Class D Technology

The difference, way back when, was in the highs, where Class D was kind of grainy compared to a single-ended transistor amp used for comparison.

Talking about Spread-Spectrum during cold war could put you in a prison (top secret).  Today all CDMA cellphones (Verizon, Sprint etc.) use spread spectrum.  It is interesting application for class D, especially when receiver reacts only to average value (no keying needed).

There is about 1% of switching voltage noise on the speaker cable

You need to rethink this.
Look at the switching noise ringing on the test square waves Stereophile show when they don’t use their special Audio Precision’s auxiliary AUX-0025 passive low-pass filter to hide the switching noise ringing from view.

This is what’s on the speaker cable on the $7K Anthem Statement M1 monoblocks, and it more like 20% of the wave form.

Without Audio Precision’s auxiliary AUX-0025 passive low-pass filter
http://www.stereophile.com/images/1212AM1fig02.jpg

With Audio Precision’s auxiliary AUX-0025 passive low-pass filter
http://www.stereophile.com/images/1212AM1fig03.jpg

Cheers George

Stereophile test shows about 0.5Vp-p  - that is about 1% since switched voltage is in order of 50-80V.  It comes from the fact  that output filter is 2-pole making it -40dB/decade while switching frequency is about decade above filters cutoff frequency suppressing noise by 40dB.  -40dB is 1%

As I posted before, speaker cables have no chance to radiate for many reasons.  Tweeter won't play 500kHz,  not only because of membrane inertia but also because of its impedance rising extremely high.

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.