Audacity Forum

Robert J. H. wrote:Pretty complicated the whole Fourier stuff.

I'm impressed
I was wondering why we had not heard much from you for a while. I'm looking forward to seeing your code.

steve wrote:

Robert J. H. wrote:Pretty complicated the whole Fourier stuff.

I'm impressed
I was wondering why we had not heard much from you for a while. I'm looking forward to seeing your code.

The subject is quite absorbing. Hundreds of pages to read in order to aquire another little bit of useless knowledge - in the sense that it doesn't have a bearing for the subject at hand.
The stupid thing is that all important formulas are in a graphical format - which seldom can be read correctly by a screen reader. It is all "dead reckoning" in the end.
The code is at the current stage quite a mess - or to put it more elegantly - it has still some redundances.
The audio example above had indeed a overlap of 4096 samples (without zero padding) and a simple triangular window.
There was in fact a little bug. the last sample was a 1/4096 too low. However, I doubt that this is responsible for the slight click.
I am sure that a lot of other bugs will loom up once the first plug-in version is submitted.
So, butter your sandwiches and heat up your tea/coffee water...

Ok, that's the first attempt:
Center Removal, Isolation and more
The tool is - as it is - not specialized for center isolation (including echo cancelling and such stuff), but it attenuates at least by 3 dB (near the center).
This value increases rapidly towards the sides.
You can control which portion of the stereo field should be attenuated the most y choosing "Isolate Center (inverted)" and applying it on a duplicated track.
If you change the gain of the original or the copy, the focus that cancels some part moves gradually sidewards.
Happy experimenting.

The trick to better de-mixing of Beatles tracks is that you FIRST have to fix the azimuth.

On almost all the Beatles song (remastered ones for sure) the left and right channels are not perfectly in sync. One channel is always 1 digital sample offset from the other channel, sometimes 2. Money is 6 samples offset.

You have to strip the stereo into separate left and right channels and then move one channel ahead or behind the other. In my program I play the tracks with the stereo width set to 200% (which is same as OOPsing) and when the channels are in sync the vocal will disappear. When you re-sync the channel it'll eliminate the vocal sibilance artifacts. Then down-mix that to a new stereo mix and you're resulting isolations will be far better.

lancehall wrote:The trick to better de-mixing of Beatles tracks is that you FIRST have to fix the azimuth.

On almost all the Beatles song (remastered ones for sure) the left and right channels are not perfectly in sync. One channel is always 1 digital sample offset from the other channel, sometimes 2. Money is 6 samples offset.

You have to strip the stereo into separate left and right channels and then move one channel ahead or behind the other.

That's a rather old thread that you've posted in.
The post before yours has the link to the plug-in that does stereo vocal removal/isolation. It also has the option to shift a channel an arbitrary number of samples.
Some people find this feature intimidating.

In my program I play the tracks with the stereo width set to 200% (which is same as OOPsing) and when the channels are in sync the vocal will disappear. When you re-sync the channel it'll eliminate the vocal sibilance artifacts. Then down-mix that to a new stereo mix and you're resulting isolations will be far better.

Could you explain that in more detail? (in the plug-in thread itself would be best)
Stereo widening of 200 % implies normally that one channel has a inverted polarity. It could also be seen as having mid in one channel and side in the other channel.
The plug-in has also a analyse feature that shows the correlation between the two channels.
I could add:
- absolute stereo width (max or average)
- temporal alignment (within 10 samples for instance)

I always appreciate new input.

I'm just saying the one sample mis-alignment is something most people don't know and it's why isolations are not as good as they could be. Actually it's probably slightly more or less than an exact sample.

I've been de-mixing and remixing the Beatles for 15 years and it's when I figured that out is when I started getting good isolations. Also learning the actual EMI EQ points greatly improved my mixes.

I flip on the live OOPsing (stereo width) just so I can instantly monitor the manual re-alignment I am doing. It has nothing to do with the rest. I'd rather do it manually because I know it'll be right.

I use the Center Channel plugin.

The other manual step is using an inversion of the center extraction to subtract from the Left and Right channels instead of doing another plugin pass with the stereo sides only setting. That guarantees that the Left and Right isolations are perfect fits with the center channel information and less artifacts.