Opus codec and why its magic

There’s no shortcuts when evaluating perceptual codecs. Those who have worked on codecs all wish there was, but there’s not. Their strategy is to hide noise where it doesn’t matter, both in time and frequency domain. So looking at the difference in time or frequency is interesting, but won’t inform about perceived quality. The open-source codecs tend to develop *and* evaluate/compare using a psychoacoustic model (PEAQ, etc.). That’s cheap and worthless, it’s just a fancier way of comparing differences. Modern codecs are at least as sophisticated as the perceptual models in these evaluation methods, so not the right tool for the job.

The only way to evaluate these is by blind listening tests (MUSHRA, ABX, etc) with enough listeners. And with high rates, the first step is to find critical material (stuff that is hard to encode). Examples that come up a lot are applaud (try stereo too), castanets, speech (German is tough to encode for some reason), bagpipes and other tonal instruments. These stress either the time or frequency behavior of a codec.

Have fun, but accept that this is hard work.