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post #1 of 16 Old 08-04-2012, 07:17 PM - Thread Starter
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Hi,

Not sure this is the correct section for this question, but I hope so. I have some Blu-ray rips saved in .mkv files, with the DTS-Core extracted. I was curios to see how the waveform looks like for these DTS tracks, so I uncompressed them into wav/caf files and had a look at them in Audacity.

To my surprise, many of the DTS tracks I have checked have a lot of clipped samples. Is this normal? In other words, is it usual for the audio engineers to include clipped DTS tracks on Blu-ray's?

I am trying to figure out if something gone wrong during the ripping process or if they are just clipped from the beginning. It really varies depending on the movie, some are fine, some others are not. It seems the audio engineers do not follow any 'template' here.

Thanks for any opinions on this.
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post #2 of 16 Old 08-04-2012, 07:51 PM
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Be aware that dynamic range compression looks a lot like clipping. But in either case, sure they do it all the time. Either by boosting the gain and clipping the peaks, or by compression. Many movie tracks have enough dynamic range that if they lowered the gain to prevent clipping, most of the audio would be too soft. It may even be out of the control of the audio people who create the track, there's lots of people messing with it along the chain.
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post #3 of 16 Old 08-04-2012, 08:23 PM - Thread Starter
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Quote:
Originally Posted by rdgrimes View Post

Be aware that dynamic range compression looks a lot like clipping. But in either case, sure they do it all the time. Either by boosting the gain and clipping the peaks, or by compression. Many movie tracks have enough dynamic range that if they lowered the gain to prevent clipping, most of the audio would be too soft. It may even be out of the control of the audio people who create the track, there's lots of people messing with it along the chain.

Even so, it's rather amazing that the audio track is allowed to be severely clipped on a production Blu-ray. Makes you wonder what kind of rules they go by. Is it allowed to be clipped as long as it 'sounds' ok? Did they even listen to it?

I still feel unsure about this. I have heard that a few clipped samples is nothing to worry about, but I am seeing much more than a few samples.
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post #4 of 16 Old 08-05-2012, 05:50 AM
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There are no rules, they do pretty much what they want. Violating specs and just plain bad mastering are common.
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post #5 of 16 Old 08-06-2012, 12:27 PM
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How do you know it's 'severely clipped'?

Digital clipping is level > 0dBFS, which manifests visually as a 'flat top' peak between two samples. Having peaks (not plateaus) that come up to, but do not exceed, 0dBFS is not clipping. At low resolution , audio that has been 'maximized' the latter way may look clipped, but zooming in may
show that it's not.

Furthermore, just because there is clipping, does not necessarily mean it's audible clipping...even if it's much more than a few samples.

And finally, there are no concrete rules against it. There are DVDAs and SACDs* that have actual digital clipping , as well as plenty that are 'maximized' via dynamic range compresson. "High resolution" on the label is no guarantee that the audio is 'purist' or has a high dynamic range.


(The SACD 'rules' -- the Scarlet Book specifications -- do discourage extreme loudness, but there are ways around them)
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post #6 of 16 Old 08-07-2012, 05:53 AM - Thread Starter
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Quote:
Originally Posted by krabapple View Post

How do you know it's 'severely clipped'?
Digital clipping is level > 0dBFS, which manifests visually as a 'flat top' peak between two samples. Having peaks (not plateaus) that come up to, but do not exceed, 0dBFS is not clipping. At low resolution , audio that has been 'maximized' the latter way may look clipped, but zooming in may
show that it's not.
Furthermore, just because there is clipping, does not necessarily mean it's audible clipping...even if it's much more than a few samples.
And finally, there are no concrete rules against it. There are DVDAs and SACDs* that have actual digital clipping , as well as plenty that are 'maximized' via dynamic range compresson. "High resolution" on the label is no guarantee that the audio is 'purist' or has a high dynamic range.
(The SACD 'rules' -- the Scarlet Book specifications -- do discourage extreme loudness, but there are ways around them)

I looked at the waveform in Audacity. It has an option to show samples that are clipped (showing them in red). I didn't do any zooming since I trust Audacity here.

Having compared many DTS tracks from various Blu-rays now, I see no consistency. Some of them have a beautiful waveform, others just look rather terrible with clipping.
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post #7 of 16 Old 09-27-2012, 08:46 PM
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The question is how does Audacity define 'clipped'?

The good starting definition would be: two or more consecutive samples at 0 dBFS. That, however, would by no means guarantee that it was audible.

I have seen software that flags single samples at 0dBFS as 'clipping'. That software is dumb.

(It can also be dumb the other way: clipped audio might be lowered in level so NO samples reach 0dBFS. Dumb software will say there is no clipping, but there is. The smartest clip detection routine I know of is part of Wave Repair)
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post #8 of 16 Old 11-17-2012, 10:25 PM - Thread Starter
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Originally Posted by krabapple View Post

(It can also be dumb the other way: clipped audio might be lowered in level so NO samples reach 0dBFS. Dumb software will say there is no clipping, but there is.Wave Repair)

Not sure what you mean by "lowered in level". If I look at a pure waveform in Audacity without dynamic compression applied, and it shows clipping, then I think the audio is clipped and the damage is done. It doesn't matter if the audio levels are lowered after that.

I have never seen this problem on AC3 tracks. They are always much lower than 0 dBFS.

I think for DTS tracks the engineers do not care about DRC or DialNorm, or anything else, they just try to maximize the audio volume of the track, and if they do some clipping they might not care. But they should.
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post #9 of 16 Old 02-10-2015, 03:32 AM
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I'm facing this issue with DTS-HD MA tracks. The audio is clearly "clipped". The sound from my speakers and subwoofer is severely muffled during the clipped parts like some sort of overdrive "protection" has kicked in. Reducing the master volume has no effect, but reducing the player volume fixes the clipping completely. It's as if the full unclipped audio is restored. I don't understand how that's possible, unless the lowered output volume is somehow being used by the decoder stage. I'm using dtsdecoder.dll.

It implies that it's a decoder issue and the actual compressed data is not clipped.

I think the issue is due to incorrect 7.1 to 5.1 downmixing. The rear speakers as well as the crossover to the sub are causing clipping. Just like there's a specification for 5.1 to Stereo downmixing, there should be a specification for 7.1 to 5.1 downmixing.

Last edited by KurianOfBorg; 02-10-2015 at 03:41 AM.
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post #10 of 16 Old 02-10-2015, 05:00 AM
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My guess would be that the mixes are not being adjusted/checked for individual compression formats and software schemes.

Quote:
I have never seen this problem on AC3 tracks. They are always much lower than 0 dBFS.
I remember testing out DTS encoding software a few years back and how it produced a much "louder" file than the same master file fed into a Dolby Digital encoder. (Probably what helped make people believe the DTS versions sounded better?)

Similarly, the "Mastered for iTunes" tools frequently reveal to me how an otherwise fine mastered wav file may introduce clipping once processed through the AAC converter.

So I don't believe the problem is not always with the mixing or even mastering process (although sometimes it is), but perhaps studios are just not paying close attention to what happens to how particular encoding software is affecting their audio files.

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Reducing the master volume has no effect, but reducing the player volume fixes the clipping completely. It's as if the full unclipped audio is restored. I don't understand how that's possible, unless the lowered output volume is somehow being used by the decoder stage
Make sure your receiver's "compression" and/or "nighttime mode" feature is turned off. Leaving this on will make the music program sound like ass...

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post #11 of 16 Old 02-10-2015, 05:07 AM
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Quote:
Originally Posted by JeffPerrin View Post
Make sure your receiver's "compression" and/or "nighttime mode" feature is turned off. Leaving this on will make the music program sound like ass...
I'm running it as a pure analog power amp straight out of my PC. I should clarify that I'm decoding on the PC using LAVFilters and outputting analog.
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post #12 of 16 Old 02-10-2015, 11:03 AM
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Clipping on a short burst explosion is different than clipping on an acoustic guitar. You can get away with it if there's a big boom and rubble flying all over.
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post #13 of 16 Old 02-10-2015, 10:45 PM
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Clipping on a short burst explosion is different than clipping on an acoustic guitar. You can get away with it if there's a big boom and rubble flying all over.
The volume audibly reduces and the sound becomes muffled during these scenes.
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post #14 of 16 Old 02-11-2015, 05:07 AM
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Originally Posted by KurianOfBorg View Post
The volume audibly reduces and the sound becomes muffled during these scenes.
Yeah, that sounds like the effects of compression.

I'm on mac so I'm not familiar with LAV, but a quick Google tells me LAVFilters may have a DRC "Dynamic Range Compression" option for audio. Try turning this off.

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post #15 of 16 Old 02-11-2015, 05:10 AM
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Quote:
Originally Posted by JeffPerrin View Post
Yeah, that sounds like the effects of compression.

I'm on mac so I'm not familiar with LAV, but a quick Google tells me LAVFilters may have a DRC "Dynamic Range Compression" option for audio. Try turning this off.
DTS doesn't have DRC. Anyway, I narrowed it down to the subwoofer crossover. The subwoofer channel was getting clipped. Reducing the volume fixed it.
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post #16 of 16 Old 02-11-2015, 01:16 PM
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Glad you got it sorted out!

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