Question about Normalization (how does it work in Audacity?)

[Ral-Clan]

Very glad I could shed some light onto and contribute to the development of one of the 'net's best open-source projects.

[steve]

Changing the stereo image is show damage, and better, it's damage that you can't readily recover from without UNDO.

You can "recover" from it just by adjusting the "pan" position.

I must admit, I am not entirely clear on what "DC offset" is.

DC_offset.png (8.62 KiB) Viewed 2934 times

Am I correct in my deduction that Audacity's Normalize function treats the left and right channel separately? If so, why would anyone practically WANT to do this. It would destroy the left and right balance of a song, for instance.

Today I was recording a band - just an ambient recording with two microphones connected to a Digidesign system with ProTools. I had a matched pair of microphones, but my gain levels were obviously a little off and the right channel was a little quieter than the left channel.
I needed to normalise the track as I'd left plenty of headroom (live band) and was wanting to burn it to CD.
After Normalizing, I found that the left (louder) channel was nicely normalised, but the right (quieter) channel was still noticeably quieter.
Solution - export from ProTools, import into Audacity, Normalize, burn to CD.

I thought of another problem. Say one channel's sound is just above noise for the whole performance. Normalize would turn that show into garbage.

Garbage in, garbage out. If one channel is just above the noise floor, it begs the question "Why?" There's not much that you will be able to do with that channel anyway, apart from silence it.
If it is not quite that low, but low enough that normalizing will bring up the noise floor too high, panning the stereo to bring that channel back down to the correct level relative to the other track will also bring down the noise floor. I can't think of any real life situation that this would happen - If the L/R ballance is that far off, why not just record it in mono and pan it to the left or right? (the result will be a cleaner recording).

[steve]

<<<I think it might be useful if there was a tick box in the Normalize function that offered something like "tie stereo pairs" or "preserve stereo balance" as an option. That way one could import a number of stereo songs and normalize them all to the same level, but keep the relationship between each song's left and right track intact.>>>

That's how I thought it already worked. Imagine my surprise. I believe it should normalize a stereo pair tied and independently if they're split. Normalize should introduce no damage and only change levels. Changing the stereo image is show damage, and better, it's damage that you can't readily recover from without UNDO.

I thought of another problem. Say one channel's sound is just above noise for the whole performance. Normalize would turn that show into garbage.

I wonder how my other editors work...

Koz

This is a bit of a late post, but if anyone is interested here is a "Normalise" plug-in that works with stereo pairs.
Any feed-back / comments most welcome.

(new version now available - see later post)

[kozikowski]

Cool Edit 2000 provides a link/unlink check box. I believe the default is to link.

Koz

[steve]

It would be easy enough to put in an option, but the Normalize effect in Audacity already does that so I didn't think there was much point.
....
.... Just seen your PM. Glad you like it
Will add an "unlink channels" option and post it here.
What would you like that feature called? "Split channels"?

Any other improvements that you can think of?

[kozikowski]

CE2K has a check box called [Normalize L/R Equally]. It comes from the factory checked.

Koz

[steve]

New version give options for equal L/R processing (linked channels) or independent L/R processing (split channels).
Quite a few other minor changes, mostly under the hood, but you will notice some change in the GUI.

Don't some of the Audacity tools have the "-" built in? I'm perfectly happy with it the way it is, but it may not be consistent.

I never did like that "-" in the built in Normalize effect. IMHO if you want to normalise to 6dB then you should enter 6dB and that should mean +6dB. It seems silly to have to enter "-6" to set it to "+6". Also, with the limited flexibility in the Nyquist effect interface I could not have a "pre-printed" minus sign even if I wanted one.

The file name of this version has changed (so that I did not get mixed up with the previous version), so you will need to manually delete the old version from your plug-ins folder. As before it will be listed in your Effects menu as "ESP Normalise" (to distinguish it from the built-in Normalize effect).

There are a couple of limitations of this plug-in;

As with all Nyquist effects, it can be rather slow processing long tracks and if the computer has insufficient memory attempting to process too much audio could cause a crash. It should not be particularly memory hungry, but probably not a good idea to try it on hugely long tracks.

If the track has such extreme DC offset that the waveform is entirely above, or entirely below the horizontal 0.0 line, then the "Absolute" DC offset correction will be unable to correct it in one pass. I don't imagine that this will occur very often.

[Irish]

I have been using Audacity for a number of years now, mainly digitising LPs, and I have learned a lot from the forum. However, this is the first time I have been moved to contribute.

A big thanks to stevethefiddle for pointing out the workings of the Normalise function and for his revised version.
It looks as though I'll have to look again at some of my recordings!

PO'L

[kozikowski]

<<<Garbage in, garbage out. If one channel is just above the noise floor, it begs the question "Why?">>>

Because that's the way the producer wanted it. I'm extraordinarily popular at work because I never cross the Producer/Engineering boundary.


<<< kozikowski wrote:Changing the stereo image is show damage, and better, it's damage that you can't readily recover from without UNDO.>>>

<<<You can "recover" from it just by adjusting the "pan" position.>>>

I agree completely. Where was it originally, and how do you keep from affecting the louder of the two channels?

Koz

[steve]

Because that's the way the producer wanted it.

Then it begs the same question of the producer, which for people on this forum is likely to be the same person as the engineer (and probably also the director, performer ...)
I think we were talking about normalising/amplifying the complete show, in which case it seems more likely that the stereo mix would be way out of balance because of the engineer messing up rather than because the producer wanted it that way.

Of course you do have a very valid point in that sometimes the left and right channels DO need to have different peak levels. I had a good example of this recently with a violin / piano duet. The piano was to the left, and the violin to the right. Because of the piano waveform had a more "peaky" shape than the violin and there was more piano on the left than on the right, the Normalize effect would have amplified the right channel too much, thus making the violin too loud compared to the piano. In cases like this the ability to link channels on the Normalize effect is what is needed (or use the Amplify effect).

I agree completely. Where was it originally,

I'm a believer of "if it sounds right, it is right".

and how do you keep from affecting the louder of the two channels?

It doesn't. The pan slider is not a true "equal power" pan, it just lowers the level of the channel that you pan away from.
If you pan 70% to the right, it does not do anything to the Right channel, it just lowers the level of the Left channel. This is possibly not as good for mixing large multi-track recordings, but it is a lot easier for most users as it avoids inadvertently clipping as a result of panning a normalised stereo track.