs
conversion rates.
Any comments to this will be welcomed. I'm fairly new at all of
this digital sound processing. This forum has a wealth of
information and a great deal of experienced members. And, BTW
thanks Doug for introducing me to "naturerecordists".
Bill=20
--- In "evertveldhuis"
<> wrote:
> --- In Dan Dugan <>
wrote:
> > >That's an MP3 artifact. The .wav has no missing freqs.
> >
> > I've never seen anything like that, an octave band cut out. I'd
> > suggest a different MP3 encoder, unless it's happening on my
end. I
> > was playing it through the Pro Tools preview function, something
I
> > rarely use, because PT said there was an error and wouldn't load
it.
> >
> > -Dan Dugan
>
> Dan,
>
> I have downloaded the MP3 and converted with MPeg Suite 1.5 Then I
> loaded it in SoundForge 6.0 and took a look at the FFT (full
spectrum
> and level down to -150 dB); there was signal in that band, but is
was
> at all times much lower then the other bands. It might have
something
> to do with the massive clipping that occured in the piece, maybe
the
> WAV to MP3 coder had some kind of high freq band protection to
> minimize the audible clipping effects? After all, I looked at the
> waveshape, and inspite of the clipping 'seen' it wasn't to bad to
> listen to ; I have heard worse in my personal recordings :)
>
> Regards, Evert
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