But then I noticed that this would be suitable for headphones but not for speakers.
If you want a downmix for your home stereo I don't think you can do much better than simply mixing the surround channels to the front channels like this:Lt = FL + s*SL + c*CRt = FR + s*SR + c*Cwhere s (=surround mix) is usually something between 0.5 and 1and c (=center mix) is usually 0.7. This would be a "normal" stereo downmix.
How is the downmix done on a standalone dvd player. And is it possible to do something similar in software?
Quote from: robaer on 11 June, 2007, 04:39:47 PMHow is the downmix done on a standalone dvd player. And is it possible to do something similar in software?The audio stream in question probably has mixdown coef's contained somewhere in it. The processing shouldn't be hard once you know them.
Quote from: Woodinville on 11 June, 2007, 06:15:32 PMQuote from: robaer on 11 June, 2007, 04:39:47 PMHow is the downmix done on a standalone dvd player. And is it possible to do something similar in software?The audio stream in question probably has mixdown coef's contained somewhere in it. The processing shouldn't be hard once you know them.So it's done differently on each disc then? I've often wondered if it's downmixed with Dolby Pro Logic in mind or just plain stereo when using line out instead of spdif. Any info on this could be useful when doing your own downmixes.
Lo = 1.0 * L + clev * C + slev * Ls ;Ro = 1.0 * R + clev * C + slev * Rs ;
According to the AC-3 specification on atsc.org this is the way to downmix 5.1 to stereo:QuoteLo = 1.0 * L + clev * C + slev * Ls ;Ro = 1.0 * R + clev * C + slev * Rs ;clev (center level) and slev (surround level) are provided by the AC-3 file.That bring's up a new question for me: Until now I relied on the correctness of the AC-3 and DTS decoding plugins available for foobar2000. But these plugins don't do any downmixing. So, are clev and slev also used for decoding a 5.1 signal without downmixing to stereo? Because if they weren't there would be no way to use these values for downmixing afterwards.
So, clev and slev are only used for downmixing? In that case I would finally be able to do a proper downmix "by the book", at least if it's AC-3.
But what about DTS? I only found a rear channel attenuation setting in the encoder options (screenshot). What I don't know is if that's only a flag (that decoders must take into account) or if the rear channels are preprocessed so that it doesn't matter to the decoder anymore. And what are the "global" downmix rules for DTS if there are none embedded into each file?
Lo = 1.0 * L + 0.7071 * C + 1.0 * Ls;Ro = 1.0 * R + 0.7071 * C + 1.0 * Rs;
DTS isn't that open as Dolby wrt this, i.e. to my knowledge you won't find any detailed informationas in the ATSC-documents. So any information posted here would probably bring some troublefor the poster with it :-)
There's a publicly available technical documentation for DTS available here.Two passages caught my attention. Chapter 3.1.11 ("Stereo Down Mix") states that dynamic 2-channel downmixing coefficients can be embedded into the stream. Chapters 7.1.10 ("Embedded down mix flag") and 7.3.10 ("Stereo down mix coefficients") seem to specify that a bit further. It is strange however that I didn't find any options concerning this in the SurCode encoder and the screenshot of the official encoder. So maybe this was never used in any recording.
L = Lf + C/2 + LsR= Rf + C/2 + Rs