This demo lets you interactively explore the effects of quantization on different audio samples.
Press a button to play one of the samples, and then use the slider to adjust the audio's bit depth on the fly.
I've found that distortion is almost inaudable if you use 11 bits or more, and it becomes really noticable if you go lower than 9 bits.
bit depth
16 bits
These audio samples are (obviously) not mine; they're being used under fair use for educatonal purposes.