Our ears hear more bass and treble as the level goes up, so louder reads as fuller and clearer. That's why an EQ boost or a compressor's make-up gain can sound like an improvement when it's only a level change.
How do you compare fairly?
- Measure both versions' loudness in LUFS (short-term or integrated over the same passage).
- Trim the louder one down until they match within about 0.5 LU.
- Flip between them on the same passage, several times, ideally without looking at which is which.
How does Ovrtone do it?
When Ovrtone's engineer makes a bigger change, it comes as a plan you can flip between: A, your mix as it is, and B, the plan, played at the same loudness. Nothing in the plan is kept until you apply it. Every change, planned or not, is one undo step.
Sources
- ITU-R BS.1770: how loudness and true peak are measured, the method behind LUFS.
- EBU R 128: loudness normalisation, with LUFS for loudness and LU for the difference between two loudnesses.