Clipping in retail movies with DTS-HD tracks

[xerox44]

Hi everyone.

I've recently noticed some strange sound artefacts, coming from especially my rear-speakers, in some recent movies - those so far being 'the Equalizer' (eng DTS-HD track) and 'Edge of Tomorrow' (EU release, german DTS-HD track) - which I assume is actual 'clipping'.

Searching the internet, I found this topic that discussed similar findings in the movie Tron: Legacy on this very forum. I believe it is the same issue I am encountering:
http://forum.doom9.org/showthread.php?t=162030

Anyway, what I am experiencing in 'the Equalizer' (US release) can be found at precisely at 00:31:36 - when the first action scene unfolds and the whole sound effects increase in loudness until eventually something that is closest described to electric artefacts / popping is audible from the rear-speakers. It can be heard even at turned down volume.

This can only be heard when playing the DTS-HD track. If I disable HD audio, so that only the DTS-core track is passed-through to the amplifier, the artefacts / popping isn't there.


Trying to figure out if my set-up is causing this or if this indeed is clipping found within the audio-track of the BRD movie, I have attempted to extract the DTS-HD track using eac3to. While doing this, at precisely around 1/4th into the processing, eac3to outputs:

Clipping detected, a 2nd passs will be necessary.

I assume this pretty much confirms that the audio track is indeed clipped and that is what is causing the electronic "pop" artefacts from my rear-speakers?


Reading the Tron: Legacy topic I linked above, it seems some set-ups are more affected by clipping than others. For the record, I am using a Rotel surround processor in combination with a class-D amplifier. Could it be that a class-D amp would deal with clipping differently than say, an analog amplifier would? I know for a fact that a friend of mine with a class-B amp (but different amplifier brand) isn't hearing it - or may this be down to some surround processors / receivers using something like a clipping filter?

For the record; the artefacts that I heard in the EU version of "Edge of Tomorrow" were only present on the german DTS-HD audio track - the english DTS-HD track was unaffected. Is this just shoddy encoding by the "professionals"? Obviously, this topic concerns me, as the artefacts I'm hearing could potentially damage my speakers.

Anyone else with similar findings?

[Sparktank]

'the Equalizer' (US release) can be found at precisely at 00:31:36

That movie doesn't come out for retail sales for another week.
Edge of tomorrow I rented once and haven't bothered to purchase it.

There was some minor talk over the movie Oblivion (2013) where it seemed like certain parts were clipping in the center channel.

It seems it's an actual clipping issue in the mastering.
But the overall consensus is that most people dont' notice it.
This is either due to having different environments (different surround sound systems, different speakers, different Arcsoft codecs, different methods of decoding: lav+ffdshow, etc).
Most reviewers won't bring it up because it's masked by their very loud sound system (and probably something expensive).

In case of Tron: Legacy, it's easy to say it's a "digital" movie (having taken place inside a computer) and that any distortion is intentional, since Daft Punk was also involved with the music in the film.

It's an endless debate, but different decodes using different Arcsoft versions revealed there was clipping in the disc.

But, since MakeMKV works differently with Arcsoft, I still haven't tried a FLAC conversion using MakeMKV and compare results to eac3to.

I also still haven't gotten my 3D disc back to see if it's on both discs or not (2D & 3D; although I doubt the mixing would be different for both versions).

Also, if you use -progressnumbers, it'll show you the % of progress and then you can see precisely where it encounters clipping.
"precisely" loses its momentum when followed by "around". ;)

[xerox44]

Hi Sparktank,

Thanks for replying. I think I may have narrowed down in what might be causing the clipping / popping artefacts. Seems there used to be a bug in the way some DTS decoders decode DTS-HD MA streams that can result in the clipping / popping. I found various reports on the AVS forum dating back to roughly 2008 that showed that various audio equipment like Onkyo, Yamaha and others suffered from it.

This bug is also refered to as "the DTS Bomb".

Link(s):
http://www.avsforum.com/forum/149-blu-ray-players/1008620-warning-dts-masters-bitstreamed-yamaha-onkyo-integra-can-damage-speakers.html
http://www.highdefdigest.com/blog/dts-bomb-cars-2/

From what it seems to be, my receiver seems to exhibit this same problem. Sadly, I can also confirm that in some of the movies being listed in that thread as being effected by the DTS Bomb bug - at least Tron: Legacy exhibits the same electrical intereference as described in that topic on my system.

Still, the question remains why eac3to when re-encoding that audio track lists the exact same spot as "clipping detected". Is it actual clipping in the audio track that is causing mine as other receivers from 2008 to produce those artefacts?

Given that various people in that thread listed Tron: Legacy as also a candidate where this popping/clipping can be heard makes me wonder if this was also picked up on this forum in the above link I refered to in my first post. For the record, I tested the elevator scene (half way through the movie) which is where the popping can be heard.

PS: Thanks for the advice on the -progressnumbers command. It gives out that message at precisely the point where I have the sound artefact in the movie (but only the first occurance).

[Sparktank]

It's not limited to receivers only.

Remuxing Tron: Legacy and playing back on PC (no bit-stream; LAV Audio+Arcsoft to decode then to FFDSHow), will exhibit the ditortion.
I use cheap PC speakers, so it all gets downmixed to stereo. The clipping is still there.
Converting DTSHDMA to any other format, there's clipping.

When clipping is first detected, it won't report any extra instances of clipping.

I believe if you convert with eac3to to WAV and then use SoX, you should be able to get some comprehensive log files for how many times you come across clipping.
I haven't used SoX in a long time, so you'll have to do some searching/asking on that.

Another scene where there's a lot of noise distortion is where the the Flynn family (and Qorra) are fleeing the ship on their own flight craft heading towards the gate.
A lot of the chase scene exhibits distortion.

IIRC, in theaters some of the speakers blew out and the movie got quietter all of a sudden (in the middle of an action sequence). My brothers noticed, too.
I believe this movie was well known to blow speakers in theaters.

[Emulgator]

Just for checking I just demuxed Tron:Legacy using HD-DVD Stream Extractor decoding with dtsdecoderdll.dll 1.1.0.9 to .w64.
Sony SoundForge Pro 10 showed:
Indeed, the English DTS-MA 7.1 16-bit soundtrack has bad clipping throughout many places
for Channels 1,2,3 (3 being the worst) at a threshold well below 0dBFS, namely -1.999dBFS.
On the same disc the german DTS-MA 7.1 24-bit does better: only Channel 4 touches 0dBFS at 17 places, but not too hard.
Will countercheck if I didn't make a mistake and give some screenshots soon.
Doesn't look like a receiver chipset fault...

[Sparktank]

Oh man. 16 bit for 7.1?
No wonder it sounds really bad when I downmix to stereo (for those clipped scenes).

German 24bit, I might look into importing this.

I can't remember, was it (strange setup) too?
I should remux the 2D version (USA/CDN).

[Emulgator]

I have to repeat it when I got time.
I went two different ways and might be comparing pears to apples.
I used MakeMKV just playing around with lots of options and obtained a partially demuxed-only and partially decoded All-audio mkv.
From there I took the german track which was decoded within MakeMKV into a 24-bit flac, decoded this to .w64 and checked
Then the next day I tried something different, demuxed and decoded the (not-yet decoded within MakeMKV) english track
from the All-audio mkv, this time using HD-DVD Stream ectractor for decoding using eac3to into .w64
Might be that this second procedure left me with only 16bit while decoding within MakeMKV might have made 24 bit available.
One of MakeMKV's features is that it will obtain 24 bit audio from DTS-MA when dtsdecoderdll.dll is available.
If it does anyway, even if the source is only 16bit worth, I don't know.
Again, I will have to repeat this. Maybe this exhibits different results depending on decoder chain.

[xerox44]

It's not limited to receivers only.

Remuxing Tron: Legacy and playing back on PC (no bit-stream; LAV Audio+Arcsoft to decode then to FFDSHow), will exhibit the ditortion.
I use cheap PC speakers, so it all gets downmixed to stereo. The clipping is still there.
Converting DTSHDMA to any other format, there's clipping.

When clipping is first detected, it won't report any extra instances of clipping.

I believe if you convert with eac3to to WAV and then use SoX, you should be able to get some comprehensive log files for how many times you come across clipping.
I haven't used SoX in a long time, so you'll have to do some searching/asking on that.

Another scene where there's a lot of noise distortion is where the the Flynn family (and Qorra) are fleeing the ship on their own flight craft heading towards the gate.
A lot of the chase scene exhibits distortion.

IIRC, in theaters some of the speakers blew out and the movie got quietter all of a sudden (in the middle of an action sequence). My brothers noticed, too.
I believe this movie was well known to blow speakers in theaters.

Interesting stuff. I will definately have to try SoX and see if it shows up all the areas where I am experiencing the popping / audible crackling within the movie.

About the clipping or "distortion" - perhaps to be sure that we are talking about the same artefacts, I have made two recordings that demonstrate what I am hearing:

Example Edge of Tomorrow scene @ 00:34:32 - at 29 seconds (http://temp.conceptics.ch/01_edge_of_tomorrow_2014_EU_00_34_32.aac)
Example The Equalizer scene @ 00:31:37 - at 18 seconds (http://temp.conceptics.ch/02_the_equalizer_2014_US_00_31_37.aac)

This is precisely what artefacts my receiver / DTS decoder is producing. In the movie Tron: Legacy, the same crackling can be heard, although in that movie, it's harder to pick out because the rest of the movie is quite loud in those scenes. Are you guys refering to the same artefacts or just distortion in general?

Also Sparktank; Can you put down the exact timestamp of the clipping you are refering to in Tron? I will definately re-test and post back results.

As for what is causing the artefacts on my system - I assume it's actual clipping on the audio track that is not handled properly by my DTS decoder which then results in those artefacts. Perhaps different DTS decoder handle it different, so it sounds different, but I think the source of the issue is actually clipping within the recording.

Also, a friend was able to help me out as he owns the DTS encoder software. We took the Equalizer dtshd track - I converted it into mono WAV files and then re-encoded to DTS-HD MA again - but the end result, even if slightly different in size by a few bits still exhibits the crackling when played over my receiver (e.g. Clipping still present within the re-encoded DTS-HD MA track).

[Sparktank]

Is that a recording of your receiver using your cellular device?
The sample rate is limited to 22.05 KHz.

You can use mkvtoolnix to split it down to just the problematic part and use eac3to to demux it to get the dtshd elementary stream.
That would be more sufficient to examine.

[xerox44]

Yes, that's a recording using my mobile phone. I wanted to link a recording of what the artefacts actually sound like through my speakers, as I feel supplying the dts-hd track itself would only show perhaps the issue (clipping) on the track itself, but not necessarely how a dts-decoder like the one in my AVR would deal with it.

I have since been able to test this Bluray on different set-ups. Playing it on a recent Marantz model for instance, showed that not all receivers exhibit what I am hearing: On the Marantz, the recorded artefacts were not audible at all. So, despite the track perhaps exhibiting clipping, it seems not all receivers (dts-decoders) are vulnerable to it.

This I think would be in-line with the topic I linked above pointing to the AVS forum about the possible bitstream-bomb bug on some receivers. That's just my take on it...

[Bigmango]

There was some minor talk over the movie Oblivion (2013) where it seemed like certain parts were clipping in the center channel.



Yes, this problem was resolved for me after using movie players with updated ffmpeg versions. (I am also converting to FLAC, and the FLAC audio had the same issue).

I pinpointed the problem down to ffmpeg.

After I had this problem with Oblivion, since I am using software with newer ffmpeg versions I never had this problem again. Edge of Tomorrow and Tron play fine here, without any clipping.

[Emulgator]

Counterchecked my results regarding Tron:Legacy. They were correct.

The english 16bit 7.1 DTS-HD MA soundtrack clips hard at -2dBFS,
the german 24bit 7.1 DTS-HD HRA goes to 0dBFS, but only touches.

(P.S., and see below: This (german) was for the loudest CH 4, but SoundForge's Clip search and me were overlooking german CH 3,
which suffers from the same disease as the english sound track, only at variable thresholds..)

The decoder is not at fault here, it is the mastered signal.
I can hear it from my standalone (Panasonic DMP-BD80 with 8 separate audio outs) as well.

Depending on personal mixdown settings further distortion may occur.
Any mixdown of any 2 tracks into 1 with factors above 0,7 will cause further clipping.
Any Mixdown of any 4 tracks into 1 with factors above 0,5 will cause further clipping.

As promised, here the screenshots.

The first two show the english 7.1, (worst Channel 3 magnified)
the latter two show the german 7.1 (loudest Channel 4 magnified)

P.S. And I overlooked the clipping of german Channel 3...
The same clipping well below 0dBFS, only with varying thresholds,
where the mastering engineer moved faders after damage had already been done...

[Sparktank]

Makes me wonder if this was an accident in the mastering and then left as-is since it's a digital sci-fi and they thought "it fits the theme, let's leave it".

This clipping was observed in theaters, having the speakers blown out and it suddenly got quieter in the middle of the action near the end of the film.

If it was an accident, and since it's long over-due from initial retail release date of the BD's, I doubt Disney would express any interest in re-releasing the movie with properly mixed audio.
Usually, replacement discs are only provided in a very short window once the BD hits the retail shelves. After a certain time, there's nothing anyone can do (unless the numbers are extremely large).

Perhaps if Tron 3 gets made and released, the promotions will likely work a trilogy boxset. Which would be the next window to express disappointment in the audio mix.

[Ghitulescu]

That's the trouble of having two fora opened the same time. I posted into the wrong discussion.

When I heard this error for the first time, I thought it was an issue with tsmuxer and HD audio, as this was an issue back then.

Then I read a bit about it, and to my surprise, there were informations that decoding in the player would avoid this issue, while bitstreaming it (and letting the AVR do the decoding) would cause it. The reports that the distortions would be randomly distributed would point to the same direction.

However, lossless algorithms should be deterministic, like eg RAR or ZIP. So unless there is a design flaw in the math section of the DSP all of them should be identical.

Thus the question - did you also checked other software decoders and/or captured streams from HW ones? Just to pinpoint the issue...