Subject:How to compare sound files?

Posted by: benjisworld

Date:3/20/2009 2:55:21 AM

I'm trying to use a common technique for data...pretty simple, just remove the vocal from one stereo track, compare it with the original, and save the difference.

I want to save the vocals but wax the instruments by removing the vocals and then comparing to save the removed part.

This will also help with bass removal so I can more easily replace kicks and basslines for remixes.

Is there a way to compare files and save the difference?

Subject:RE: How to compare sound files?

Reply by: Chienworks

Date:3/20/2009 3:41:02 AM

You can invert a file and then mix it with another. That should take care of that step. The sticky part is removing the vocal. "just remove the vocal from one stereo track" ... if i interpret that literally it sounds like you're removing the vocal from just one channel but leaving it in the other. There is no known technique for doing this.

I'm thinking you probably mean "file" instead of "track", and that you're going to use the usual technique of inverting one of the channels and then mixing them together to get a mono track. That sometimes sort of accomplishes a little bit of something. Now, the problem is, when you compare it with the original not only are the vocals different but the background is too. Let's say you invert the right channel. You now have a file that is +L-R. Invert that and mix it with the original and you'll have a file that is 0L+2R. Rather than removing the background, you've merely retained all of the right channel at twice the volume.

Supposedly the Vocal Eraser available with Sound Forge Audio Studio has some features to accomplish this. I'd guess it's only marginally successful, and only some of the time.

Subject:RE: How to compare sound files?

Reply by: benjisworld

Date:3/20/2009 3:54:45 AM

By track I mean audio file. I would say channel if I meant a specific channel.

So to be clear, I can remove some of the frequencies and then invert the file to get the data that was removed?

I just want to open a file, remove the vocals, and compare the file to save the removed data...so I am saving the data with the vocal.

Thanks for the super fast reply! I'm trying to remix a track that has a nasty bass line and boring percussion but cool vocals!

I'll be home soon to see what I can figure out. I guess I missed the "invert" function as I specifically looked for it under edit. I'll search the index to find where it is hiding.

Subject:RE: How to compare sound files?

Reply by: Chienworks

Date:3/20/2009 2:06:21 PM

Well ... a few more things to chew on.

Invert is under Process. You can select one channel first if you want to invert only one at a time.

What frequencies are you removing and why? I thought you were working on vocal removal. If you're removing some frequencies and then trying to compare that to the original file in order to keep only the removed frequencies, why not invert the EQ settings to keep the frequencies you want to begin with?

Note that removing frequencies and removing vocals have very little to do with each other. Removing vocals tends to be based on the fact that often vocals are panned center while everything else is spread across the stereo image. Combining one channel with the other negated will eliminate whatever was identical in both channels. However, it also plays havoc with the remaining material and what you have left is not even close to the original. After the vocals removal you cannot subtract what's left from the original to obtain just the vocals. This would only work of the other material was left untouched, and this doesn't happen.

Very few elements of a mix are restricted to their own frequency ranges. Bass instruments may cover from 40Hz up to 2000Hz. Vocals from 160Hz up to 6000Hz. Percussion can go from 5Hz to 25000Hz. It's impossible to use frequency ranges to remove one part of the mix while retaining the rest since they all overlap. And since it's impossible to remove one part without affecting others, you can't do the 'compare' afterwards to get back only what you tried to remove. You'll end up regaining the overlapped range of the other parts too.