Normalize and DC offset correction

[steve]

@edgar-rft

@steve

…removing a DC component should be unnecessary…

…but only in theory, I’m often enough forced to work with bullsh**t equipment, where removing unwanted DC is the most important function of all.

Another problem with bullsh**t equipment is that the offset may not be constant DC but rather a slowly drifting offset. I think this is a case for offering more than one type of offset correction (probably not as part of the Normalize effect but rather as a separate “Offset Correction” effect). A drifting offset is subsonic AC rather than DC, so a high-pass filter is required to remove it rather than (only) DC offset correction, but this is drifting off into a different topic.

@edgar-rft

The point is that I never have found a single use-case where normalizing without removing unwanted DC ever made sense. But it’s also not a good attitude to bigheadedly say that nobody will ever need it. It often happens that one day I need some particular settings and the next day in a similar situation I need exactly the opposite. It’s difficult to say what is “unnecessary” and what not.

I’ve been thinking hard for an example of when Normalizing without removing DC makes sense. The only example that I can think of is if Audacity is being used for processing/editing non-audio signals (which some users do use it for). So even though it is very much a fringe case I think that DC correction should be retained as an option.

There is also the issue of speed.
In the Audacity effect, calculating the DC offset requires looping through the samples in an analysis stage and this definitely slows down the processing (by about 25% on my computer). There’s a comment in the Audacity Normalize code:
“// we don’t need an analysis pass if not doing dc removal”
So it looks the intention is to minimise processing time.
In the Audacity Normalize implementation calculating minimum and maximum sample values is (so I’ve been told) a lot faster than calculating the offset.
In Nyquist, using the “integrate” function there appears to be little if any speed penalty in calculating the DC offset.

@edgar-rft

But currently there are some nonsensical settings in the plugin like “neither remove DC, nor normalize” what in end effect does nothing… ???

It does seem nonsensical to include an option to disable normalizing in the “Normalize” effect
I think that this possibility exists because there is no separate “Offset Correction” effect. It would imho make a lot more sense for the “Normalize” effect to always normalize (with DC correction as an option) and if offset correction is required without normalizing then an “Offset Correction” effect should be used.

We see quite a few posts from users that have DC offset but have not found the correction tool. If offset correction was a separate tool then it would be a lot more visible as well as resolving the nonsense of the “do nothing” option in Normalize.


Thanks for the Normalize-2.ny code. It’s very instructive.
It also very clearly indicates the bizarreness of normalizing without DC offset correction.
(if normalize without DC correction → normalize the AC signal and add the DC offset)