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Discussion Starter · #1 ·
I created a custom test with the DTS-HD Master Audio Suite to hear if I was having clipping with my Sony BDP-S490 2 channel output.

I made multiple 5.1 tracks and put a 0dBFS 500Hz sinewave in the Left channel for the 1st track, in the L and Center channel for the 2nd track and in the L, C and Left surround for the 3rd track.

I didn't embed any downmix, so that only the player would process its own downmix.

The sine in the Left plays fine, but when I switched to L and Center it sounded distorted, so there was already clipping. The L, C and Ls sounded with the same distortion but louder.

Then I made the same 3 tracks with my own donwmix with -7.5dB attenuation: no distortion in any combination.

That proved to me why I used to hear strange crisping when loud effects happened during movies or even just a character scream.
 

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You only proofed that that particular Sony has a bad downmix implementation. Other players might be fine.


It could also be that the downmix metadata was omitted in the test you created. (I do not know about the mastering suite you used, but I remember from DVDA mastering tools additional metadata could be entered to setup the downmix instructions like channel mapping and gain for the player.)
 

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Discussion Starter · #4 ·

Quote:
Originally Posted by Frank Derks  /t/1525489/do-not-use-blu-ray-playe...itable-with-multichannel-tracks#post_24559746


You only proofed that that particular Sony has a bad downmix implementation.

The Sony BDP-S490 follows Dolby's specs on downmixing for Stereo or Dolby Surround. The L & R are attenuated 3dB and the C by 6dB, but when played by both L & R, the C goes to +3dB above zero, thus clipped and distorted.
Quote:
Originally Posted by Frank Derks  /t/1525489/do-not-use-blu-ray-playe...itable-with-multichannel-tracks#post_24559746


It could also be that the downmix metadata was omitted in the test you created. (I do not know about the mastering suite you used, but I remember from DVDA mastering tools additional metadata could be entered to setup the downmix instructions like channel mapping and gain for the player.)

No the 1st test had no metadata, the player used the Dolby downmix and clipping occured. The second test has embedded metadata with my custom downmix and it's recognized by the player, because there's no more clipping/distortion.
 

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Quote:
Originally Posted by luca_frontino  /t/1525489/do-not-use-blu-ray-playe...itable-with-multichannel-tracks#post_24559795


The Sony BDP-S490 follows Dolby's specs on downmixing for Stereo or Dolby Surround. The L & R are attenuated 3dB and the C by 6dB, but when played by both L & R, the C goes to +3dB above zero, thus clipped and distorted.

..

It seems the Sony doesn't follow the Dolby spec. If it does the signals would not have clipped.

Make sense since you used a DTS HD audio suite!


The authoring suite might have the downmix gain settings at 0 db by default overriding the players default processing parameters. Did you check?
 

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Discussion Starter · #6 ·
Dolby's specs are wrong. To not clip a 5.1 to 2.0 downmix you must follow this process L & R untouched at zero, C at -6dB on both L & R (not -3dB, because it would play at +3dB above L & R), Ls & Rs at -3dB in each respective L & R. Then I calculated the gain of the sum of all channels: L @ 0dB + C @ -6dB = +3dB. L @ 0 dB + Ls @ -3dB = +4.5dB. Then I did 3dB + 4.5dB = 7.5dB, so I lowered all channels by 7.5dB. Result: L & R -7.5dB, C -13.5dB, Ls & Rs -10.5dB.

The default DTS Master Audio 2.0 downmix has exactly the gain of my player: L & R -3, C -6, Surr -6. And it clips.
 

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L & R untouched is wrong. L and R (and C too!) must be -3d to create headroom before adding content from the other channels.

The center channel is also -3dB down to create headroom and another -3dB to make up for the doubling due to the distribution across L & R.


Dolby's specs are ok.


But what have dolby specs to do with the decoding of DTS HD content?
 

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Quote:
Originally Posted by luca_frontino  /t/1525489/do-not-use-blu-ray-playe...itable-with-multichannel-tracks#post_24559944


Re-read my post.

Ok I did,

L & R untouched is wrong. L and R (and C too!) must be -3d to create headroom before adding content from the other channels.

The center channel is also -3dB down to create headroom and another -3dB to make up for the doubling due to the distribution across L & R.


Dolby's specs are ok.


But what have dolby specs to do with the decoding of DTS HD content?
 

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Discussion Starter · #10 ·
You clearly didn't read my post entirely. The final gains are: L & R -7.5dB, C -13.5dB, Surr -10.5dB. Now you'd ask why I used those values, but I already explained it in the post you didn't read entirely, so I won't waste any more time re-posting it.
 

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I understand what you did to fix the 'problem'. But imo it's wrong to compromise your mastering levels as a 'fix'.


Why do you refer to Dolby processing levels when you are using a DTS HD master audio suite? Your Sony is doing the DTS downmix wrong or is fed wrong metadata.
 

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Discussion Starter · #12 ·
I call it Dolby downmix because it is their standard. The S490 is not doing anything different than what Dolby and the DTS Suite default settings suggests as 2.0 downmix should be in their opinion. But I have found out that their downmix clips the loudest parts, that in movies are less noticeable because 2.0 users mistake them for noise actually present in the mix.

Why don't you people try it yourself, if you're so skeptical? It's a long process, I know, but if other users obtained the same results, I'd be right.
 

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Did you check another player? It may be the Sony that is messing up the down mix.


I do not have the DTS Audio suite so trying it out I can't do.


Normal mc content does not have the center channel content in left and right channel at 0dB. I think a better test would be LRC signals at -6db and check the players output levels for the downmix. It should stay at -6dB if not the player is doing things wrong.
 

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Discussion Starter · #14 ·
Again, the Sony is doing it "right" as-in it's following Dolby specifications, which are the same of the DTS MA Suite default 2.0 downmix. Testing another player would be pointless, but I'd like to test a receiver's downmixer, if I could afford one, because the signals above 0dB could still retain integrity in the digital domain of the receiver.


If for LCR you mean a 3.0 track, I already did a test with a pink noise on the C of a 3.0 track and the BDP-S490 downmixes it like a 5.1 without surrounds, so L & R -3dB and C -6dB, thus an LCR -6dB -6dB -6dB would be played at -9dB -6dB -9dB, because L & R are lowered by 3dB and the center is lowered to by 6dB down to -12dB but doubled by L & R, so regains 6dB and returns at original level. There's no clipping/distortion, but levels are uneven, exactly like it happens in Dolby's and DTS's 2.0 downmix specs.
 

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Quote:
Originally Posted by luca_frontino  /t/1525489/do-not-use-blu-ray-playe...itable-with-multichannel-tracks#post_24560933


Again, the Sony is doing it "right" as-in it's following Dolby specifications, which are the same of the DTS MA Suite default 2.0 downmix. Testing another player would be pointless, but I'd like to test a receiver's downmixer, if I could afford one, because the signals above 0dB could still retain integrity in the digital domain of the receiver.


If for LCR you mean a 3.0 track, I already did a test with a pink noise on the C of a 3.0 track and the BDP-S490 downmixes it like a 5.1 without surrounds, so L & R -3dB and C -6dB, thus an LCR -6dB -6dB -6dB would be played at -9dB -6dB -9dB, because L & R are lowered by 3dB and the center is lowered to by 6dB down to -12dB but doubled by L & R, so regains 6dB and returns at original level. There's no clipping/distortion, but levels are uneven, exactly like it happens in Dolby's and DTS's 2.0 downmix specs.

Yes I meant mc with content only in LCR, nothing in the rears, to check how it downmixes


What I don't understand is " thus an LCR -6dB -6dB -6dB would be played at -9dB -6dB -9dB" Is there still a signal in the center channel?

I suppose the downmix outputs 2 channel with levels back at -6dB -6dB.
 

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Discussion Starter · #18 ·
I miscalculated the doubling of the Center at the line level, when it actually happens at the speakers level. So, the following is what really happens in the Left channel (or Right) during a standard downmix: Left @ -3dB (0.707946 Volts) + Center @ -6dB (0.501187 Volts) + Left surround @ -6dB (0.501187 Volts) = 1.71032 Volts which corresponds to +4.661547dB over zero.

There is still clipping, it's just a more conservative +4.66 rather than my erroneous +7.5dB.


So, the correct downmix should be: L & R @ 0.45291 V (-6.879769dB) + C @ 0.226455 V (-12.900362dB) + Ls & Rs @ 0.320635 V (-6.879769dB -3dB = -9.879769dB) = 1 V = 0dB
 

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Discussion Starter · #19 ·
I made a new test, this time with multichannel LPCM with the -3dBFS 500Hz tone in the following channels:


Left of a 2.0

Left of a 5.1

L and Center of a 5.1

L, C and Left surround of a 5.1

Left of a 7.1

L and Center of a 7.1

L, C and Left surround side of a 7.1

L, C, Lss and Left surround rear of a 7.1


Clipping/distortion NEVER happens in any track!

I noticed that the stereo downmix is performed differently with LPCM than with DTS MA. The 5.1 is louder in DTS MA with the center matching in volume the single channel of a DTS MA 2.0 track and the L & R of the DTS MA 5.1 are lower in volume than the center. The DTS MA 7.1 is lower in volume than the DTS MA 5.1, but still higher than LPCM 7.1 and it clips.

In LPCM the L, C & R match in volume and the 5.1 & 7.1 also have the same volume for each respective channel, but they are definitely lower than the 2.0 LPCM.

I haven't had the time to take SPL measurements, but the player definitely has different downmixes for different codecs. Remember that my DTS MA tracks had no metadata in the 1st test where they clipped.
 

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I use an Oppo bdp95 and its' two channel output. It works just fine. That would seem to be a sony unique only problem.
 
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