CDs are limited to a 90 db
CD has a ~93 dB theoretical SNR, but noise shaping pushes most of that noise above 16 kHz where the human auditory system isn't so sensitive. In practice, CDs can be mastered with 120 dB of dynamic range in those frequencies where it matters. It appears TigerPlish is referring to a 24-bit processing chain, which reduces the noise that each generation of digital signal processing adds, resulting in a cleaner 20-bit master heading into the 16-bit noise shaper. Monty explains.
Or look at it another way. Imagine a 1-bit format that uses heavy dithering to represent signals using pulse density modulation. How much dynamic range does a 1-bit signal have? If not much, why would Sony have chosen 1-bit PDM at 2.8 MHz for SACD?
LPs are limited to 60 db but oddly I have several LPs with more dynamics than their CD counterpart.
That's because level compression in LP mastering works differently from CD. LP uses RCA Victor's New Orthophonic preemphasis curve, which allows bass to go louder than treble, while CD uses no preemphasis.
But the point is, we're not talking about classical music with a 72 piece orchestra, we're talking about what's on the radio worldwide.
I listen to NPR's classical station, you insensitive clod! :p But seriously, recordings destined for pop radio are mastered with very little dynamic range because they have to be audible over a motor vehicle engine that allows very little dynamic range.