Isn't there some way you could calculate the signal density you'd need in any of PDM/PWM/PCM to roughly equate to the quality of signal reproduction of a given tape media, given known tape surface/speed/magnetic density?
Anyway, you could do the work to work out the bit depth/signal rate you'd need to equate to reproduction of a given fluxdensity/recording rate. I would bet the numbers for classic PCM/PDM devices line up surprisingly close to certain tape systems.
On the flipside, once you know those numbers, you could also calculate what the expected analog equivalents could be, sample existing analog media/playback systems and use those to systematically characterize their quality, instead of going by earfeel, as it were.
