> There's one point I don't think has been made explicitly. In
> analogue audio recording the occasional peak over 0dB was fine and
> even, in some cases, desirable.
Robin,
More explicit reply but not A rated :-).
Only with tape recording. When I started out, we were still using a
"sound camera" for optical recording, and that had a
compressor/limiter to prevent overloads. With gramophone recording,
too high a signal would cut into the next groove on the disc lathe,
but there was often a provision for widening the groove separation
ahead of peaks and the recorder also usually had an analogue limiter
in circuit as well.
With digital recording, one bit more than 15 will flip the polarity,
making peak distortion rather ruinous with a tearing sound. Almost all
digitisers now have a "hard limiter" which clips the level before it
hits the peak.
With tape recording, overload distortion is more acceptable as the
last few dBs get "compressed" in the tape head recording process, and
this was useful for deliberately distorting explosions and gunshots
(and even shouts). So much so that now kids all think that guns go
"kshew" and "gunshot generators", used for soundtrack laying,
synthesise this sound from a white noise source.
The Nagra IV series recorders had a pre-distort circuit which gave a
cleaner recording near the peak, but when they overloaded, they
clipped the peaks more audibly.
I have a major gripe with dubbed bangs as, even on news and hard
documentary material, bangs and gunshots are all brought into sync
with the picture whatever the distance. The silliest examples are
nuclear bomb explosions with a simultaneous dubbed-in bang. A-bombs
don't even make a bang, or at least a survivable bang. With the high
frequencies absorbed due to distance as with distant thunder, I
imagine you would hear a heavy rumble followed by a hurricane. You
might also hear a ground wave preceding any sound as with conventional
explosions. With thunder, they even remove the pre-strike static
crackle before the main strike which makes close thunder exciting.
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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