Humans can hear up to 28khz when paying close attention. "CD Quality" is slightly below the threshold of hearing, at a point where most people don't notice the difference or care to notice the difference.

It's also somewhat poorly-defined, because "CD quality" can mean lousy mid-range performance when rounding 24-bit to 16-bit, or high frequency hiss when noise-shaping 24-bit to 16-bit.

So "CD quality audio" is quite a degradation when you listen in a 100% quiet room with expensive speakers and your full attention.