Please help me understand


There are two concepts I've never been able to reconcile. How is it possible for different amps to have similar distortion levels (inaudible), yet still have what audiophiles might describe as a "tonal signature". In other words, how is it possible for an amp to have a perceived "warm" or "bright" sound, if it's accurately reproducing the input signal? It seems to me that all high quality, properly functioning amps should sound the same. If they don't, them some of them aren't doing their job very well.
danoroo
Why not just believe what you wish, but when you try to justify your beliefs it gets kind of silly. It's obvious that all the so-called analogies are not applicable. To try and discredit science in order to say one amp sounds BETTER than another, is just plain silly. The point is conceded, You can hear it all.
I hate to be the boring techno person here, but Bob Carver was right. all electronic circuits have what is called a transfer function that determine what the circuit will do over frequency with specific voltage/current variations. Unless the amps in questions employ exactly the same circuitry, there is no way on this planet that they will operate or sound the same. If you look at the results of the circuit's transfer function you will see exactly what I am talking about. Bob Carver did something very cool and tricky years ago. He got a really high end tube amp (don't remember the manufacturer). reversed engineered it and actually determined the amps transfer function (this is literally an equation showing the voltage in/out characteristics showing resistance, capacitance, inductance impedances for the circuit) then he managed to actually design an amp with the same (or close to it) transfer circuit) to show that 1) he could do it and 2) he could do it to sound just as good or better than the other amp for less cost) and guess what? he did it. really good amp. My point is that each and every electronic circuit when completed has a vo/vin transfer function. So if you computerize the transfer function and run signals in over frequency, you will see the amps characteristics are totally different over frequency and phase. They couldn't possibly be the same. not a chance. Also, I disagree that measurements have limited use. If you don't use measurements, there is no way on this planet you could actually design any electronic equipment. You design amps based on detailed specifications, as I have mentioned several times previously, such as phase, frequency response, gain, input/output impedance, load handing (what loads are it supposed to handle over the power band width and frequency), etc. once designed and built, guess what? you have to put it on a test bench and ....... measure the responses to see if the amp performs based on your actual design specifications. Any yes, we can measure for sound of particular amps. This is definitely where transfer function responses come in. but, this is not cost effective and unless it is a military device, no way on Earth will this type of design be done for amps. But make it worth someone's while and specifications and measurements will be developed (already are) to tell you how it will sound. Right now it is simply not worth it to spend the time and extreme money to do this. Because audiophile and music reproduction is not large enough for scientist to invest that amount of time and expense to do this. But, let me back up here, there are some audio manufactures that know what particular circuitry does sound like, Nelson Pass, and many others, and what they do is incorporate that particular circuitry in their amps all the time. The only time they change is when they develop new circuitry and amps and listen for some time and like the sound over the previous circuitry. this is physical measurements using human ears, not paper and pen or computer measurements. But don't think for a moment it can't be done. This is a physical universe, of course it can be measured. We determine many things and science by reverse engineering. I thought Bob Carver's approach for that particular tube amp was great.

enjoy
I do not think it is true that the human ear is more sensitive than any measuring tool. But what is often claimed is that while some levels of distortion are measurable, it is provably inaudible.

My argument would not be that such a claimed level of distortion is in fact audible, it would be that we are not appropriately measuring distortion through the entire system, and that the THD specs often listed do not accurately represent real world system wide distortion, not least of which being the interaction with a real world speaker.

Two cars may have an identical 0-60 mph number in a straight line, but once you get on the track, things like wind resistance, weight distribution, front versus rear versus all wheel drive, gear ratios, coefficient of friction, etc all come into play.

THD as a standard measurement does an ostensibly admirable job of presenting a metric given a very simple and constrained model. But it does not account for the bends on the road.
"If i take a vision test and have 20-20 vision does that mean I can see colors?"

no, but you could take this test and check if you do:
http://www.opticien-lentilles.com/daltonien_beta/new_test_daltonien.php

each manufacture when designing amps/speakers/preamps etc - are largely basing their testing on measurments and actual listening - now, depends on the equipment they have available
(the rest of) - it might sound perfect with what they have.
But it does not mean that it will sound same with other combination (for example Accuphase preamp with McIntosh power amp and reverse - just does not sound as good as manufacture match - if manufacture match, then sound is good on both but different). Simply speaking - each equipment has some kind of "equalization/sound proceesing" circuitry that will effect actual output. After that is up to the buyer to decide if they like it or not...
There are sound correction device (like McIntosh MEN220) that tries to compensate for all the equipment/room and make the output more listener "friendly" - but in some cases it can not.
As mentioned before about Bob Carver - yes, it is possible to make 2 different amps sound exactly same using different components - but why? if it was the case, then we would not need all the audiophile forums and discussions.....
so trying to achieve perfect sound by swapping components - it is a endless job, every time we change some component, we gain somewhere and loose somewhere else - but all this keeps audiophiles busy and generates nice profits for manufactures