Class-D amps - a different re view

Muralman1, you're in a good position to record that viola- and then play it back. *Thats* what I'm talking about. You already *know* what the instrument sounds like.

That's the technique I use when I am auditioning anything- speaker, a tweak in one of our products, a class D ampilfier- whatever. Sure, I play a variety of recordings, but its always useful to be able to play one where you were at the recording session.

To address an earlier comment- the distortion that a tube makes is not something that is cast in concrete. I have found that quite a bit rests on design consideration as well as materials. Not all tube amps have a predominant 2nd order harmonic- that's really a character of SETs. Push-pull amplifiers have even-order cancellation.

If you look at the distortion makeup of a lot of the class D modules, the distortion can be quite high for a 'transistor' amplifier. We have a module here that is 10% at full power. We've not measured the spectra, but I can tell you that the distortion is under 0.5% or so to about 50% of full power. The IM is actually higher than measured on our own production amps. Of the two, IM is usually more audible than THD. The appearance is very much (in the case of this module) that the ear is ignoring a lot of the THD, i.e. it appears to be even-ordered. IOW it seems to have a lot in common with SET amplifiers! I thought you might find that interesting...

By no means is the module that we have (Phillips) representative of the entire field. It would be interesting to see if there is a correlation either negative or positive with what we hear in these amplifiers as opposed to what is measured! A negative correlation, FWIW would put the behavior in the same realm as tubes, where much of the distortions made are ignored by the human ear.

Hi Vince, that's exactly my point. The sound of rosin for example is extremely faint and can be heard clearly only if you 'are' a microphone, or you are sitting/standing so close to the performer to be socially unacceptable under most circumstances. most concert goers will never hear the rasp of rosyn from the 4th, 12, 30th, or 50th row behind that plynth. . , particularly if they are surrounded by other listeners wearing sound absorbing winter clothing. Besides, what is 'real'? What I can hear when in a good day without tinnitus I can outperform audiometric equipment? or what's real is what the average middle age listener hears with a 12,000Hz cutoff, or what my dog can hear with a bandwidth of perhaps 50Khz. Or perhaps the perfect ears are those of a microphone? Which one? How sensitive? With ewhat dispersion, with what kind of bandwidth? Even the most perfect recording is by necessity just a cropped, filtered, an edited 'view' of reality containing selective enhancements. Nothing wrong with that, provided that we realize that our own perception IS NOT reality, but merely a useful and partial interpretation of it.

I have grown wearie of reading the black&white cartoonesque audio manifests of those who seem to be wanting to ram facile editions of some kind of Audiophile Pravda down my unwilling gullet. When I really want to hear the 'Truth' I'll find me a Church. . . for the time being, music and the quest for beauty may suffice.

11-16-07: Guidocorona
Hi Vince, that's exactly my point. The sound of rosin for example is extremely faint and can be heard clearly only if you 'are' a microphone, or you are sitting/standing so close to the performer to be socially unacceptable under most circumstances.

An excellent point!

Uber resolving recordings and uber resolving playback systems might get close to the truth of the sound recorded at 2-3 feet from the performer/instrument, but the presentation is unrealistic and unrepresentative of most experiences of live music.

Interestingly, I was listening to The Doors' "LA Woman" last night, and I could swear I heard the squeak-squeak of the bass drum pedal during "The Changeling". Very odd, and something that I never heard before. Not at all what one would hear during a live performance.

Tvad, I have a Royer's Microphone demonstration disc. It covers the different microphone positions, and their affect on the final sound. Recording is an art in itself.

On solo acoustic instruments, with a uber-resolving system, you can indeed hear the rosin's stickiness, and those faint bow angle tonal tickles. That is what I want to hear, and that is what I have.

Orchestral staging is quite different. I am careful to choose a volume level that is compensatory to the distance between my speakers, 7.5 feet. That puts me on first balcony.

Guido, I love your writing style. - read the above post. I have untampered recordings, and I love that. A close miced guitar is wonderful, because most of us have heard guitars up close. As annoying it is to hear the string squeaks you do want to hear the string windings when the player slides his/her fingers along them. When Kottke really gets going, his manipulations of each string and each fret are simply awesome.

People with poor hearing do miss a lot. I know fellows like that. Mids and lows are everything to them. I have that great recording, Windham Hill '84 on now. That is a good one for detail. During one song (on now) the drummer is constantly tickling the high hat. It is a panoply of high frequencies not enjoyed by the hearing challenged.

You know real when you hear it, regardless of your hearing ability. There are clues.