{"action":"created","issue":{"url":"https://api.github.com/repos/Razzeee/xbmc-test/issues/24","repository_url":"https://api.github.com/repos/Razzeee/xbmc-test","labels_url":"https://api.github.com/repos/Razzeee/xbmc-test/issues/24/labels{/name}","comments_url":"https://api.github.com/repos/Razzeee/xbmc-test/issues/24/comments","events_url":"https://api.github.com/repos/Razzeee/xbmc-test/issues/24/events","html_url":"https://github.com/Razzeee/xbmc-test/issues/24","id":181913587,"number":24,"title":"AC3/DTS downmixed to Dolby Pro Logic II","user":{"login":"Razzeee","id":5943908,"avatar_url":"https://avatars.githubusercontent.com/u/5943908?v=3","gravatar_id":"","url":"https://api.github.com/users/Razzeee","html_url":"https://github.com/Razzeee","followers_url":"https://api.github.com/users/Razzeee/followers","following_url":"https://api.github.com/users/Razzeee/following{/other_user}","gists_url":"https://api.github.com/users/Razzeee/gists{/gist_id}","starred_url":"https://api.github.com/users/Razzeee/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/Razzeee/subscriptions","organizations_url":"https://api.github.com/users/Razzeee/orgs","repos_url":"https://api.github.com/users/Razzeee/repos","events_url":"https://api.github.com/users/Razzeee/events{/privacy}","received_events_url":"https://api.github.com/users/Razzeee/received_events","type":"User","site_admin":false},"labels":[{"url":"https://api.github.com/repos/Razzeee/xbmc-test/labels/P:%204%20-%20Normal","name":"P: 4 - Normal","color":"aa8888"},{"url":"https://api.github.com/repos/Razzeee/xbmc-test/labels/T:%20Feature%20Requests","name":"T: Feature Requests","color":"cccccc"}],"state":"closed","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":6,"created_at":"2016-10-09T21:38:19Z","updated_at":"2016-10-09T21:38:41Z","closed_at":"2016-10-09T21:38:20Z","body":"**Reported by Gamester17 on 3 Oct 2003 12:11 UTC**\n\nAC3 & DTS downmixed to Dolby Pro Logic II\n\nSo those without external AC3 or DTS decoder/amp an \nstill enjoy surround sound in Dolby Pro Logic II.\n\nDolby Pro Logic II downmix \nhttp://forum.doom9.org/showthread.php?\ns=&threadid=57988\n\nThe Dolby Pro Logic II downmix used in programs such as \nAzid.dll, BeSweet, HeadAc3he and AC3Filter, was derived \nin this thread: http://forum.doom9.org/showthread.php?\ns=&threadid=27936\n\nA test sample of 5 channels active one at a time, \ndownmixed to 2 channels with this matrix, should be able \nto be decoded by a Dolby Pro Logic II decoder back to \nthe original 5 channels. However, I have been \ndisappointed by the rear channel separation of the \ncurrent DPL2 downmix.\n\nThe rear channel separation can be improved by altering \nthe 'balance' of the surround channel downmix while \nmaintaining constant power. That is, BL is downmixed \nmore to Lt, while BR is downmixed more to Rt. However, \nby skewing the balance too much to either side, we lose \nphase information, resulting in reduced front-back \nseparation.\n\nHere I describe a method for deriving a better DPL2 \ndownmix\n\nMethods\nContents of 5.1 AC3 test source 'Avia ac3test' \nhttp://www.digital-\ndigest.com/dvd/downloads/trailers.html\n\n\ncode:-------------------------------------------------\n-------------------------------time (sec) channel \ncontents (announcer says: )\n12-14 L 'left front'\n14-16 C 'centre'\n16-18 R 'right front'\n18-20 BR 'right surround'\n20-22 BL 'left surround'\n22-24 L 'LFE'\nLFE [downmix\n\"C:\\tmp\\BeSweetv1.5b19\\BeSweet.exe\" -core( -\ninput \"c:\\tmp\\ac3test.DELAY 0ms.ac3\" -\noutput \"c:\\tmp\\ac3test.surround2.wav\" -2ch -\nlogfilea \"C:\\tmp\\BeSweetv1.5b19\\BeSweet.log\" ) -azid( -\ns surround2 -L -3db )\n\n'4.8 dB' downmix\nUsing AC3Filter in GraphEdit. Exact values of surround \ndownmix coefficients are SQRT(3/4) and SQRT(1/4). The \nsurround power difference is triple, hence 4.8 dB\n\nLt = L + 0.7071 C + 0.7071 LFE - 0.866 BL - 0.5 BR\nRt = R + 0.7071 C + 0.7071 LFE + 0.5 BL + 0.866 BR\n\n'6 dB' downmix\nLt = L + 0.7071 C + 0.7071 LFE - 0.8944 BL - 0.4472 BR\nRt = R + 0.7071 C + 0.7071 LFE + 0.4472 BL + 0.8944 BR\n\n\nDPL2 decoding as per thread: \nhttp://forum.doom9.org/showthread.php?\ns=&threadid=57736\n\nNotation of decoded channels: L' R' C' LFE' BL' BR'\n\nScreenshots taken from Cool Edit Pro\n\nSeparation between channels calculated from difference \nin total RMS power of 2 sec segments\n\nResults\nFigures at http://www.geocities.com/bleo98\n\nFigure 1: surround2 BL'\n18-20 sec, BR leaks into BL'. Separation ~ 9 dB\n\nFigure 2: 4.8 dB BL'\n18-20 sec, more separation between BL' and BR' ~ 26 dB\n\nFigure 3: 6 dB BL'\n18-20 sec, even more separation between BL' and BR' ~ \n31 dB\n\nFigure 4: 6 dB L'\nBUT! 20-22 sec, BL leaks into L'!\n\nFigure 5: 4.8 dB L'\n20-22 sec, no leakage of BL into L'\n\nDiscussion\nThe 4.8 dB downmix provides optimal separation of all 5 \nchannels. I now use this matrix in AC3Filter, but should \nthe azid.dll matrix be changed?\n\nsurround2 is quieter because the downmix coefficients \nwere normalised to prevent arithmetic overload. The 4.8 \ndB and 6 dB coefficients are not normalised. Overload \nwould only occur if all 6 channels were at full scale \nduring EXACTLY the same time sample, which is highly \nunlikely. In fact, this did not occur during testing with \nthe Lord of the Rings soundtrack.\n\nThe 'pulses' every two seconds are steering artifacts: a \ndelay in steering inherent in the decoder's feedback \ndesign (?)\n\nDPL2 cannot steer 5 independent channels \nsimultaneously. For example, during 22-24 sec, L \ncontains 'LFE' and LFE contains [rumble](rumble]----------\n-------------------------------------------------------\n---------------\n\n'surround2'). Note, LFE is \nsupposed to be decoded to C'. However, DPL2 steers \nBOTH to L' AND C' \n\n\nMigrated-From: http://trac.kodi.tv/ticket/10"},"comment":{"url":"https://api.github.com/repos/Razzeee/xbmc-test/issues/comments/252514550","html_url":"https://github.com/Razzeee/xbmc-test/issues/24#issuecomment-252514550","issue_url":"https://api.github.com/repos/Razzeee/xbmc-test/issues/24","id":252514550,"user":{"login":"Razzeee","id":5943908,"avatar_url":"https://avatars.githubusercontent.com/u/5943908?v=3","gravatar_id":"","url":"https://api.github.com/users/Razzeee","html_url":"https://github.com/Razzeee","followers_url":"https://api.github.com/users/Razzeee/followers","following_url":"https://api.github.com/users/Razzeee/following{/other_user}","gists_url":"https://api.github.com/users/Razzeee/gists{/gist_id}","starred_url":"https://api.github.com/users/Razzeee/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/Razzeee/subscriptions","organizations_url":"https://api.github.com/users/Razzeee/orgs","repos_url":"https://api.github.com/users/Razzeee/repos","events_url":"https://api.github.com/users/Razzeee/events{/privacy}","received_events_url":"https://api.github.com/users/Razzeee/received_events","type":"User","site_admin":false},"created_at":"2016-10-09T21:38:41Z","updated_at":"2016-10-09T21:38:41Z","body":"**Modified by vdrfan on 6 Feb 2011 17:27 UTC**"}}
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