The Future of Audio Amplification

The switching frequency is at 450kHz, no tweeter could possibly reproduce that... Not that anyone would hear it, not even dogs.

You need to understand better, it’s not the switching frequency "so much" but the "output filtering" needed to get rid of it that ’s problem, which gives phase shift problems right down to 3-5khz (the mids and highs of the audio band). (That's why any complaints of Class-D is the upper mids and highs, never bass or lower mids).

If that switching frequency were to be moved up 3 x higher (like the $20k Technics SE-R1 does with the GaN transistors) then that "output filter" can be also moved up by the same amount, then the phase problems move up as well in the audio accordingly.
I would like to see 5 x higher.

Cheers George

Maybe that is what the class D amplifiers will be in 10 years more. Class D is evolving really fast. It is the future of audio amplifiers indeed.

Oversimplification is usually done by those who have had very little hands on tweaking of amps. I have been designing, modding and tweaking amps, etc. since the late 1970s. When you realize that every single part and execution effects the sound then just going after one measurement or whatever is just plain wrong. Most all of the class D amps till now have switching around 500K........and most use the same type of filtering on the output. However, they all sound different, including the highs. The Merrill probably switches at 500K yet no one says the highs are not great......same with this IceEdge amp.....super clean highs.....and same filtering. Other amps using the same 500K and same filter sound strident or rolled off or compressed in the highs......because there are so many factors that effect the sound. It is not one thing. It is not just the filter effects, it is not just the distortion measurements....it is hundreds of things that make the sound. I am not against wider bandwidth, GaNs, and better distortion figures. But these things will not bring state of the art sound by themselves. For instance, the stock IceEdge modules sounded OK when I first listened to it (all hardwired, no connectors)......but when I changed the fuse to a serious audiophile fuse I said.....Oh Wow....this amp really is good. Want to blow your mind? Damp the heatsinks on your big Class A transistor amps. If you run your fingernail along the heatsink and they sing, then you are adding that sound into the amp. Every person who has done this has heard the same thing.....way less "transistor" sound......which, of course, was really heatsink vibration sound being superimposed on the signal. My Class D amps will have every panel and the modules constrained layer or multiple layer damped.

Hello guys
I think the thread has gone to technical for me. 
Im not an expert, but I've tried some class A amps, SS and tubes, and now Im trying a Nord One UP NC500DM class D amp, wich has just replaced my previous beloved Line Magnetic LM-508IA class A valve amp (single ended 300B), wich had a VERY good reputation among audiophiles. 
Using both as power amps with the exact same system (a pretty revealing one) I must confess that Im blown away by the superior perfomance on "every" field the class D amp has against the 300B class A valve amp.
On every field Im not Just referring only to grip, dinamics and holographic sound, but also on some fields I thought were the 300B amp strengths like warm, delicacy, tone and texture. 
I still cannot believe the outstanding perfomance of this Great class D amp, even its not burned in yet as it only has about 30 to 40 hours playing and it should get "much" better. 
Its incredible! It cost less than a half, weights about 30 kg less, produces considerable less heat and I dont need to spend on valves ever again.
I was a valve amp lover, but now I found a much better and cheaper solución for my system.
To believe or not to believe. 

Ric, really good input (NPI) from you;) and likely why Peter Madnick's AA design got such rave reviews. Owning the DPA-1 (stereo amp) the only tim I notice glare is from poorly recorded discs. And yes, I recall ringing whn I had my KBA 75 with chassis long heatsinks

plga, lucky you. Is it the NC 500 Mk II?  I am close to pulling the trigger on a pair of Audio Alchemy monos for about the same money as the Nord Mk II. Not surprising, it's out of stock. Wish I could hear them. Im in S Florida

https://www.nordacoustics.co.uk/nord-one-se-nc500