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In Reply to: I'm very confused about mosfet vs bi polar transistors posted by Rudi on April 18, 2002 at 13:40:08:
I think tubes do sound different and better. Some say this is just because of their distortions, but I think we don't have sophisticated enough measurement techniques to make that judgement, and even if it is correct, who cares what the reason is -- they just sound better. Fuller, easier on the ears. You can get plenty loud and funky with tubes -- Jimi Hendrix could tell you if he were around. But I admit you are talking a lot of extra hardware and hassle to get the wattage you want.The reason I question modern measurement techniques is we don't seem have a way to measure distortion on a complex musical signal. Maybe ten years ago I read an interview with an amplifier designer, Richard May, where he said that you can't predict the distortion on multiple tones from the distortion when only one or two frequencies are played. With today's digital signal analysis techniques perhaps you could, by sampling the output and spectrally decomposing the difference from the input, but I don't see where anyone has done this. Have they?
Follow Ups:
The reason you can't predict distortion based on single tones is because when you get multiple tones, you get cross-modulation/intermodulation, which is a completely different beasty. So he's right.
Audio equipment has, among electronic engineers, a lowly position in the scientific scheme of things. These empiricalists like to design "instruments" that have scientific application. And most of them think that audio equipment has such limited bandwidth that most any circuit should suffice. They are about as far from experiencing the joy that a serious audiophile experiences as one can get. They can't see the forest for the trees and consider the current audio happening as wags of the idiot fringe. The audiophile, it could be argued, can't see the trees for the forest. Engineers fail to grasp that audiophiles are deserved of and are entitled to components as high in quality as their so called "instruments". It would be wonderful if we could work together but mankind loves to segregate into camps and throw barbs at one another. But back to your question about distortion. It is my opinion that there are simply too many distortion mechanisms out there working against an audio signal to take all into account. I believe we've been looking at an audio signal only in two dimensions. It's like looking at a cliff on the surface of the earth from directly overhead in an airplane. We can't see the protrubances, the conglomerates, the chasms, and every nuance of the cliff until we see it in three dimensions and up close. With computer proliferation we are just now getting into 3D waterfall displays that I feel are going to re-write the way we measure distortion. The best! James
Journal of the AES - Table of Contents
2001 November, Vol 49 Number 11Multitone Testing of Sound System Components-Some Results and Conclusions, Part 1: History and Theory
Eugene Czerwinski, Alexander Voishvillo, Sergei Alexandrov, and Alexander Terekhov 1011
Evaluating nonlinear distortion in audio equipment, most notably loudspeakers, has been a constant topic of discussion because of the lack of progress in finding objective measures that correlate with subjective judgments. A comprehensive review of the literature spanning over 100 years illustrates the subject's intractable nature. A more formal analysis then leads to the conclusion that a carefully constructed multitone signal both simulates real music and allows for a mathematical theory that predicts the intermodulation products. This provides the basis for transforming the distortion products into compact metrics. THD is a useless metric.
1st part:
Over 100 refs, (including Risch multitone test) mentions Thorstens’ favorites: “noise fill” tests
Emphasizes multi-dimensional nature of distortion, shows THD just don’t do itin 2nd par: measured multitone distortion in horn drivers
Yeah, but they didn't use my recommendations for assuring that the primary tones do not step all over some of the distortion products.
An easy thing to avoid, once you know about it.I get the impression that this would have been conceding something, or somehow felt as indicating that their research was not as good as it could have been. Folks just love to have their proprietary test signals.
I spoke with Audio Precision, and they wanted to stick with their proprietary multitone, rather than explore more advanced options.
Their AP gear can be programed to do my type of multitone versions though, for those that have an AP laying around.Oh well, the info is out there, and some folks are using it even now.
If anyone is interested in the Phi Spectral multitone info, also known as:
AES preprint #4803, " A New Class of In-Band Multitone Test Signals", contact me via e-mail.
Jon Risch
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