On Tue, Dec 13, 2011 at 09:31:27PM +0000, Roger James wrote: > My current decoding workflow is as follows. > > 1. Recover B format from UHJ using convolvers and the impulse responses > provided by Angelo Farina.
You could also use jconvolver / fconvolver. An UHJ decoder preset is provided. > 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). If you are using 'itu5.1-ord1-optim.ambdec', you have the equivalent of a decoder with shelf filters. The actual implementation is different, but the result is the same. > 2. If the Ambdec decoder does this how should I configure it to account > for the original source material being UHJ? I don't have any information as to what would be required. OTOH I suspect the differences will be small. Also any special 'UHJ' shelf filter, if you can find it, has probably been computed for some regular layout (e.g. a square). In this case the layout is irregular, and the shelf filters are already optimised for that layout. Just adding those for UHJ on a regular layout will not produced the correct result. The information you need is the *difference* between shelf filterers for standard B-format and those for UHJ. If you look in the preset file, there are two matrices defined, one for LF and one for HF. There are also 'order_gain' values for each matrix. Only the first two of these matter (the others are for higher order). The first is applied to the W column of the matrix (the first column), the second to X and Y (the second and third column). By changing these 'order_gain' values you can obtain the same effect as would be provided by additional or modified shelf filters. But I have no idea which changes would be optimal for a B-format input derived from UHJ. With the values defined in the preset you get a 'systematic' decode at LF, and one that hase been optimised for rE magnitude and direction accuracy at HF. Ciao, -- FA Vor uns liegt ein weites Tal, die Sonne scheint - ein Glitzerstrahl. _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
