Mark,

"Are there any sources of square waves in natural sounds? "

Not that I know of. Instruments all produce sine waves.

"eg isn't that just some academic brute force test to show a "weakness" in the format?"

It shows bandwidth (and timing), but one needs to really understand what a square wave is to understand why that is. Along with capturing the harmonics they also need to preserve the phase between the fundamental and the harmonics. If phase is altered that will show up on the scope too as a corruption of the square.

"And with Meridian speakers topping out their frequency range just above 20kHz (and with most of our hearing topping out around 16k)"

Right, a speaker isn't going to reproduce a 10kHz square wave at all, it would look horribly distorted. The speaker don't have the bandwidth or phase linearity to handle this you would just get the fundamental sine wave. And like you said even if the speaker could handle it we wouldn't hear the harmonics anyway as that is beyond our hearing range, we would just hear the fundamental sine wave at 10kHz.

"all we're essentially gaining from the 48/96kHz modes are increased dynamic range?"

The difference in 48kHz to 96kHz has nothing to do with dynamic range. It just increases the ability to capture from just below 24kHz to just below 48kHz. Dynamic range in the source would be increased by going to more bit depth... 16bit to 24 bit for example. Most people don't have systems (including the room and its noise floor) that can deal with the full dynamic range of a 16bit system and nobody has a system that could handle actual 24 bits of dynamic range. 24 bits of true dynamic range would be 144dB. To reproduce that if one had a room with a noise floor of 0dB and you matched the noise floor of the source to the noise floor in the room the loudest sounds would be playing back at 144dB. Very few speakers could play that loud and your hearing wouldn't last very long at all if one tried for this... roughly the same SPL as standing a few feet away from a jet engine. 16 bit gives 96dB of dynamic range. Again in the 0dB noise floor room the max volume would be 96dB which is possible. In a room with a 40dB noise floor if you don't want to loose source signal in the rooms noise floor the max SPL would need to be 136dB... again not really possible. If you limited playback to say THX Reference level of 105dB (per speaker) with that 40dB noise floor in your room your overall system is limited to about 65dB of dynamic range... about 11bits.

Best way to increase dynamic range/resolution of a system... lower your rooms noise floor.

Shawn

.