Converting and/or Extracting MULTITRACK .M4A files

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millerTEK
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Converting and/or Extracting MULTITRACK .M4A files

Post by millerTEK »

I must admit as someone who has experience extracting multitrack WAV, etc files into their INDIVIDUAL mono WAV files which can be used for remixing - I have found multitrack .M4A files quite challenging. Discussed with others about a certain digital only source of ATMOS files with several folks who have found and distributed extractions of the ATMOS online source to .M4A files. These folks even claimed to have USED the separate channel extractions of these .M4A files to make new mixes. Funny thing, these .M4A files report as having only SIX channels - which I find odd since ATMOS contains 8 channels...

Impressed, I contacted these folks and was given sources for converting .M4A to .WAV (not asking for more details such as channel extractions, codec selections, etc) and found that these conversions only create 1 file that plays, yet the surround channels are missing. Also I tried the various conversion configs without successful results.

So has anyone actually taken these multichannel .M4A files and been able to extract all of the channels into their own single WAV files for a total of 6 or 8 mono WAV files? I'm so wanting to do some remixing as well and share reconstructions of various unreleased takes that without these discrete channels would not be possible without the usual bleed and wobble found in older attempts.

Would anyone be able to provide their procedure or private message me the info if it is some sort of secret? Having contributed items to our forum in the past - I have some ideas I want to share, too -

Thanks for your time -

steve
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Re: Converting and/or Extracting MULTITRACK .M4A files

Post by BDJ »

You can use Audacity (free) to split M4A files into separate wav's.

The Revolver M4A's that are circulating contain only 6 channels, so they are 5.1 surround files, NOT Atmos. I haven't seen any Atmos derived files obtained from streaming services.......

NB In fact, the LFE channel is often not used at all by our friend Giles M.......... :( Instead, he mixes the bass into the centre channel :o
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Re: Converting and/or Extracting MULTITRACK .M4A files

Post by millerTEK »

ah ok - I'll try Audacity and see what I get! Thanks for the direction.
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Re: Converting and/or Extracting MULTITRACK .M4A files

Post by millerTEK »

BDJ wrote: Fri Nov 18, 2022 8:58 am You can use Audacity (free) to split M4A files into separate wav's.

The Revolver M4A's that are circulating contain only 6 channels, so they are 5.1 surround files, NOT Atmos. I haven't seen any Atmos derived files obtained from streaming services.......

NB In fact, the LFE channel is often not used at all by our friend Giles M.......... :( Instead, he mixes the bass into the centre channel :o
WOW - using Audacity and the FFMPEG plugin - when I imported an M4a file (I chose Taxman as an example) I was not impressed with the separation of channels. Did you find that the Center, and Surround left and right channels are pretty much echo of items form the standard front left and right channels? I found little DISCREET audio - items that were isolated and played in only 1 specific channel. I could barely hear the cowbell.

Is this what you found? ( attached a screenshot of each channel form Audacity?)...almost makes me feel the TOUP upmixes are still superior.
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Re: Converting and/or Extracting MULTITRACK .M4A files

Post by BDJ »

That is what I also see; it is 5.1 surround, and the LFE (subwoofer) channel is not used.

Most Surround (5.1) and Atmos (7.1) tracks are not isolations of a single instrument or vocals; not just for Beatles albums but in general. The Producer fills the room (in either 2D or 3D) with sound, much like he would do in stereo. Giles M is rather conservative in that aspect, and often just fills the surround channels with reverberated front channels. He actually plays the front channels through 2 speakers in Abbey Road studio 2, and then records the sound with 2 microphones. These become the surround channels.

But..... in some cases there are isolated sounds, like a triangle, a 'cry', or short guitar riff; in Yellow Submarine, the marching band sounds like marching around you etc.

And..... in some cases you can obtain isolations by OOPSing channels, like you would do with a stereo track. But now, you can OOPS the front channels, and also OOPS the surround channels. I haven't succeeded in OOPSing a surround channel with a frontchannel, because of the delay and the reverb that is introduced to the surround channels.
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Re: Converting and/or Extracting MULTITRACK .M4A files

Post by Lord Reith »

They're basically useless apart from HTAE. I counted twelve channels and the only song that uses all of them is TNK, and even then that is just to pan the effects around the sound field. Many of the songs have multiple empty tracks or just reverb. The bitrate is also really low, even lower than the Rockband files.

It was only in the old days of anthology that we got very discreet surround mixes. Then they got wise that people were remixing them, and changed tack to make them less useful. They succeeded.
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Re: Converting and/or Extracting MULTITRACK .M4A files

Post by skynet »

Lord Reith wrote: Sun Nov 20, 2022 10:27 pm They're basically useless apart from HTAE. I counted twelve channels and the only song that uses all of them is TNK, and even then that is just to pan the effects around the sound field. Many of the songs have multiple empty tracks or just reverb. The bitrate is also really low, even lower than the Rockband files.

It was only in the old days of anthology that we got very discreet surround mixes. Then they got wise that people were remixing them, and changed tack to make them less useful. They succeeded.
The thing with DA, dear Lord is that it is by design, unfortunately, "Spectral Dolby Atmos" is just making it worst (as is not real Atmos is just a simulation, regardless of what people said about it, is not me that i am saying it, is the technical specification), Dolby Atmos is an object-based audio format that creates a sound field using height and surround sound speakers (real speakers, not earbuds, but you already know that) It is an upgrade to the standard surround sound experience, which uses traditional audio channels. As most people here is aware, traditional surround sound mix uses six channels – front left, front right, center, surround left, surround right – and an LFE track for the subwoofer (which Giles misused A LOT in the Revolver Mix). But, rather than specifying discrete channels, a Dolby Atmos soundtrack uses up to 128 audio objects. Each Atmos soundtrack will have a 10-channel 7.1.2 bed that will play on any standard 5.1 or 7.1 system if needed, Then, for systems that support Dolby Atmos, it can place a further 118 audio objects anywhere around the sound field – overhead, to the side, front to back, back to front – whatever suits the audio mix by producer design and or the action on the screen for movies. This allows specific sound effects to move independently around the room while the channel-based audio bed carries on underneath. The thing about using audio objects is that playback isn’t tied to a single speaker layout, and an Atmos soundtrack will adapt to the speakers available in the room... so for de-mixing a DA mix (in particular spectral ones) it will become a rather difficult and daunting task than to do it for a "traditional" surround mix, lots of people here and out here have tried, with varied degrees of success to de-mix the new revolver, but it will never work out completely, and i know people can keep trying, but to get a "decent" de-mix, the source objects are needed, is the equivalent to have access to the master tape, and not that Giles has made a great DA remix for Revolver (i loved what he did for Sgt. Pepper, The Beatles, Abbey Road and LIB by the way in the DTS department, and so, so on the DA mix for AR and LIB), actually his mix is pretty basic, but he did took all the objects available (and you can see part of his work base line in the picture that he shared a couple of months back in twitter) and "remixed" (or retooling) them based on a map designed by him as a producer, so unless you have access to the actual hard drive in which he saved those objects (and the object can be anything, from the feedback guitar sound that he removed from Taxman to the voices of each Beatle), it will be always a nice but rather poor attempt at have a better "surround mix"

Yes lord you are right, they configured the objects so when you separate the channels from the final master you will get a lot of bleed sound, artifacts, and low quality signals unfortunately :( as what you need to do is not a de-mixing process, is basically software Reverse Engineering
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Re: Converting and/or Extracting MULTITRACK .M4A files

Post by BDJ »

Thank you, Skynet, for the insights in Atmos technology!

I found the picture that you mention of Giles Martin's setup on Twitter. Fascinating!

The monitor on the left shows the channels ('beds' as you call it), and on the right monitor are the volume meters and the placement of the 128 objects.

Looking at the waveforms, Giles is actually here mixing Got To Get You Into My Life.

The right monitor shows the volume (green bars) of the channels (beds). There are 12 volume meters (and an overall volume meter), indicating that there are indeed 12 channels. Looks like a 7-1.4 configuration (i.e. 4 channels in the ceiling). This matches what Lord Reith said (12 channels), but Skynet mentions 10 channels. Perhaps Atmos can be configured with different numbers of channels?

I also see on the left monitor how heavily Giles is compressing the channels; the waveforms look like bricks....that is one reason I don't like Gils' mixes very much.
Channel 4 has no volume, this is probably the LFE (subwoofer) channel. Giles mixes the bass into the front centre channel (no 3).

Also note that the bottom 2 channels are copies of the top 2 channels. Looks like Giles is bouncing the front channels to the surround channels, as we suspected!

Unfortunately, I am not familiar with the meaning of the indicators of the objects, in the right monitor; not clear if Giles is actually using objects here, or is just playing the 7.1.4 beds.

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Re: Converting and/or Extracting MULTITRACK .M4A files

Post by skynet »

BDJ wrote: Wed Nov 23, 2022 11:25 am Thank you, Skynet, for the insights in Atmos technology! ...
np. Glad it is useful information
BDJ wrote: Wed Nov 23, 2022 11:25 am
... The right monitor shows the volume (green bars) of the channels (beds). There are 12 volume meters (and an overall volume meter), indicating that there are indeed 12 channels. Looks like a 7-1.4 configuration (i.e. 4 channels in the ceiling). This matches what Lord Reith said (12 channels), but Skynet mentions 10 channels. Perhaps Atmos can be configured with different numbers of channels?
Yes indeed it can be 12 channels (10 channel "programming" is the recommended estándar), actually that can be expanded as need, as per the technical explanation from Dolby itself:

" A bed is a channel-based premix or stem that includes multichannel panning, and does not need dedicated panning via Dolby Atmos metadata. Use a bed for stereo or surround panning. A bed can be thought of as a traditional channel-based stem with the rules and expectations of stem configurations (such as 2.0, 5.1, and 7.1). These are fixed locations in space that are tightly constrained to traditional speaker environments, including theatrical environments where a speaker array might be used.

In Dolby Atmos, the largest bed configuration that exists is 7.1.2. This configuration allows for Low-Frequency Effects (LFE), with left and right side walls, and an additional overhead stereo pair. Dolby Atmos supports the use of multiple beds." (https://professionalsupport.dolby.com/s ... uage=en_US)

For example you can use up to 118 objects. However, the first 10 objects are reserved for the 9.1 Dolby Atmos bed and are excluded from mapping. Therefore, it is recommended that the 9.1 Dolby Atmos bus uses the first 10 device ports of your audio interface, since a bed is used to send sources to specific channels within the array. For example, if you had a stereo recording of a piano, you might then decide to send those two sources to just the L and R channels. Within the mix, you can have beds that output in any number of configurations including standards like 5.1 and 7.1. It’s also useful from a processing perspective as you can treat the bed as a single part. Think of it as Atmos equivalent of a channel. An object can be moved around freely inside the room 3D space, including automation of position, height and size, or "intelligent placement"
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Re: Converting and/or Extracting MULTITRACK .M4A files

Post by BDJ »

Thanks. As I understand Atmos, the maximum number of 'beds/channes' is 32. This allows for 'home' configurations like 7.1.4 or even 9.1.6.
In theatres and cinemas there may be even larger number channels (up to 32).

https://professionalsupport.dolby.com/s ... uage=en_US
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