Class D Technology

Switched voltage 50-80V represent the highest output voltage.  They show switching noise riding on a very small signal.  This signal of 1V peak represents 63mW of the root frequnecy + harmonics on the 8 ohm speaker.

Sorry your wrong kijanki, the switching frequency to signal ratio follows the signal level in a proportional manner. and that 20% pod SF noise in the links I provided above, the SF noise does not disappear at certain levels of playing, it stays proportional to the level your playing.

And I didn’t ask you about tweeters playing 500kHz, but seeing you mentioned it, ask the poor sod I had to replace both the Wilson 8’s tweeter diaphragms on, because they were blu’ed with heat abuse from this 500kHz noise. They still worked but never sounded quite right, but they did when I replaced them. BTW he won't use a Class-D again, until he's convinced that the SF noise won't harm his tweeters again. 

Cheers George

You might damage membrane from overheating, but most likely not from 500kHz switching frequency. As for switching frequency level following signal level - your understanding of class D output is poor. Amount of switching noise is constant independent of the signal level and in your Stereophile example equivalent to power of 4mW (of inaudible frequency) on 8 ohm speaker.
This switching noise is only dependent on the switching frequency and the filters cutoff frequency. Amplitude of the music signal has nothing to do with it!!! If anything, switching noise at extreme duty cycles will be lower. Signals of 10% or 90% duty cycle represent lower amplitude (in comparison to no signal represented by 50% duty cycle) of the root frequency (500kHz) and a little bit higher harmonics. After filter amplitude of 500kHz will be lower (and not higher) at high music levels.

I’ve seen it on the scope, with Nuforce 9se V3, you need to see it for yourself.
Lower or raise the signal level at the same frequency, then increase or decrease the scopes sensitivity to the same visual appearance, and you’ll see the SF noise remains the same. Forest and trees sunshine.

BTW it was this amp that gradually cooked the WP8’s tweeter voice coils, and the owner (a reviewer) was never abusive with high level, if anything he was anal about playing too loud, he now ones Gryphon Antillions, and has not looked back at Class-D.
Maybe in the future when they can rid this SF noise demon totally without any effects down into the audio band, even he concedes to this after what he went through.

Cheers George

I'm not sure what NuForce are doing.  It is possible that they adjust supply voltage to signal level, but that would only mean much lower noise (than for instance Icepower)  at low signal levels.  Noise level at max loudness would be the same as for the amp that doesn't do that (assuming same switching frequency and the filter) - equivalent to about 4mW on 8 ohm speaker.  Icepower doesn't adjust the rails and I'm pretty sure Hypex uses constant supply voltage.   With constant supply voltage amount of switching noise at 90% or 10% duty cycle would be most likely 1/2 or even 1/3 of the one at 50% duty.