Competitive class D amp suggestions

Ralph your tutorials are helpful!  At lease i understanding now better what is or can be happening with the sound delivered by audio equipment (why knows about electronics may also understand why is this happening). I still am not sure about some basic things. Now i suspect that the "higher order harmonics" are not second and third order  harmonics but 4th, 5th etc order harmonics (just to clarify, in my earlier posts i referred to "higher order harmonics" as the second and the third order ones!). Do 4th, 5th etc order harmonics also exist? Is the goal then to suppress 4th, 5th etc order harmonics with the second and third order harmonics, or also suppress the first order harmonics ? Why a high distortion in the first order harmonics cannot suppress the  4th, 5th etc order harmonics?

Independently of what is the answer, it is clear that an average of  some order harmonics and hence THD makes no sense (see my earlier posts) merely because it does not take into account the rules of acoustics.  

This allows greater transparency (since distortion obscures detail) yet the same kind of smooth mids and highs you associate with a really good tube amplifier- IMO, the best of both worlds.

I did not understand that. Are you saying that by obscuring the details greater transparency is reached ? 

@twoleftears this diagram, a proof of a nearly the same behavior of the  second and third harmonics is nice to see.

I still am not sure about some basic things. Now i suspect that the "higher order harmonics" are not second and third order  harmonics but 4th, 5th etc order harmonics (just to clarify, in my earlier posts i referred to "higher order harmonics" as the second and the third order ones!). Do 4th, 5th etc order harmonics also exist? Is the goal then to suppress 4th, 5th etc order harmonics with the second and third order harmonics, or also suppress the first order harmonics ? Why a high distortion in the first order harmonics cannot suppress the  4th, 5th etc order harmonics?

Let's be clear about something: 'masking' is where a louder sound (like a 2nd harmonic) can obscure a quieter sound (like a higher ordered harmonic). "Supress" suggests reducing the harmonic. So the lower orders do no suppress higher orders, but they can mask them if their amplitude is high enough in relation to the higher order(s) to be masked.

The higher orders are the 5th and above.

Are you saying that by obscuring the details greater transparency is reached ? 

No. I am saying that with lower distortion there is greater transparency; distortion obscures detail.

@twoleftears Interesting. That 18th harmonic (9KHz) looks increased. There also appear to be some intermodulations present (inharmonc; not positioned directly on a graticule or directly in the middle of two graticules). 

@niodari The first harmonic is the fundamental frequency of the note itself.  So that's the big spike to the far left.  Thus the other harmonics begin with the second.

The reason why the same note/frequency played on a violin and a clarinet sounds different is--simplistically--because different instruments produce different combinations of harmonics... rather like different models of amplifiers!

@snapsc 

The interesting thing from the March Audio review/test is that although the distortion is very low, the remaining distortion is mostly 2nd and 3rd.  The question  becomes "although it has great bass and an extended top end, is it musical"...or is possible that the distortion possibly too low for optimal musicality?

They sounded pretty darn good and musical when I heard the older 120W/ch version.
But I am more in the camp of “give me a wire with gain”, and not in the “spice to taste” camp.
Did hear some Devore O/98s with a Jadis that  sounded nice in LA (SoCal). I did not bust out the iPhone for an SPL reading, but they sounded loud.
They were musical, but not overly quiet in the “low distortion” way.

Horses for courses I suppose??

And as Ralph says here:

Most of them tend to have unmasked higher ordered harmonics at a low level, and because the ear uses the higher harmonics to sense sound pressure, its keenly sensitive to their presence! Also because the ear assigns a tonality to all forms of distortion, this causes most of said amps to sound harsh and bright even though they might have less higher ordered harmonics than a tube amp! This is how important the masking that the 2nd and 3rd provide can actually be.

The speaker (and amp) had a quietness about them.
(And the speakers having low distortion is likely a very big part of that.)

Historically I have usually found it rare to find quiet speakers. It is always a sign that something magical is happening.
I usually find this when I cannot hold a conversation and bust out an SPL measuring app and find it is playing 90-100 dB(A).
But it does not sound as loud as a system playing at 80 dB(A) in a somewhat perplexing way.

I only have found that happening when the speakers and amp have a low distortion, so I have no reason to suspect anything else than what @atmasphere is saying about “the ear” using the harmonics to determine loudness as being likely true.

Personally I do not likely opt for musicality via high distortion over having low distortion electronics and drivers in a speaker that is also not plagued by resonances. While both can sound good with most music… it just seems easier to get good piano and vocals out of a system that is lower distortion and more free of resonances.

But, then again… I have only heard a limited number of systems, and never heard Atmasphere gear in person. I am intrigued by his electronics… so it is (IMO) a low risk decision.
Similarly with the MA gear, it measures very well… and… I have heard it and it also sounds very nice.

Ralph, thank you for the explanation. One thing I’m still not clear about is why people describe class a and high bias a/b as being warm sounding especially if their overall distortion is on the higher side?