On 30/05/2012 21:49, Eric Carmichel wrote:
So how good is Ambisonics in reproducing the original auditory 'scene'? If the
reconstructed wavefield is close to the original, then what happens when you
record the Ambisonics system itself? Will the playback of this recording yield
the same spatial information as the first recording did through an appropriate
first- or n-order system? Or will the recording of the playback capture the
so-called 'trickery,' thus making the recording-of-a-recording useless. Anybody
tried this? I think I’ll give it a go using a four speaker arrangement
(horizontal only) while playing a live recording of persons talking at eight
equally-spaced locations around a Soundfield mic. Upon playback, I’ll place the
Soundfield mic in the four-speaker arrangement, record this, and then listen to
the recording of the recording. How much localization info do you believe will
be lost? Could be fun, plus I’m a firm believer in learning by doing.
Hi Eric,
I have actually done this in the dim and distant past and I wasn't terribly happy with the
result, iirc. Thinking about it now, I realise that the main problem was probably caused by the fact
that it was a 'psychoacoustic compensated' decoder, with the shelf filters to move the decode from
velocity to energy decode at a few hundred hertz, where the mkI Human Head approaches half a
wavelength in size. It was also horizontal only.
So, the system would only reproduce correctly over two dimensions and below a few hundred hertz.
Above that it is not reproduced with exactitude - I think it was Jerome who showed this was
equivalent to changing the speed of sound - someone correct me if I'm wrong - which I think would
mean the correction in the Soundfield for capsule non-coincidence would be wrong. However, if a
simple velocity only 3-d decode is used together with a sufficient number speakers, the
reconstruction at the exact centre should be 'correct' with reducing degree of correctness as you
move away from the exact centre in a way that is frequency dependent. So, at the exact centre, it
should be picked up by the Soundfield as if it was the original sound field - at least up to the
point where the physical extent of the Soundfield mic array means the capsule sampling points are
outside the region of good reproduction.
Dave
--
These are my own views and may or may not be shared by my employer
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