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Sibelius multi-microphone recording

At 00:00 17/01/97 -0500, KImmoor@aol.com wrote:
>Lastly, I was
>listening to the GG Sibelius disc at the office on Tuesday, and it got me
>thinking about the recording technique of multiple perspectives that was
>employed for these pieces. (Stegemann's liner notes to this disc and the
>comparison he makes to Prokofiev's similar recording process are particularly
>pithy.) I would like the opinion of the more ardent audiophiles out there,
>just how successful was the recording as a new means of designing audio space
>and making "the image of the instrument most appropriate to the music of the
>moment." It certainly provides a new depth and lushness to Gould's
>performance, in light of his otherwise skeletal performing style, but at the
>bottom of it all, is it really anything more than a noisy reverb?

This is not really from an audiophile's point of view, but from a past
student of sonology (basically the theory of music recording and
technology).  There is a huge problem with this sort of multiple microphone
technique due to the basic physics of sound.  When any two, or more, sound
sources interfere with each other (ie are played in the same room) the
resultant overall sound is a combination of the spectra of the sounds
(spectra [pl.] The harmonic content of a sound source) where the peaks of
the spectra are added, and the troughs are subtracted (If anyone wants the
real nitty gritty techy stuff I am happy to answer).  This basically means
that some frequencies are enhanced, and some frequencies are attenuated,
often missing.  Now because this also happens to the reflections of sounds
in a natural environment, eg a room, the interactions become horribly
complicated and what happens in most situations is that the sounds mix
together in a nice way, with an inherent colouring of the sound from the
room dimensions and reflective surfaces. (Try moving objects around in a
room with a good cd player and separated speakers.  The effect can be stunning).
  In a recording situation, the microphones don't often pick up relections,
as well as usually being in a non-reflective environment.  This means that
the sound combinations are not diffused as they are in a reflective
environment and the attenuation/amplification problem is important.  The
situation is even worse  when working with a single sound source (eg the
piano in the Sibelius) because the different positions of the microphones
cause a change from the one source.  This effect is called a comb-filter, as
the sound pattern looks like a fine toothed comb and it can be heard in lots
of television studios when the speaker changes position and speaks into a
different microphone. Also, the studio/guitar effect called the phaser works
in a very similar way.
 The upshot of all this, is that when using a multi-microphone setup, and
time the perspective is changed (eg emphasising a particular microphone in
the mix) the comb-filter effect has an enormous effect, most of the time to
the detriment of the sound (the noisy reverb in the above quote).  For all
of those ppl with these cd, see if you can hear the changes in the sound
when the different mics are used.  Most of the time they are sectional ie
the mixing is done between sections, but I am sure that it also appears
Bruce Petherick                          |
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