> 2. If the above will result in clipping of the loudest parts, what
> should I do about them? Audacity has a Compress function which looks
> like it might help bring them down a little without affecting the
> quieter parts.
Peter,
Further to what I wrote before, the Audacity compressor/limiter
automatically brings *up* the general level by the amount of
compression, including the noise.
You can do the opposite - using an expander and the Audacity "Noise
Removal" does more or less that, but get it wrong and it messes up a
recording. I use this for HF hiss, filtering out the lower frequencies
before taking the NR sample. (put them back with Ctrl Z)
If anyone is brave enough to edit the Audacity Equalization curves
(take a backup first), I've got profiles on:
www.stowford.org/sounds/eqcurvesadd.txt
The hiss reduction sample filter is: HPF4000-3-6-9hiss
> Should I pick a typical piece and adjust till its peaks are at some
> particular level?
What I omitted to say was that you should normalize the track before
doing any compression. Normalizing automatically finds the peak and
adjusts the whole level to make this peak -3dB or -6dB or whatever you
set. Only then do you know what levels you are compressing.
You can adjust the overall level by ear. First listen to the
background noise/hiss/rumble and put that at a level which you think
is not intrusive. If the bird, etc, is then not loud enough, then you
have a weak recording.
With filtering using "Equalization" you can reduce the bass background
by 6dB or maximum 9dB, but if the noise is still intrusive, it will be
forever a noisy recording. Get this right and you will be an expert.
:-)
Start off aiming at 30dB between noise and peak and then try to
improve it. With my woodland, I set wind, etc, noise at about -48dB
and wait for calls at or above -18dB.
Here's a very rough profile for a woodland dawn chorus as seen on
"Waveform (dB)" display:
Peak close birds -18dB or over
General dawn chorus hubbub -30dB
Atmosphere and reverberation -40dB
Noise hopefully under -48dB
I'm waitng for someone to disagree, but note the words "very rough".
:-)
Unless you have a clean recording, compression is a no-no as others
have said. An exception is something loud like thunder or a close
pheasant crowing near the mic which uses up your spare "headroom"
between your normal peak setting and 100% (up to 18dB or 3 bits), when
you can risk using limiting or compression.
Have a listen to various wildlife recordings on Soundcloud and
download some to see what the noise to peak level ratio is. That's
something to aim at but don't be discouraged - people tend to post
their best.
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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