Reverse volume normalization?

[jhenderson01075]

Hi -

Unfortunately, I have ripped a substantial number of my CDs to FLAC format with volume normalization enabled. For classical music, this causes the noise floor to change noticably between tracks, which I find noisome.

So, I'd like to reverse the normalization. But, I haven't found a utility to accomplish this. If I proceed and write one, shouldn't it be possible to open the FLAC, parse the audio information into a buffer and calculate the minimum amplitude value within the buffer and use that as a scalar value to be subtracted from each sample within the buffer to effectively denormalize back to zero?

Thanks,
Jim

[ChristinaS]

Re: Reverse volume normalization?

Volume normalization involves some passages having been raised in volume, by varying degrees, while some not at all. I doubt you can reverse the process.

[jhenderson01075]

Why not?

Thank you very much for your response. But, here's why I would have thought it could work:

During the normalization process, the track is scanned in its entirety to determine the maximum amplitude present - call this Tmax. The maximum amplitude that a 16-bit Redbook track can contain is 2^16 or 65535 - call this RBmax. One only needs to add the scalar value of (RBmax-TMax) to each sample in the track to effect the normalization.

To undo this process, why couldn't I scan the track to determine the minimum amplitude present - call this Tmin. I should only need to subtract the scalar value of (Tmin) from each sample in the track to effect the denormalization.

What's wrong with this approach?

[ChristinaS]

Re: Reverse volume normalization?

I think you might be referring perhaps to volume boost which is a constant amount added, and it can be reversed by volume quieten - but beware of clipping which may have already occurred through the boost, that would be distorsion which cannot be reversed - it would simply be a quieter distorsion.

Normalization boosts the volume in varying amounts all along so you can't tell how much if anything was added at any one point. It is my understanding that it is an irreversible process.

If I'm wrong, Spoon or other specialists will be along soon to set me right :D

However not to mistake volume normalization performed on an audio file during ripping or conversion process and volume normalization applied to an audio file as it is being played by a player such as dAP. In the first case it is a permanent modification of the wave pattern, in the second case it is an indicator only for purposes of playing it, so it can be removed, as the file itself is not being changed.

[jhenderson01075]

To clarify...

I am referring to the volume normalization that is part of the PowerPack in dBPowerAmps Music Converter application.

Unwittingly, I enabled that option at some point when ripping my CD collection. I suspect that it occured when I upgraded to v11.

Jim

[jhenderson01075]

How is volume normalization implemented?

Is normalization is implemented as a scalar multiply instead of an add? If so, why is this done when a simple addition of the delta value I discussed initially would have sufficed?

If normalization were implemented as an addition, the process would introduce no signal degradation, and would still permit the loudest passage of all tracks to play at a consistent level (32767). It would be perfectly reversable.

A scalar multiply would munge the track dynamics - it would effectively be a simple expander. Is that the case?

[jhenderson01075]

Re: How is volume normalization implemented?

Sorry - I understand now.

[adaywayne]

Re: Reverse volume normalization?

Unless the DMC normalise functions uses adaptive normalisation, theoretically you could get each track back to it original volume. The problem is that you don't know what that original volume was!.

Since you used normalisation on a batch of tracks, each track was "normalised" so that it's peak amplitude was a certain value (probably -1dB =~89% from the max of 0dB). So now, all your tracks have the same loundess at their peak value.

You can lowere these peak values track-by-track using a normalisation program that allows you to set the maximum decibel level (for every 6dB reduction you would halve the signal voltage). But since you don't know the original levels, you would have to rework each track using your ears as a judge of what "sounds right" to you. I think you could also use the Volume Quieten feature to achieve the same result. Hope this helps.

[petriburg]

Re: Reverse volume normalization?

There's a chance you might find this little free application useful, jh - I use it frequently to very good effect: http://mp3gain.sourceforge.net/faq.php

[neilthecellist]

Re: Reverse volume normalization?

Also, on a side note, check out the other products and projects in progress at SourceForge. They seem to have everything open source that caters to your audio/video needs.

[JethroUK]

Re: Why not?

To undo this process, why couldn't I scan the track to determine the minimum amplitude present - call this Tmin.....
What's wrong with this approach?

because it assumes the normalised track still contains the original max/min amplitude - which it doesn't - no more than a cropped picture retains what was cropped - the information you need simply isn't there anyomore

[adaywayne]

Re: Reverse volume normalization?

But if the tracks came from CDs that you still have, you could re-rip them and then find the originalpeak volumes. Painstaking, but at least you would not have to reburn.