Audio Clipping - is 5.1 to Stereo conversion the issue?

[Silver Screen Samurai]

Hey, guys!
It's the Silver Screen Samurai.

UPDATE (for those interested) - scroll down if you just want the actual question:
Sorry I haven't posted in a while, personal life and everything. I'm posting this because, after a rather long break, I'm continuing work on a fanedit of "The Wolverine" that I began making 4 years ago. I made most of the major decisions back then, so this effort will be more like recreating that version; rather than starting from scratch.

Some of you may remember some earlier posts related to that project. I mentioned back then that I'm editing on a Mac using Davinci Resolve -- a free software, that is one of the most highly regarded professional softwares in feature filmmaking. It can mix audio, edit footage, and most importantly it's BY FAR the best color correction software available -- on top of which I mentioned struggling to find a means of converting MKV to a lossless Codec (such as ProRes) with Mac tools.

Yes, laugh if you want, but I also work in professional post-production. Mac computers are fast becoming the predominant ones in the industry, due to tools like Resolve and Black Magic tech. The only area they really suck is converting MKV to ProRes, but then again the post-production pipeline was never designed with the intent of ripping MKVs from discs (as opposed to just having the raw video files in the first place). I still haven't quite figured that one out, so for now I'm making the edit predominantly with a 3GB MP4 conversion from Handbrake; though I'll probably go back and switch it out with a ProRes, before release (using the timecode). This is standard procedure with professional post-production as it is; since they often edit with lower quality files before switching them out with ProRes, to save RAM.

Since I realize faneditors don't typically use Macs, I guess that means I'm possibly entering uncharted territory (no hubris intended in that statement, I swear on my life). Even fewer faneditors, as far as I'm aware, use Davinci Resolve. So I'd be happy, when the process is all said and done, to create some kind of breakdown for Mac editing with Davinci Resolve once the cut is completed.

THE ACTUAL QUESTION STARTS HERE - Everything up to this point has just been an update since last posting:
So using tsMuxerGUI, I was able to rip all of the audio files on the disc. This includes a 7.1 Mix, 5.1 Mix, Stereo Mix, and Director's commentary track. All of these came out as AC3s. Deciding to make the first pass of the edit with the stereo track, then go back and match it with the 5.1 and (maybe) 7.1, I split it into mono WAVs with Audacity. The problem is, when imported into Resolve, these appear to result in the audio clipping at certain places. It wasn't something I did, because this is also the case with the original AC3 file.

My guess is that it's probably a Blu-Ray issue. For those who don't know, films mixed in 5.1 Theatre surround sound are usually put on a Blu-Ray without actually being mixed for home viewing. Essentially you're getting audio mixed for theatre speakers playing on lower quality stereo speakers. This results in a lot of films not having a custom made stereo track for home viewing, and simply downscaling a 5.1 to stereo without any additional mixing. So it's not uncommon for Blu-Rays to be straight-up clipping when played in stereo, if they were originally mixed in 5.1 surround sound (but if you have any other theories, feel empowered to leave them below).

I'm sorry if I answered my own question, but what do you guys think? Should I solely release it in a 5.1 mix, or do fanedit enthusiasts prefer to have a 2-track Stereo mix? At the very least, a 5.1 Mix is possible in Davinci Resolve (didn't I say it was great?), and I suspect wouldn't read as clipping in the meters. It's entirely possible that the clipping issue would probably still occur when PLAYED on a stereo TV, but nothing a simple volume adjustment couldn't fix.

Regardless, thank you to everyone who takes the time to read this; It's greatly appreciated.

 

[M4_]

Personally I would not bother with stereo audio, both before editing and after editing when making encoding your final mixes. Devices and media players these days are all capable playing 5.1 audio through a stereo setup if a viewer does not have a surround sound. Though, for complicated sequences I always check the audio mix on headphones, stereo speakers, and an actual 5.1 set up to make sure the volumes sound about right for all types of viewers. A lot of fan edit viewers probably watch on stereo speakers or headphones, and I've only released 5.1 audio with no complaints

One thing I'd double check though is if the original audio tracks were in AC3, or if they were .thd or .dtshd and you've transcoded them to AC3. If the movie is older and only has AC3 by default then nevermind

 

[robulon]

Looks like we're both using the same Resolve on Mac setup. I'm not too sure about the audio clipping issue. It's not something I've personally come across. I've been mostly working with 80s films so far. Since their original sound mixes tend to have been stereo, any freshly remixed 5.1 on the Blu-Rays are fairly front centric compared to modern films. So there is never as much overall volume from all the channels playing at once.

I do have a solution to deal with MKVs though. Avidemux is available for Macs and you can use it to demux the MKV to a MP4. This extracts the H264 stream and just copies it into a MP4 wrapper. There is no re-encoding involved. From there you can just use Resolve to transcode it to a ProRes.

One thing to be aware of when you're using Avidemux's MP4 Muxer - there is a setting called Optimize for Streaming. You need to set this to "Move Index to the beginning of the file" before you export the new MP4. This option shifts the timebase to where it needs to be for MP4s (which is different to MKVs apparently). If you don't do this then Resolve won't be able to detect that the frame rate is supposed to be a constant 23.976 and you'll get dropped frames on playback.

 

[krausfadr]

Since Resolve will easily import and let you edit in 5.1 surround as one “track” there’s no reason to import this in stereo. I’d recommend ripping the DTS to WAV (DTS 7.1 to WAV 5.1) . Then if the WAV is more than 4GB, splitting that into two WAV files so Resolve will read them properly.

 

[Silver Screen Samurai]

I do have a solution to deal with MKVs though. Avidemux is available for Macs and you can use it to demux the MKV to a MP4. This extracts the H264 stream and just copies it into a MP4 wrapper. There is no re-encoding involved. From there you can just use Resolve to transcode it to a ProRes.

Thank you so much for this, Robulon. I tried using Handbrake for the workprint MP4, but that produces a ton of quality loss/bitrate reduction.
I'll absolutely be checking this software out.

One thing I'd double check though is if the original audio tracks were in AC3, or if they were .thd or .dtshd and you've transcoded them to AC3. If the movie is older and only has AC3 by default then nevermind

I'm starting to think the actual problem potentially might be tsMuxerGUI.
When using Handbrake to produce the workprint, the sound wasn't clipping anywhere near as much as when the same stereo track was exported to AC3 by tsMuxerGUI. I could go back and try it again, but my recollection was that that software didn't give a lot of options as to the output format of sound. I certainly won't be using it to get a ProRes, since it only allows me to transcode MKV to a Unix file for some reason; which obviously can't be edited.

 

[Silver Screen Samurai]

Since Resolve will easily import and let you edit in 5.1 surround as one “track” there’s no reason to import this in stereo. I’d recommend ripping the DTS to WAV (DTS 7.1 to WAV 5.1) . Then if the WAV is more than 4GB, splitting that into two WAV files so Resolve will read them properly.

Okay, thanks for this. Sounds like splitting 5.1 into WAVs is a similar principle to splitting stereo into WAVs then. I'll probably try doing that with Audacity.

Resolve oddly enough wouldn't let me import the 5.1 Track, but this again might be a problem tsMuxerGUI is creating (since, like the stereo track, it automatically converted them to AC3). Nothing Audacity shouldn't be able to fix but, based on what I said to @M4_ in my previous reply, it potentially might be clipping more than it should. I suppose I'll treat this run at importing the files like troubleshooting but, if the 5.1 isn't clipping in resolve as WAVs, I'll probably assume my original hypothesis about a downscaled Blu-Ray was right.

 

[TM2YC]

I've had a 7.1 to 5.1 problem recently. In 'HD Streams Extractor' I thought you added "-down6" in the Options box and output to wavs. It gives me a 5.1 mix (in 6 wavs) but the levels are all blown out on the loud bits. It being a war movie, they are clipping a lot. Multiple sources seem to say this is the right method.

The source is 'DTS Master Audio, English, 7.1 channels, 24bits, 48kHz'.

I'm going to try "-3dB -down6" and see what happens. Any other suggestions?

 

[Silver Screen Samurai]

I've had a 7.1 to 5.1 problem recently. In 'HD Streams Extractor' I thought you added "-down6" in the Options box and output to wavs. It gives me a 5.1 mix (in 6 wavs) but the levels are all blown out on the loud bits. It being a war movie, they are clipping a lot. Multiple sources seem to say this is the right method.

The source is 'DTS Master Audio, English, 7.1 channels, 24bits, 48kHz'.

I'm going to try "-3dB -down6" and see what happens. Any other suggestions?

Okay, THIS IS INTERESTING!
So this isn't just me then, it's a re-occurring phenomenon?

I found, when working with the stereo track, lowering the master volume to -5db eliminated the clipping. This was after locating the loudest peak in the film, and it did the trick. Granted, this is a stereo track being encoded to AC3 in tsMuxerGUI then transcoded to WAV in Audacity, which is different than what you're talking about, but it might be a related problem; might be worth a look.

(also, thank you for creating the "Hard Forged Edition" fanedit, it's one of my favorite ones ever made)

 

[Silver Screen Samurai]

@TM2YC hey, I corrected the previous comment; lowered the master volume 5 db, not 10... since that would obviously be way too much, lol

 

[TM2YC]

Lowering the volume just made everything quieter, the peaks were still clipped.

I tried just extracting the 7.1 mix to wavs and it's still clipped, so it's not the "-down6" mixing. It's either clipped on the original blu-ray (seems unlikely), or 'HD Streams Extractor' has a setting wrong somewhere that I don't understand, so is extracting the 'DTS Master Audio' wrong.

I mixed it down to stereo instead ("-down2") and that seemed to be fine with no visual clipping and seemed to sound okay. Hmmmmm.

 

[Silver Screen Samurai]

Lowering the volume just made everything quieter, the peaks were still clipped.

I tried just extracting the 7.1 mix to wavs and it's still clipped, so it's not the "-down6" mixing. It's either clipped on the original blu-ray (seems unlikely), or 'HD Streams Extractor' has a setting wrong somewhere that I don't understand, so is extracting the 'DTS Master Audio' wrong.

I mixed it down to stereo instead ("-down2") and that seemed to be fine with no visual clipping and seemed to sound okay. Hmmmmm.

Okay, it sounds like this solution only works for stereo mixing. It's starting to sound like this is actually a general common problem with Demuxing softwares and 5.1 Mixes; I think it's that they're probably designed predominantly for Stereo mixes, and so they aren't as retrofitted for 5.1 and don't allow for a lot of wiggle room for different encoding settings (at least tsMuxerGUI doesn't). A bit of a snag, but a good discovery for future reference nonetheless.

As a professional post-production editor, who has had to study up on blu-ray specs, I can confirm you're right that there's almost no way that the original 5.1 Mix was clipping on the Blu-Ray; that is to say it probably does clip when played on stereo TV sets, but in an editing software made for 5.1 Mixes it would read as normal. So this is DEFINITELY something up with HD Streams Extractor, and NOT something up with the original mix.

 

[The Scribbling Man]

I wonder if I was having a similar bit of trouble with my Lord of the Zep edit. I assumed it was a poor mix at the time... the 5.1 I extracted sounded quite brittle during loud moments, and sometimes sound fx would break up badly with little to no processing, almost like they'd been compressed several times over. It's definitely not something I usually have a problem with though. (I also use HD streams extractor)

 

[TM2YC]

I've had no problems with 5.1 mixes IIRC, just this 7.1 blu-ray. I think I found the solution. In HD streams extractor I extracted the DTS Master Audio as an AC3 with the option '-core' ("extract the DTS core of a DTS-HD track or the AC3 core of a TrueHD track"). Then extracted 6 wavs from that and it doesn't appear to be clipped, it looks like a regular 5.1 mix. There doesn't seem to be a way to do core+5.1+wavs in one setting.

 

[Silver Screen Samurai]

I've had no problems with 5.1 mixes IIRC, just this 7.1 blu-ray. I think I found the solution. In HD streams extractor I extracted the DTS Master Audio as an AC3 with the option '-core' ("extract the DTS core of a DTS-HD track or the AC3 core of a TrueHD track"). Then extracted 6 wavs from that and it doesn't appear to be clipped, it looks like a regular 5.1 mix. There doesn't seem to be a way to do core+5.1+wavs in one setting.

Thanks for this; probably going to try this method, since the copy I'm using actually comes with a 7.1 Mix as it were...
Now you're starting to make me wonder if it's actually 7.1 Mixes that are the problem; correct me if I'm wrong, but isn't it rare for them to come with most Blu-Rays? You mentioned you haven't had this problem in the past, just with this particular 7.1 Mix.

Did your print come with a 5.1 Mix, or did it only have the 7.1 Mix (hence you needing to make a 5.1)?
Mine comes with both, so I might try extracting each one and report back if I find any differences between how they turn out.
I'll be sure to keep you posted!

 

[TM2YC]

Did your print come with a 5.1 Mix, or did it only have the 7.1 Mix (hence you needing to make a 5.1)?
Mine comes with both, so I might try extracting each one and report back if I find any differences between how they turn out.
I'll be sure to keep you posted!

I've got it on DVD as well which includeds a 5.1 mix. I might extract that too and compare.

 

[Silver Screen Samurai]

I've got it on DVD as well which includeds a 5.1 mix. I might extract that too and compare.

Hey, realize it's been a while; posting, because this issue has come up again.
I'm starting to revisit 5.1 mixing, since I've now successfully extracted a 5.1 DTS and split it into Mono wavs... however, I might treat this simply as a trial run; since, as previously mentioned on this thread, when muxed from the MKV via tsMuxerGUI, they are severely clipping.

tsMuxerGUI also appears to have done this to the stereo track as well, so as an experiment I ran it through Handbrake... shockingly never even comes close to clipping when extracted that route. Obviously I won't be using a lossy Handbrake file for a final cut, but I'm starting to wonder if tsMuxerGUI is just a STRAIGHT-UP BAD software for sound extraction.

You mentioned that the 7.1 Mix you were working on for your latest edit was clipping, but that you usually didn't have problems with the app you were using, HD Streams Extractor. Is there an official download link for that software (had trouble locating it)? I'm thinking I might redo the extraction process, since severely clipping 5.1 Audio sounds... generally NOT optimal.

 

[Silver Screen Samurai]

Lowering the volume just made everything quieter, the peaks were still clipped.

Also, to finally respond to this inquiry, for me I found individually lowering the volume of each of the mono WAVs to -15 Db seemed to fix the clipping in 5.1 mixes (careful with the LFE though, you'll want to make sure boom doesn't exceed -3.7 in your software if you have it on)

 

[addiesin]

That amount may be telling. -15dB is approximately how low I have to set any added 0dB audio into any individual surround channel in my project's timeline. Sounds an awful lot like tsMuxer may be normalizing your tracks before saving them as WAV, then 6 playing at once causes the clipping. Look for some audio setting or checkbox with "Normalize" and turn it off, see if that even exists. If not there maybe somewhere else in the pipeline. Playing all 6 tracks at once should max volume at 0dB like you expect.

 

[Silver Screen Samurai]

That amount may be telling. -15dB is approximately how low I have to set any added 0dB audio into any individual surround channel in my project's timeline. Sounds an awful lot like tsMuxer may be normalizing your tracks before saving them as WAV, then 6 playing at once causes the clipping. Look for some audio setting or checkbox with "Normalize" and turn it off, see if that even exists. If not there maybe somewhere else in the pipeline. Playing all 6 tracks at once should max volume at 0dB like you expect.

So this is likely the problem, the issue is tsMuxerGUI has probably the most limited setting functionality of any demuxing software. There doesn't appear to be any way to turn off clip normalization -- or if there is, it's buried so far outside of view that apparently nobody on the whole internet can find it -- and the official tutorials for tsMuxerGUI are equally uninformative. They are sparse, at best, and contain almost no information outside the basic set of auto options and buttons. The online help forum of tsMuxerGUI is similarly unhelpful, with most people having no idea how to fix problems with it or basically saying you need to know basic programming to make it work right. I've resorted to just manually normalizing them to -15 db in Audacity.

 

[addiesin]

So this is likely the problem, the issue is tsMuxerGUI has probably the most limited setting functionality of any demuxing software. There doesn't appear to be any way to turn off clip normalization -- or if there is, it's buried so far outside of view that apparently nobody on the whole internet can find it -- and the official tutorials for tsMuxerGUI are equally uninformative. They are sparse, at best, and contain almost no information outside the basic set of auto options and buttons. The online help forum of tsMuxerGUI is similarly unhelpful, with most people having no idea how to fix problems with it or basically saying you need to know basic programming to make it work right. I've resorted to just manually normalizing them to -15 db in Audacity.

I'll check which version of it I have, because I haven't run into this issue myself. What do you use to rip? MakeMKV?

Luckily it's not the worst problem to have, the clipping isn't baked into each individual track, if it was you couldn't just lower the volume to fix it. But still it'd be nice for you to not need workarounds.