
Ethan Winer
Acoustics Expert
1) Signal-to-noise ratio alone is not bit depth, and there is no easy comparison between analog and digital in this regard.
I know you're a smart guy, so I'm surprised you don't understand that s/n is directly related to bit depth. Monty even proves that tape hiss and digital hiss (without noise shaping) are the same:
Monty Montgomery explains digital audio
2) With noise reduction of various types, analog tape, even many cassette-based systems can meet or exceed the practical signal-to-noise ratio of 16-bit and even 20-bit digital devices. The theoretical S/N ratios of given bit-depths do not occur in real digital devices.
Bobbsy already explained that this is incorrect. It's common, especially among audiophile types, to hold up bogeymen such as truncation distortion and jitter as damaging, even though they're 90 and 110 dB below the music. But with analog tape noise reduction, the tape hiss is never farther below the music than the inherent s/n affords. Yes, the noise pumps up and down with the signal level, so in practice tape noise reduction reduces noise subjectively. But the underlying s/n is not really improved.
3) There are many other benefits to higher bit-depth, not the least of which is more effective error correction, which reduces the number of unrecoverable errors in a digital sample.
Dude, whatever you're smoking, please pass some over this way.

If anything, having more bits in a data stream only increases the odds of bits being dropped. But how often does that happen between a computer sound card and the hard drive? Answer: Never. The only thing bit-depth affects is s/n. If you have any evidence to the contrary I'd love to hear it. But you'll have a very hard time disproving Shannon et. al.

--Ethan