I think I would prefer to do the noise reduction on the B format, rather
than the original A format, as it's a bit more robust to small gain/phase
errors. Although it's often useful to do a B-to-A conversion, process then
go back using the ATK, I can't see any advantage in this case.
There's been some good discussions of workflow in response to your question
so far and and I'm not going to recommend any, just whatever you feel
comfortable with. The only thing I can say is that if you're worried about
it you just (!) need to listen carefully to each to see if one is, in fact,
better (or worse) than the others, maybe using some specifically recorded
material (single voices, low and high frequency percussion and so on).
Anyway, have fun
Dave
On 4 January 2016 at 20:17, Trond Lossius <trond.loss...@bek.no> wrote:
> Hi,
>
> I’ve done some ambisonic recordings of ambience in very quiet environments
> using the SoundField SPS200 mic and a SoundDevice 788T recorder. The
> resulting recordings are A-format, and I use the SoundField SPS200 plugin
> to convert the A-format recordings to B-format. The resulting recordings
> have a bit of hiss that I suspect come from the recorder. The sound is very
> similar to recordings done using the 788T with no mic connected, and with
> the same recording levels as when doing the ambience recordings. I’d like
> to use Isotope RX4 to reduce the amount of hiss, and I’m wondering what
> would be best practise when dealing with 4-channel A- and B-format signals.
>
> RX4 is not able to deal with multichannel files, so I’l have to split the
> 4-channel recording into two stereo tracks, do noise cancellation on them,
> and then merge back into four channels again. However I can envisage three
> different approaches to this:
>
> 1) I treat the original A-format recordings, and afterwards I convert the
> processed files to B-format using the SPS200 plug.
>
> 2) I treat the converted B-format recordings.
>
> 3) I decode the B-format files to A-format using the BtoA decoder from
> Ambisonic Toolkit, remove noise, merge, and then reencode to B-format using
> the ATK AtoB encoder.
>
> I’m sure the first option will be the best when considering noise
> reduction only, as it reduce hiss before the four channels gets mixed. At
> the same time I’m concerned that it might offset phase information between
> channels, and hence interfere with how the SPS200 plugin compensates for
> distance between the mic capsules. For the same reason I’m thinking that
> processing of the B-format signal might interfere with phase information
> between the four channels and hence distort the spatial information.
>
> Do anyone else have any experience with this, and have a recommendation
> for what workflow leads to the best results?
>
>
> Thanks,
> Trond
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--
As of 1st October 2012, I have retired from the University.
These are my own views and may or may not be shared by the University
Dave Malham
Honorary Fellow, Department of Music
The University of York
York YO10 5DD
UK
'Ambisonics - Component Imaging for Audio'
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