I have little technical knowledge of electronics, and therefore delete
unread most discussion of such matters. However, many years ago, Walter
Knapp helped me greatly with my recording problems and I sometimes read a
message just because I see it's from Walter, and therefore know that not
only will it will contain sound advice, but will be expressed in terms that
even I can understand. So if what I am now about to write has already been
said in messages I haven't read, I apologise.
In a message on 22 Feb 2008 Walter wrote:
> Environmental noise like this is a huge problem. One airliner anywhere
> above the horizon can ruin a recording. Same with trucks miles away and
> so on. For most beginners in nature recording this is the biggest
> surprise, just how much noise there is. Our ears are very good at
> singling out the sounds we want, mics make no such distinction.
May I add to that.
As no doubt I learnt from Walter, the higher the frequency of a sound, the
more rapidly it attenuates with distance. Thus the noise we hear from
trucks miles away, or a commercial jet at cruising altitude, is mostly
low-frequency noise, well below the lowest frequency of the songs of most
birds. And it can therefore be filtered out of a recording using modern
computer software.
For example, if the noise is below 500 Hz and your bird song is all above
800 Hz, you can filter out all sound below 500 Hz, and the noise is gone
while your bird song is unaffected.
For making a sonagram, or otherwise analysing the song, that's fine. But
with all sound below 500 Hz removed, the recording may sound somewhat
unnatural, if you want it mainly for pleasant listening. But all is not
lost. Computer software to the rescue again.
Find a quiet section of your recording, where there is no noise and no bird
song for a few seconds. Copy this. Filter out all sound ABOVE 500 Hz.
Then copy and paste and repeat until you have a < 500Hz sound file as long,
(or a bit longer) than the recording from which you have removed the noise.
Mix the two together, and you've got a natural-sounding recording without
the noise.
I must leave it to you Nat/rec experts to advise on the software to do this=
.
Syd Curtis (Australia)
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