I changed to normalizing to a custom dB or normalizing to RMS, peak RMS, or overall peak RMS.
I generally select all 4 channels to normalize at the same time during this process.
I can not figure out why I get RMS and VU levels in the red AFTER these processes.
On Peak vs RMS-
An RMS measure approximates
perceived sound level. It reflects a specifically formulated "averaged" value across peaks and troughs over short duration which more closely corresponds to our
perception of loudness. RMS is an intentionally "slow" measurement, where as Peak is an "instantaneous" measurement. Rapid transient peaks produce brief high level values but do not sound "loud".
With simple periodic waveforms such as a straight sine wave, the relationship between RMS value and Peak value can be calculated and is predictable.
But audio produces complex arbitrary waveforms and is
not predictable in the same way, so with music the relationship between peak and RMS values is not constant or known without measuring. If you choose to normalize based on RMS value and choose an overly high normalization target value, the waveform will be amplified such that the highest RMS value equals your normalization target, but the peak values will exceed 0dbFS.
To avoid that, if the goal is getting close to but not exceeding 0dbFS, normalization based on peak value is more appropriate than RMS. In that case the waveforms will be amplified such that the highest momentary peak matches the normalization target but RMS may vary between channels. If the goal is getting all the sources to similar loudness levels, then RMS normalization is appropriate, but each file can then have different maximum peak values and one does not know exactly what the maximum value might be.
You may be well aware of all this already. I just wanted to clarify these fundamentals.
How it applies-
We normalize or adjust gain manually to optimize the level of a file so that the signal fits comfortably within the dynamic range of the medium. This clearly applies to the output format where we manipulate the master-bus output level to get the highest peaks relatively close to but not exceeding 0dBfs. Yet prior to that we may need to manipulate levels for additional reasons: Getting each raw file to a reasonable working level within the mixing/editing software, getting approximately similar levels across all channels prior to mixing them, and making mixing decisions which will precisely determine the level relationships between channels, which we wish to preserve from that point onward.
If you are recording in the traditional way such that the highest peaks range between, say -12dBfs and -3dBfs, you don't really need to normalize the raw files prior to mixing them. But if you had very low recording levels in one or more channels, or if you are using a 32-bit-floating point recorder where you aren't manually setting input levels, you'll want to normalize to some reasonable starting-point level prior to mixing. That simply gets them all in a good working range within the mixing software. Once you start mixing, do so by ear - checking the balance of each stereo source in isolation and adjusting that if necessary, then adjusting the balance between each of those pairs and individual channels. At this point you want to preserve the overall level relationships between channels based on your mix choices. Once the mix is done, you might peak normalize the 2-channel output (or manually adjust gain, or limit, or some combination of these things) to make sure the peaks are sufficiently close to 0dBfs yet do not exceed it. But you don't want to normalize each channel individually at that point as doing so will change the mix level relationships, and will affect mix features such as threshold settings in an unwanted way.
Specifics-
I changed to normalizing to a custom dB or normalizing to RMS, peak RMS, or overall peak RMS.
Custom dB presumably normalizes based on the highest instantaneous Peak value found within the range (typically the length of the entire file).
RMS presumably normalizes to the highest RMS value found within the range (typically the length of the entire file).
I don't know what
peak RMS or
overall peak RMS mean or refer to. Those are confusing and potentially misleading terms to be sure.
..any clue why my normalization process(es) is/are taking my RMS and VU values over 0dB even though I assume they would not?
If you normalize two or more raw files to RMS=0dBFS prior to mixing them, the RMS sum of those files will exceed 0dBFS. And even if RMS normalizing to a few dB below 0dBFS, the RMS of the sum may still exceed full scale. Yet even if levels above full scale are occuring within the mixing program, it's not necessarily a problem at that point as long as long as arrangements are made so as to peak below 0dBFS prior to output. This is because all modern mixing programs use 32-bit float internal calculations which allows them to handle levels above than 0dB internally without clipping. It's really only when writing an output file that the signal must be properly "fit to the output file limits" again. However, it's still best to maintain good levels
within the software so that various thresholds and other tools such as a limited amplification ranges or fader movement ranges all work correctly.
Even though modern tools make it less critical to keep an eye on than it once was, good gain staging remains fundamental though all phases of recording and production.