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One example of attempting ulf recovery


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Bought movies yesterday without consulting data-bass, big mistake of course.

So, is it possible to fix the misery, or is there no hope.


The movie Battleship seems to have a fairly steep filter applied at around 35Hz, there is virtually no low bass left.

It is reasonable to assume that the sound effects had a much wider frequency distribution originally, and that some of this can be recovered as long as it is not buried in the noise floor.


Original lfe:




Some work with eq and filtering, and this is the result on the lfe track:




So, how does it sound.

Well, it has improved, the balance of the bass range has improved a lot, there is more weight and impact, but I still believe the better productions sound far better, eq can only do this much.

I have not watched the whole movie yet, only a couple of scenes to verify the lfe eq fix.


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Careful you don't clip the waveforms...make sure you can check to see if you do.


Often a highpass or shelf  filter is used in production to preserve headroom......headroom that would have been taken up by the very freqs you are attempting to 'bring back'.



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I do read that a lot, but the extended Hobbit film that had the extra bass in the extended bits (compared to the anaemic theatrical release) seemed to have exactly the same top end despite the extra bass, so clearly people are applying filters in some sort of paranoid state! :wacko:  :rolleyes:  Annoying!

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Very hard to know without knowing who mixed and created the sound for a film....if the director was present for theatrical mixing and said 'louder', a shelf filter would allow that to happen quite easily, as film sound stages rarely can monitor below 25Hz, and taking away <20Hz info would give you more headroom for the louder >25Hz info (due to Equal Loudness Curves)


On the other hand, when the Tron:Legacy BD was made in 7.1, the director personally made some changes to the soundtrack, which could have led to the infamous clipping/hard limiting present on every channel in that track except the LFE channel.... again conjecture.


For Avengers, it was reported that the mixing stage suffered some downtime due to blown subwoofers. Mixing time is not cheap, and it is my guess that those blown subs caused the very steep shelf to be applied to Avengers. Again, just a guess, but one that appears to fit the facts, as I currently misunderstand them.


I would love to know where The Incredible Hulk was mixed, and whether or not the folks that mixed it knew what was going in. I have studied that film carefully, and not only does it contain powerful ULF, but I cannot find obvious clipping anywhere on that track. The sound team used their headroom wisely and applied ULF where they had headroom to do so, and also used mid bass slam to great effect (the individual gunfire at the university, and esp. When the sonic cannons turn on). Decent film, too.



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Careful you don't clip the waveforms...make sure you can check to see if you do.


Often a highpass or shelf  filter is used in production to preserve headroom......headroom that would have been taken up by the very freqs you are attempting to 'bring back'.




Clipping is no problem, just watch and learn from the professionals.. or maybe not.


Here is what I did to fix this one, if I remember all stages correct:

- 8192-tap eq with reduction around 40-60hz and boost below 30hz -> some headroom gained, less 50hz-boom.

- 12hz hp filter 24dB/oct,

- Boost around 16hz, +22dB, here is where you definitely want to check the levels.


Planinng to watch this movie now tonight, with the "ULF Remaster2" sound track.


Some of the same effect can of course be done by applying eq to the playback system, such as in the dsp for the subwoofers, but no sane person will allow a 22dB 14hz boost, and you would certainly need to check the whole movie first.

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This is an interesting prospect, kinda like what I've seen attempted in the JRiver and Audacity forums, but I think it's a very tough thing to get right.  None of those attempts sounded like they improved things overall, but I hope you'll keep us posted!  :)

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I agree, nube, I have tried eq on different sound tracks, and my experience is that it is very difficult to get an overall improvement, for a number of reasons.


This one, however, seems to have improved.

I managed to keep the upper-bass slam, and bring back some of the low frequency balance.

I would say the eq-fix improved the overall experience on this movie.


However, I did not find the sound track very good.

It is mixed very loud, causing it to sound rather flat and tiring.

Half-way into the movie I just turned it down to -20dB, now having heard all the sound effects that sounds more or less the same, and the floor still gets a subtle shake.

There is no way to bring back lost dynamics.


I got the impression it was mixed by a kid using a cell-phone for monitoring and editing on a free downloaded app.

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There is no way to bring back lost dynamics.


I got the impression it was mixed by a kid using a cell-phone for monitoring and editing on a free downloaded app.


Are you still talking about the Battleship film?


What tools are you using to implement the EQ to the track?



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Yes, Battleship is the movie.


When I say it does not sound very good overall, that does not mean it is among the worst ones, far from that.

And my opinion is that the re-eq improved overall quality on this one (Battleship).


I used Audacity, it has all that is needed to do a job like this, note: for amateur use only!

Any pro video editing suite should be able to do this as well, but you would not buy such software unless you intend to use it professionally.


To work on the DTS-HD track you need to extract it first.

When completed, you mux in the edited sound tracks in to the original file.


This experiment was just for fun, to see if it is possible to improve something. 


I worked in a company around 1995-1996, where I got involved in selling and servicing the first generation digital on-line editing software.

The computers could just barely manage broadcast quality, and very expensive hard drives were needed, and then they could hold perhaps an hour of program material in total.

Today is a completely different world.


If the re-eq can work or not, depends on the program material, if one of the last steps they did was to filter the lfe, then there is some hope.

But what content actually is present in the ulf is pure luck, as they most likely did not have any way to monitor this in the studio.

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Audacity is a powerful program for being freeware.  


Look forward to seeing what you come up with.


The greatness of 24-bit audio is that if it was filtered down with a shelf, it can likely be brought back with an opposite shelf.  Battleship appears to have a very strong shelf applied to it prior to your EQ.



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Yes, with 24-bit the noise floor is so low that it will actually be possible to bring back things that were removed.

But even with 16-bit resolution there is enough dynamic range to be able to bring back ulf from a filtered lfe track.


Still, there must be content that makes sense to restore, other movies I have attempted the same approach on have not been so succesful.

You can bring back the spectral balance, but if the ulf is mostly noise-like and does not bring any more impact and definition to the whole experience, then it may not improve things at all.


This was a one-off, no plans for doing the same process on other films.


I have a step-by-step write-up of the practical parts of the process on the htpc, if someone is interested.

Gets you to the point where you start applying eq in Audacity, though good computer skills are required. 


The eq is the difficult part, and where you really need skills and experience in sound and listening and signal processing to be able to improve things.

This will also be different for different movies, and thus can not be easily automated or described in a simple, predefined procedure.


Generally, one should start by reducing the level to gain headroom, you need to make room for the bass you bring back.

Often these sound tracks have a boom-bass boost around 50hz, which can be eq-ed down a bit, and this alone can actually improve the sound, and it will gain some headroom.

Removing too much may lead to loosing whatever good there was in the original sound.

Then, apply a high-pass filter to remove content below where you think it is unlikely to find useful content, to avoid too much ulf noise when you bring up the low freqs.

Last, apply a huge eq/bass-boost to bring back the ulf, you use frequency spectrum analysis to determine how.


As I see it, this is fun just to try it, but I do not believe this is a useful method of fixing movies before you watch them, even though it worked on Battleship.

First, you would need to check the movie - before you watch it - to verify if the low bass is filtered.

Then you would have to go through the rather elaborate task of attempting to fix it, it will take some time, handling 30gig files takes time.

And when you have the new sound track in place, you compare against the original, and may have to conclude that the original sounds better overall, despite the effort.


Low bass is important to get the best experience, a filtered sound track sounds like something is missing, it is not only about shaking the house more. 

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Here is the complete sound track remaster guide, note that I wrote this primarily for myself, so that I could replicate the different steps later when I have forgotten what I did and what applications I used:


Legal notice, just for the record, to show that we are not doing anything that compromises copyright, because we are actually the good guys:

This is a description for how to remaster sound tracks in existing video files in digital files, such as the .mkv format.

Any practitioner of this process must take appropriate action to ensure that copyright laws are not compromised in any way.

The practitioner must ensure that changing the original copyrighted material does not compromise copyright laws, even if the changed copyrighted material is intended for use solely by said practitioner.

It is not legal to distribute copyrighted material, be it part of originally copyrighted material or the complete copyrighted material, and It is not legal to distribute copyrighted material that has been altered in any way, be it part of originally copyrighted material or the complete copyrighted material

(The short version: You can not distribute or share remastered sound tracks, even if you leave out the movie, and it may be problematic to make changes to copyrighted material, even if you are the only one using it. But it is of course allowed to use any eq or signal processing when playing the material, which is what we are doing here, if anyone asks.)





How to re-master audio by changing original audio track using audio processing such as filters and eq on a HD .mkv video file:


First, copy the movie to a set of manageable sized files for further processing.
Now, for each of these files, extract the audio, re-master process it, and put it back.
The re-mastered movie files can then be merged back in to one large .mkv.

Update 16092013:

Audacity can import file formats supported by ffmpeg.
Movie file (.mp4, .mkv) can be opened in Audacity directly, and audio channels is imported automatically.

Update 27082014:

Even large .mkv files 20-40GB can be processed directly by importing it in Audacity, or by extracting the audio tracks first and then open the extracted audio in Audacity.
The import process will take a long time.


MKVToolnix, with mkvmerge GUI and MKV Extractor GUI.
Spectrum Lab spectrum analyzer (windows only, but runs fine in Linux on WINE).
Audacity for audio analysis and processing.
tsMuxerGUI for .m2ts extraction.

1. Copy movie to a set of manageable sized files:

Use mkvmerge GUI to create a copy of the original movie spread out as many smaller separate files.
Approx 2G size is fine, this gives approx 20 files for a 40G blu-ray mkv.

Example files:
movie.mkv: original movie file, often horribly large.
movie-001.mkv .. movie-0xx.mkv: Set of new. smaller movie files created now.  

2. Extract audio:

Use MKV Extractor GUI to extract the audio tracks, select the desired one.
DTS-HD MA will end up as a file with .dts ending.
For lossless DTS use something to convert the DTS-HD MA to LPCM, then extract the LPCM using MKV Extractor GUI.
DTS-HD MA lossless will end up as a file with .pcm ending.
MKV Extractor GUI will extract to files named 1_Audio_dts_eng.dts or 1_Audio_pcm_eng.pcm.
Rename those files immediately after extraction to the same name as the movie file, keeping the .dts or .pcm extension.   

Example files:
movie-001.mkv: Smaller movie file.
1_Audio_xxx_eng.xxx: MKV Extractor GUI extracted audio.
movie-001.dts: Extracted audio tracks from dts (MA+core).
movie-001.pcm: Extracted audio tracks DTS-HD (Lossless 24bit, 7.1).

3. Re-master:

Open the audio tracks, .dts or .pcm, in Audacity, and get a set of PCM channels, where ch1=L, 2=R, 3=C, 4=LFE, 5=RL, 6=RR, 7=SL, 8=SR.
Actual number of channels depends on the source, many are only 5.1 and thus will be 6 channels in total.
If using the .dts file, the 24-bit channels are decoded to 16-bit, max 5.1 channels, because Audacity does not decode MA, only core.
Use the .pcm file to get full HD with all 8 channels.

Audacity has a built-in spectrum analyser.
For external analysis in Spectrum Lab, export individual tracks in wav-format.

Now play with the file and apply any desired filtering or eq or other audio effects.

When done, export all tracks to a PCM file (Export, then select Other uncompressed format).

Update 27082014:
Audio can be exported as .flac and be muxed back in to the video file in .flac format.

This must of course be done for all individual movie file parts, if the re-master processing is to be applied to the whole movie.

Example files:
movie-001.dts: Extracted audio tracks.
movie-001.pcm: Extracted audio tracks.
movie-001 SL.wav: Single track exported for Spectrum Lab analysis.
movie-001 Remaster.wav: Re-mastered audio tracks.

4. Add re-mastered audio track:

Use mkvmerge GUI to add the re-mastered audio tracks to the movie files.
This must of course be done for all individual movie file part, if the re-master processing is to be applied to the whole movie.

Example files:
movie-001.mkv: Smaller movie file.
movie-001 Remaster.wav: Re-mastered audio tracks.
movie-001 (1).mkv: Smaller movie file, now with additional re-mastered audio track.

5. Merge all smaller files back to one movie:

Use mvkmerge GUI to merge all the new re-mastered files in to one large movie.

Example files:
movie-001 (1).mkv .. movie-0xx (1).mkv: Smaller movie file with re-mastered audio.
movie Remaster.mkv: Finished movie with re-mastered audio.

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Regarding how to implement this equalization;


Using a dsp, be it a standalone unit or software plug-in in a computer, is likely to be the best alternative to implement this.

If you use a computer player, with a media center like JRiver, it is possible to do the equalization properly, and the film can be played from different sources, such as streaming from the net, or bluray.

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