> Here is the Eight-configured recording:
> http://www.hljod.blog.is/users/df/hljod/files/baejarlaekurinn_blumlein.mp=
3
> Then the AB-setup:
> http://www.hljod.blog.is/users/df/hljod/files/baejarlaekurinn_ab.mp3
Arnthor,
I gave these the Brinicombe test - listening with headphones and close
speakers. I needn't have looked at the file names as they were like chalk
and cheese for the stereo images. I'll try to explain why.
In one recording, I heard a clean stereo image where each part of the water=
noise was placed within the width of the image. In other words, the angle o=
f
each stream sound was reproduced at an equivalent angle in the stereo image=
.
The ratio of object width to stereo width was probably equivalent to a
camera fisheye lens. With sound however, you get an overlapping image from=
the rear of the fig-8 pair, but this doesn't seem to affect this recording=
as it sounds fine.
The other recording had a focussed centre point to the image but at angles=
to each side, left and right, it became more and more defocused, giving a
stereo effect, but without any clarity. I created a left minus right "S"
signal and this was louder than I would have expected for an accurate stere=
o
signal. Looking at the left and right waveforms, there was a lot in common=
between them. With a coincident fig-8 pair, there is only a common sound at=
the centre of the image.
Now for the theory.
A coincident fig-8 pair gives volume stereo which is split between the
channels according to the angle of each element of the sound object, ie.
each splash contributes a proportion to the left and right signal according=
to its position in the sound object.
A spaced omni pair gives almost identical sound in each channel except that=
there is a time delay between left and right or vice versa. This also gives=
a stereo effect, but only up to the point where the time delay is equivalen=
t
to 17cms path difference. Beyond this time difference, we stop hearing a
stereo effect and just hear an out of phase sound.
An out of phase effect is often used to create pseudo stereo, but it can
never give a clean stereo image. An example of this is added reverberation=
in music to give "space", but to my mind if this space sound is equal or
louder than the prime direct stereo sound, it reduces the overall stereo
effect.
The ideal stereo recording is a dummy head recording which has both volume=
and phase stereo, but if the dummy head doesn't match your own head, it
won't work 100%.
I'm less worried about low frequency differences between the recordings
because the 3-dimensional pickup areas are different, including echoes, but=
I would trust the fig-8 pair to be closer to the original sound object. Als=
o
when you start mixing out of phase signals, you get all sorts of frequency=
effects like "comb filter" effects. On a power spectrum there is a comb
effect starting at about 12Hz corresponding to an echo at about 7 metres
away.
Artificial out of phase reverberation is used extensively in music
recordings and this consists of time delayed sounds as also in mono which
has been "doctored" into stereo which keeps cloth-eared punters happy, but=
what the heck, stereo is an illusion after all - it's not real. :-)
David Brinicombe
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