Reverse AnalogX Vocal Remover?

[EmpireStrikesBack198]

Hi,

I was wondering if there was a program like AnalogX Vocal Remover except that it leaves behind the center part eliminating the left and right sides. I have a track where I only want the center part. I have tried Audacity and Adobe Audition's built-in remover and played with that, but it was unsatisfactory. If you would like me to attach a clip of what I'm working on, I will gladly do that. Thank you!

Blake

[Gavino]

Centre removal works by subtracting one channel from the other (or adding one channel to an inverted form of the other), thus eliminating the common part. More generally, any signal that is present in both channels in some proportion can in principle be removed by subtracting the two channels in the inverse proportion.

However, what you want to do is remove everything except the sounds placed in the centre.
That's not going to be possible unless your recording contains only a limited number of discrete sources outside the centre, eg one instrument panned (more or less) left and one (more or less) right. Most recordings have a range of sounds, each panned at different positions.

[jagabo]

Look for a Dolby Prologic surround sound decoder filter.

ffdshow includes one. You can build a filter graph to use it:

https://forum.videohelp.com/threads/323192-Demux-a-Dolby-Surround-2-0-file-into-separat...=1#post2002645

That's about the best you can do, I think.

[EmpireStrikesBack198]

Centre removal works by subtracting one channel from the other (or adding one channel to an inverted form of the other), thus eliminating the common part. More generally, any signal that is present in both channels in some proportion can in principle be removed by subtracting the two channels in the inverse proportion.

However, what you want to do is remove everything except the sounds placed in the centre.
That's not going to be possible unless your recording contains only a limited number of discrete sources outside the centre, eg one instrument panned (more or less) left and one (more or less) right. Most recordings have a range of sounds, each panned at different positions.

I think I may need to attach some samples so you can better understand what I am trying to achieve.

This is original clip without AnalogX applied: http://www.sendspace.com/file/fzhf9c

Here is the same clip with AnalogX applied: http://www.sendspace.com/file/g5a3rv

The music in this track is completely in the center while the sound effects aren't. My goal is to keep only the music, though. AnalogX removes the music, keeps the sound effects and converts the sound effects to mono. It seems like there should be a way to "reverse" the process and eliminate the sound effects (left and right) leaving behind the music (center).

Look for a Dolby Prologic surround sound decoder filter.

ffdshow includes one. You can build a filter graph to use it:

https://forum.videohelp.com/threads/323192-Demux-a-Dolby-Surround-2-0-file-into-separat...=1#post2002645

That's about the best you can do, I think.

I will try out what that link suggests and see if that works for me. Thanks.

[jagabo]

Look for a Dolby Prologic surround sound decoder filter.

ffdshow includes one. You can build a filter graph to use it:

https://forum.videohelp.com/threads/323192-Demux-a-Dolby-Surround-2-0-file-into-separat...=1#post2002645

That's about the best you can do, I think.

I will try out what that link suggests and see if that works for me. Thanks.

Prologic separation of the center channel doesn't work as well as vocal removal. I'd say it may remove about 50 percent of the howling.

[netmask56]

The problem is one of basic algebra - the way a stereo recording is made with an apparent centre channel. The centre channel is actual a mono signal mixed into the Left and Right channels with equal level.

So

Lt = L + 1/2C
Rt = R + 1/2C

If you combine the 2 signals in phase or adding then you get a classic mono signal = L + R + C
If you combine them with one channel reversed in phase so they subtract you get L-R
More fully (L+1/2C) - (R+1/2C) so the C component cancels out leaving a mono signal equal to the left and right components.

Fiddle with the figures as much as you like and you can't get an isolated C signal

Think of each channel as a standalone mono recording consisting of an orchestra and vocalist mixed together - you can't isolate either in a mono recording - yes you can fiddle with frequency band splitting bu that doesn't give you 2 discrete signals

Lt = Left total
Rt = Right total
1/2C = half centre

I believe there is a substantial prize from one of the mathematics department of a University for the first person to come up with a mathematical solution to extract C in total isolation.

[Gavino]

I believe there is a substantial prize from one of the mathematics department of a University for the first person to come up with a mathematical solution to extract C in total isolation.

LOL
Yes, basically you have 3 unknowns, but only 2 equations, so insoluble.
You can eliminate any one of L, R, or C, but not both L and R (or any pair).

As I suggested above, a signal at any given pan position can be eliminated.
Say you had signals L and R panned 90% left and right respectively.
Lt = 0.9L + C/2 + 0.1R
Rt = 0.1L + C/2 + 0.9R
then you could eliminate L by doing
(9Rt-Lt)/8 = R + C/2
But you can't then repeat the process to eliminate R and extract C as you only have one signal (or equation) containing R and C alone. So what I said earlier:

That's not going to be possible unless your recording contains only a limited number of discrete sources outside the centre

is wrong, and the techique only works if there is just one other sound panned off-centre.

[jagabo]

I think the Prologic filter creates a center channel by essentially multiplying the two channels together. So anything that's common to both channels is louder than anything that's not common. But you still have residual sounds from the left and right channels in the center channel mix.

[EmpireStrikesBack198]

What if you remove the center channel leaving behind the left and right channels and take that L and R, invert them, and mix them back into the original track? I think you can do something similar with the center channel extractor in Audition. However, AnalogX converts the processed track to mono, which means you would have to convert the original track to mono to eliminate the, what were, the L and R channels. Then again, won't inverting only work with stereo tracks?

[Gavino]

What if you remove the center channel leaving behind the left and right channels and take that L and R, invert them, and mix them back into the original track?

As netmask56 explained symbolically, when you remove the center channel, you don't get the left and right channels individually, you get a single track of L-R. There's no way of mixing that back with the original track to eliminate both L and R.

Then again, won't inverting only work with stereo tracks?

It works with both stereo and mono.
(Inverting doesn't mean switching right and left, it means changing a positive level into a negative one and vice versa.)

[jagabo]

It's fundamental math. You have three unknowns and only two equations. There is no way to solve the problem.

[netmask56]

Re Gavino - you could of course simply turn off the Left channel then you would have R+C no need to pan
And of course if you tried a vocal remover on one of my commercial releases you would run into the problem that I nearly always put the vocalist through a phase shuffle circuit ( a modified Sansui QS1 professional encoder) that wobbled the phase through 45° to 90° and spread the reverb so vocal cancelling was never 100% possible. This technique gave the vocal a forward presence.

[Gavino]

Re Gavino - you could of course simply turn off the Left channel then you would have R+C no need to pan

That's obviously true for your original example.
My example was a different one (with the panning already in the source), intended to show how the centre removal technique can (in principle, at least) be generalised to remove signals from any panning position.

[EmpireStrikesBack198]

Thanks for helping me understand clearly why what I suggested isn't possible. I figured that if you could remove the center channel, then you could do the reverse. I guess you really can't unbake a cake. Boy, do I hate the feeling of defeat.