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5th August 2024, 23:48 | #1 | Link |
I might be autistic...
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TrueHD is not ALWAYS 100% lossless...only 99.998%
At least not in DEE 5.2.1
Granted, it's only 467 samples @ only 5.5262 dB above the noise floor, but lossless should mean lossless, no? Steps to reproduce:
Code:
Differences found in compared tracks. Zero offset detected. Comparing: "Q:\-46h.flac" "Q:\-46h.thd_.flac" Compared 30846960 samples. Differences found: 467 values, 4:29.905000 - 6:59.012688, peak: 0.000000 (-138.47 dBFS) at 4:29.905000, 4ch Channel difference peaks: 0.000000 0.000000 0.000000 (-138.47 dBFS) 0.000000 (-138.47 dBFS) 0.000000 0.000000 File #1 peaks: 0.635144 (-3.94 dBFS) 0.631598 (-3.99 dBFS) 0.789073 (-2.06 dBFS) 1.000000 (0.00 dBFS) 0.394280 (-8.08 dBFS) 0.396389 (-8.04 dBFS) File #2 peaks: 0.635144 (-3.94 dBFS) 0.631598 (-3.99 dBFS) 0.789073 (-2.06 dBFS) 1.000000 (-0.00 dBFS) 0.394280 (-8.08 dBFS) 0.396389 (-8.04 dBFS) Detected offset as 0 samples. Total duration processed: 10:42.645 Time elapsed: 0:15.049 42.70x realtime The "Mix" pictured in the screenshots is the original LFE + the inverted THD LFE summed together and normalized to 0 dB. It looks like the center channel might have also had some differences but I neglected to check that one since the LFE channel caught my attention. I have yet to find any other sources where the same artifacts appear. For what it's worth, I've yet to encounter any sample where DTS-HD MAS, or any other lossless codec, doesn't produce bit-identical output*** ***Save for the 1024/16 samples prepended and appended to everything that comes out of MAS because of reasons. There's a chance this is something they have already fixed in a newer version of DEE, but, you know If you do have access to a newer version of the encoder and feel like testing this "killer sample" out, send me a PM. AFAIK the only settings that actually affect the audio data are <surround_3db_attenuation> (defaults to ON, I have it off) and <optimize_data_rate> (defaults to off anyways). You can set DRC/DialNorm/etc to whatever you want and it won't change what you get out of the other end from eac3to (ignores DRC by default) or ffmpeg (with -drc_scale 0) Last edited by tebasuna51; 11th August 2024 at 09:52. Reason: attachements already in postimg |
6th August 2024, 00:24 | #2 | Link |
Big Bit Savings Now !
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Well, first we abuse the LFE channel: feed non bandwith-limited signal to a LFE encoder, and at 0dBFS.
Then we find a difference, a flipping LSB worth. Then we use normalisation on that (a huge amplification under these circumstances). Then we analyse that boosted ping to find diracs. To be expected ? A comparison would be to drive a car against a wall, record that and...find it noisy. Lets see if Dolby revisits that use case.
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6th August 2024, 01:24 | #3 | Link | |||
I might be autistic...
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Quote:
Quote:
This isn't format fanboism, a lossless encoder should have zero killer samples, it is supposed to be lossless - I'm just reporting what I found... Quote:
I don't expect them to I think you've missed my point entirely and replied solely based on the thread title I chose... |
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6th August 2024, 06:08 | #4 | Link |
I might be autistic...
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Location: 16-235
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Here's a different example of it doing the same thing either across three channels or on the third channel (center, not LFE).
Code:
Differences found in compared tracks. Zero offset detected. Comparing: "Q:\E3.33\3.33_00011_MPLS_00002_M2TS_track2_jpn.flac" "Q:\E3.33\3.33_00011_MPLS_00002_M2TS_track2_jpn.thd" Compared 305088000 samples. Differences found: 6800 values, 13:00.342854 - 1:38:20.332583, peak: 0.000000 (-138.47 dBTP) at 13:00.342854, 3ch Channel difference peaks: 0.000000 (-138.47 dBTP) 0.000000 (-138.47 dBTP) 0.000000 (-138.47 dBTP) 0.000000 (-138.47 dBTP) 0.000000 (-138.47 dBTP) 0.000000 (-138.47 dBTP) File #1 peaks: 0.998749 (-0.01 dBTP) 0.999664 (-0.00 dBTP) 0.999969 (-0.00 dBTP) 0.973450 (-0.23 dBTP) 0.999969 (-0.00 dBTP) 0.999634 (-0.00 dBTP) File #2 peaks: 0.998749 (-0.01 dBTP) 0.999664 (-0.00 dBTP) 0.999969 (-0.00 dBTP) 0.973450 (-0.23 dBTP) 0.999969 (-0.00 dBTP) 0.999634 (-0.00 dBTP) Detected offset as 0 samples. Total duration processed: 1:45:56.000 Time elapsed: 3:56.332 26.89x realtime Doubly (heh) interesting is the fact that it coded anything there at all. The input was 16bit here, while it was actually 24bit input in the OP. Putting this THD file through eac3to doesn't show the usual message about a 2nd pass reducing the bit depth to 16 either: Code:
Original audio track: max 24 bits, average 16 bits, most common 16 bits. |
9th August 2024, 22:41 | #6 | Link |
SuperVirus
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Well, it does appear Dolby Inc. skrewed some things when it created TrueHD as a ""superset"" of Meridian's "packed PCM" (better known as M.L.P.). The use-case of MLP is «audiophile stuff», whereas the use-case of TrueHD is movies, so they apparently decided to "take some liberties" w.r.t. lossless compression :-|
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10th August 2024, 17:07 | #7 | Link |
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With movie soundtracks on an encrypted disc the copy is not supposed to be used for new encodings. So there is not any practical gain from them being strictly lossless. Could this be a minor problem with the open source decoder?
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12th August 2024, 08:44 | #8 | Link | |
SuperVirus
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Quote:
In summary, ReBit is a set of lossy parts ""surrounded"" (so to speak) by lossless compressed segments :-/ The reasoning for the existence of ReBit was/is the maximum bitrate allowed by the DVD-Forum specifications; but I don't know what would be the reasoning (or excuse) of Dolby for allowing TrueHD to include "lossy islands" in a lossless stream, since Blu-Ray discs are not DVDs. 0_o
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12th August 2024, 16:16 | #9 | Link | |
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Quote:
Movie studios market the term "lossless audio" for their Blu-Ray discs, but some movies have the Cinavia watermark added (which is by definition destructive to the original audio), and now we learn that TrueHD isn't lossless either. I guess there is always DTS-HD MA. Last edited by kurkosdr; 12th August 2024 at 21:16. |
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13th August 2024, 03:05 | #10 | Link |
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The sound is still overwhelmingly "HD" if it delivers 20..23 bits of resolution. On DVD, the bitrate would only reach high systained values during loud, noisy sections, when the ability to hear lower bits is diminished.
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13th August 2024, 03:36 | #11 | Link |
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There might be some factors.
1. Bitdepth reduction might be on in DEE/DME. 2. The way MLP/THD works the core of THD is stereo (IIRC stereo decoding is mandatory for HDDVD, but not surround) , and all surround is a reconstruction, so may produce low level errors. |
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bug, dee, killer sample, truehd |
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