Subject:can you extract a mixed vocal track from stereo audience tracks?

Posted by: bobbybobbertson

Date:1/9/2002 5:48:06 PM

I have a stereo recording. The left and right channels both have independant mics on them and a third mic was mixed into both channels. the independant mics were audience mics and the mixed mic was a vocal. thus i have:

channel 1: left audience mic + vocal
channel 2: right audience mic + vocal

I want to extract the vocal, so that I can do some work on it. Is there a function in any of the sound forge products to extract a common signal from two tracks?

Subject:RE: can you extract a mixed vocal track from stereo audience tracks?

Reply by: Chienworks

Date:1/10/2002 12:55:57 AM

WOW! That's a "toughie". Probably the answer is no, but in theory,
here's a procedure that mathematically should give you more of the
center vocal and less of the other two mics.

- Open the stereo recording.
- Invert the right channel
- Copy the right channel
- Paste Special (Mix) the right channel onto the left channel
- Copy the left channel
- Paste this left channel only to a new file and save as mono
- DO NOT SAVE the original file; close it without saving

You now have a file which theoretically contains none of the center
mic. It should have been cancelled out by the inversion and mixing. You
may have to tweak the relative levels of the source and the paste to get
the best cancellation. (Yes, i know the center is what you want to keep
and we just tossed it. Take a deep breath and keep going ...)

- Open the original file again, save this to a new file as mono
- Open this file
- Open the file you created in the previous steps (the audience only)
- Invert this file
- Copy
- Paste Special (Mix) onto the mono version of the original file
- Save this result as a new file

You have now subtracted the "audience only" from the complete mono
mix. Theoretically what you have left is just the center mic.

However, the success of the first step depends on the left & right mics
being significantly different, and the success of the second step depends
on the left & right mics being significantly identical. Obviously you can't
have both conditions true. So your end result will still contain quite a bit
of the left & right mic signal, but hopefully a lot less than the original
recording. It's worth a shot. If it's useful, kewl! If not, well then at least
you've had fun playing with Sound Forge ;-)

Subject:RE: can you extract a mixed vocal track from stereo audience tracks?

Reply by: bobbybobbertson

Date:1/11/2002 2:09:00 PM

can you explain your math??? the way I read it, this does not work.

heres what I see you have me doing:

- Open the stereo recording.
LEFT_CHANNEL = LEFT_AUDIENCE + MAIN_VOCAL
RIGHT_CHANNEL = RIGHT_AUDIENCE + MAIN_VOCAL

- Invert the right channel
-RIGHT_CHANNEL = -RIGHT_AUDIENCE - MAIN_VOCAL


- Copy the right channel
- Paste Special (Mix) the right channel onto the left channel
LEFT_CHANNEL + -RIGHT_CHANNEL

= LEFT_AUDIENCE + MAIN_VOCAL + -RIGHT_AUDIENCE + -MAIN_VOCAL


= LEFT_AUDIENCE - RIGHT_AUDIENCE

- Copy the left channel
- Paste this left channel only to a new file and save as mono
- DO NOT SAVE the original file; close it without saving
NOTE: THE NEW FILE = LEFT_AUDIENCE - RIGHT_AUDIENCE


You now have a file which theoretically contains none of the center
mic. It should have been cancelled out by the inversion and mixing. You
may have to tweak the relative levels of the source and the paste to get
the best cancellation. (Yes, i know the center is what you want to keep
and we just tossed it. Take a deep breath and keep going ...)

- Open the original file again, save this to a new file as mono
LEFT_AUDIENCE + RIGHT AUDIENCE + 2MAIN_VOCAL
- Open this file
- Open the file you created in the previous steps (the audience only)

THE PREVIOUS FILE = LEFT_AUDIENCE - RIGHT_AUDIENCE

- Invert this file
-THE PREVIOUS FILE = -LEFT_AUDIENCE + RIGHT_AUDIENCE

- Copy
- Paste Special (Mix) onto the mono version of the original file
LEFT_AUDIENCE + RIGHT AUDIENCE + 2MAIN_VOCAL
+ -LEFT_AUDIENCE + RIGHT_AUDIENCE
===============================================
2RIGHT_AUDIENCE + 2MAIN_VOCAL

- Save this result as a new file


AS I UNDERSTAND IT THE PROBLEM IS THAT IN THE FIRST SET OF STEPS (WHILE TRYING TO ELIMINATE THE MAIN_VOCAL) YOU END UP WITH ONE OF THE CHANNELS INVERTED. THIS THEN DOUBLES WHEN INVERTED AND ADDED TO THE COMPLETE TRACK IN THE LAST SET OF STEPS.

HOPEFULLY YOU CAN SEE MY POINT. THE MATH GETS LONG AND HARD TO VISUALIZE, BUT I THINK IF YOU WRITE IT OUT YOU WILL AGREE WITH ME THAT THE MATH DOES NOT QUITE WORK OUT.

Subject:RE: can you extract a mixed vocal track from stereo audience tracks?

Reply by: Chienworks

Date:1/11/2002 3:22:09 PM

Hmmmm. It looks like you're right, except for the possibility that in
mixing you'll be doing an RMS addition rather than a straight arithmetical
one. But the result is probably going to be about the same anyway. Chalk
it up to muddled 1am thinking (actually 2am in my time zone).

But now i'm scratching my head again ... we did succeed in eliminating
the left audience. We can use the same procedure to eliminate the right.
Now what could we do with those two files? Hmmmmm. Back to the drawing
board for some more figuring.

In any case, this is really just the flipside of the "remove the center vocal"
issue that pops up in the forum every now and then, which never works
acceptably well anyway.