Hi,
I am once again doing some experiments decoding UHJ source material to
ITU standard domestic surround sound speaker layouts and re-encoding the
results into AC3. I keep seeing in the Ambisonic literature on the web
references to the use of shelf filters in the decoding process and the
comment that any filters "will be different if the B format being
decoded has been recovered from UHJ" to those used when decoding
"native" B format. The use of shelf filters (and other assorted tweaks)
seems to be recommended for smaller scale speaker layouts.
My current decoding workflow is as follows.
1. Recover B format from UHJ using convolvers and the impulse responses
provided by Angelo Farina.
2. Pass the recovered B format into Fons Adriaensen's Ambdec decoder
using his ITU speaker layout configs.
3. Encode the resulting speaker feed outputs into AC3 using "aften".
My questions are.
1. Should I experiment with shelf filters between steps 1 and 2, or does
the Ambdec decoder already do that internally (I saw a reference to it
doing this somewhere).
2. If the Ambdec decoder does this how should I configure it to account
for the original source material being UHJ?
3. If I should put an external filter in does anyone have any impulse
files that i could use?
The only document covering shelf filters I have come across is at
http://ambisonic.info/info/ricardo/shelfs.html but it is way beyond me.
However it the only place where I have found any reference to what a UHJ
filter should be (fig 3.3).
All help gratefully received!
Roger
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