....
Pass makes no statement implying that listening alone could be useful in developing an amplifier (or any other piece of kit). Instead, the article mostly explains in terms of simulations and measurements the effects of non-linearities concerning the input signal (explicitly leaving othe non-linearities aside).
All the graphs show data for zero feedback scenarios, only. To learn more about why negative feedback is so helpful (and so misunderstood), here is a slightly more recent article by the best known developer of the most accurate class-D amplifiers in the world, Bruno Putzeys (Phillips, Hypex, Purifi, Kii Audio, ...):
True.
I've read Bruno extensively too... good reads. He also listens.
It is true that our current measurement techniques do not quite explain what we hear. At least we don't know all of it.
IMHO, the FCC standard of quoting power at a given THD is incomplete nowadays, since we now know that not all orders of harmonic distortion have the SAME effect on our perception. We can tolerate a lot of 2nd order but very little 3rd, and 4th yikes. Two amps with the same power rating, one with 1% of 2nd THD and the other with 3rd THD will sound extremely different. Why? Well, we don't know why, we JUST know. So, the ratings should reflect the harmonic distortion spectrum...
Eg:
25 watts into 8 ohms from 20-20Khz with HD at (0.5 / 0.1 / 0.0005 / 0.000001 )% where we define the harmonic distortion at the 2nd, 3rd, 4th and 5th. Nevermind whether it's positive or negative....
Indeed, a little bit of negative 2nd order harmonic distortion, aka "the sugar" makes things sound better. Go listen to a bridged amp, with very low 2nd harmonic distortion and you note how "lean" it sounds. First Watt's SIT1 actually had knob to adjust this. In some of my amps I've thought about specifying such a knob in the front panel.
I think what separates Pass from many is that he knows from experience how to achieve a given sound by design. He purposely "voices" his amplifiers to sound good not to measure good. He's also a funny guy... but then, he is at heart a physicist that likes red wine.
Bruno is there too. He knows how to create a sound he wants. In his case he goes for very low distortion, extremely low output impedance and the resulting very high damping factor. Getting away from an integrating output filter.
What's fascinating is how Pass is old school linear mathematics while Putzeys uses numerical analysis.
Both are fun to read...
What can active speakers do that passive ones can’t? Impulse response, impulse response, impulse response, says Bruno Putzeys. That, and their sheer practicality, makes them the wave of the future.
pmamagazine.org
While we're at it...
What I really want is a homogenous WiiM Home that operates equally across all hosting platforms.
benchmarkmedia.com
