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Old 19th April 2012, 10:08 PM   #4491
tvrgeek is offline tvrgeek  United States
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Quote:
Originally Posted by janneman View Post
Don't know about Philips in detail, but they were very conservative, more like "it measures great therefor it MUST sound great". They were at the time an engineers' outfit, not very good at marketing. Their video casette system was arguably better but lost from VHS marketing power.

A few years ago I spoke with the guy who invented the moving magnet cartridge, but Philips thought that piezo cartridges were all that would ever be needed. This guy went to work for Bauer at Shure and the rest, as they say, is history.
Sorry for rambling on like that...

jan
VHS won for one very simple reason: They were the first consumer unit with 3 hours and could record a full American football game. End of competition.
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Old 19th April 2012, 10:35 PM   #4492
a.wayne is offline a.wayne  United States
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THE PROBLEMS WITH MEASUREMENTS

All audiophiles should at least once bring an accurate sound-level pressure gauge into their listening rooms. This is especially important for those music lovers who listen mainly to acoustical music; classical, jazz, folk etc., like me.

After an evening of listening to different music and observing the meter, most audiophiles are very surprised at how low the dB readings are on the gauge; usually between 60 to 85dB. It will on occasion go lower, and only for extremely brief instances will it ever rise above 90db. Much more important than the pure numbers are the ultimate implications of all this. What do these surprisingly low dB numbers really mean for the on-going scientific and practical attempts of measuring a component's ability to reproduce music?

They are devastating, and here is why.

Let's start with a speaker of fairly high sensitivity, which is the trend these days and also what I recommend above. Let's say the sensitivity is 90dB/1 watt. This means that at an 80dB loudness level, this speaker is receiving a total of 1/10th of 1 watt of power from the amplifier. This is the point where most audio magazines stop measuring, but this is the exact point where they really should begin "fine measuring", because the 80dB is only the peak/accumulated loudness at that moment. All the real, fine musical details and information; the harmonics, decays, sense of space, dynamic inflections etc. are still 20 to 30dB (or more) below the 80dB peak.

What does this all mean?

The truly unique and distinguishing musical information is being reproduced with only 1/10,000 of a watt or even less power!

At a softer 60dB loudness level, which is not that unusual, the power level of even 1 Millionth of one watt becomes important! Which audio "tech/guru" or scientist measures what is happening in an amplifier from 100th to 1,000,000th of one watt?

The Answer: Not even one.

This same basic principle holds true for measuring preamplifiers, speakers and everything else. (It is also a very plausible explanation why some components appear to sound better after some "break-in".) Until it is possible to scientifically measure low-level musical information, we will have to trust our imperfect and unscientific ears and let them choose what component has the most "magic".

This inevitably brings us to the next logical and unavoidable subject.
-Salvatore
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Old 19th April 2012, 10:37 PM   #4493
a.wayne is offline a.wayne  United States
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Default MEASURING ULTRA LOW-LEVEL MUSICAL AMPLIFIER SIGNALS

"My name is Steve Keiser, the 'K' of B&K components, and presently design engineer with Luminance Audio. I have developed a measurement system which is able to quantify distortion levels at micropower quantities down to 1/1000th of a watt. These measurement techniques are unprecedented, and have revealed a number of revelations of amplifier distortion characteristics, at micropower levels, which are in direct opposition with traditional and scientific assumptions up unto this point.

The emphasis of my work is to definitively quantify low level signal linearity measurements of power amplifiers, and attempt to correlate these measurements with subjective listening results, as well as establishing the significance of low level distortion. Conventional test equipment generally does not resolve meaningful distortion measurements below 100mw, since the measurements become predominated by noise.

I have modified a spectrum analysis software program, which uses time-averaging to effectively cancel out noise products, leaving an identifiable signal and its related harmonics. This time-averaging approach is to identify extremely weak signals from spacecraft, amid a very high noise ambient background. Using this method, I am able to resolve a standardized total harmonic distortion measurement down to 1/1000 watts, and an approximate measurement down to 1/500,000th of a watt.

My measurement results oppose common engineering supposition, in that it is commonly believed that very low signal linearity is essentially 'virtually perfect', and that only high level signal linearity is a relevant parameter. My measurements indicate exactly the opposite is true of this common held assumption, particularly for amplifiers employing solid state devices.

To give you an example: the Halcro DM58 amplifier measures .007%THD at 2 watts, whereas at 1/1000th watts, THD measures 8.9%! By contrast a Wavac SH833 measures .57%THD at 2 watts and 1.6%THD at 1/1000th watts. The tube Wavac exhibits significantly lower THD at low signal levels by orders of magnitude than the Halcro. I have measured numerous amplifiers, both solid state and tube, which I will provide to you as well as any other information you may want pertaining to this work.

Correlative Listening Tests

...I will now provide a supplementary addition regarding correlative listening tests with a panel of 5 evaluators. Some of the tests were conducted using a blind A/B comparison method, in order to satisfy militant objectivists. The two amplifiers compared were a Wavac SH833 and Halcro DM58. In 10 trials, with listeners blindfolded, every listener on the panel preferred the Wavac by several orders of magnitude, with commentary such as describing the Halcro as sounding: transistory, thin, harsh, dark, closed in spatially, as well as having poor sound floor resolution.

Every listener described the Halcro as being 'unlistenable', while the Wavac enjoyed universal positive accolades. These listening tests correlate exactly with the comparative measurements I outlined.

My research into this characteristic is currently ongoing, and I would enjoy sharing my results with audio enthusiasts, editors, and designers. If this correlation between measurement technique and listening impressions holds up consistently, it could mean a whole new approach to audio engineering could be opened up resulting in significant breakthroughs in design performance. The main idea is to let our ears continue to be the final arbitrator of component performance and allow objective science to enhance our subjective appreciation."

- Steve Keiser

Last edited by a.wayne; 19th April 2012 at 10:40 PM.
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Old 19th April 2012, 10:54 PM   #4494
bcarso is offline bcarso  United States
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Well of course he would have to use signal averaging, and nothing wrong with that per se. But the details of the apparatus should be very interesting. And the spectra of these supposed low-level distortions more interesting still! And what about IM distortion, of far more significance to sound quality than mere harmonic distortion?

We also get into territory here where the presence of some noise may actually enhance low-level detection (so-called stochastic resonance), and as well where some amplifying devices have noise that is signal-modulated. Tubes have been cited as having noise that seems to "float" independently of the signal, and in ways that are somehow easier to separate from the signal.

Brad
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Old 19th April 2012, 11:05 PM   #4495
tvrgeek is offline tvrgeek  United States
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Thanks for S.K. comments. I know of this approach, but I am not sure it is as accurate as it is being presented. This short piece does not say anything about the noise floor. Pulling signals from below the floor is quite a trick. Time averaging beats the heck out of autocorrelation, but it is not magic. ( another technical method brought to you by a large US government agency whom wishes to remain low profile).

Exactly as he states, unprecedented, so I think it requires a bit more explanation. I would love to read more and see where this led.

How old is this posting? I find the links on the WEB to their products dead and their site a search redirect.
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Old 19th April 2012, 11:11 PM   #4496
bcarso is offline bcarso  United States
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Actually his numbers for the DM58 don't square too well with what JA published in Stereophile: even including the noise level (which, for the DM58 isn't really all that low) the 2W traces are rather less than 0.007%. Of course it could be unit-to-unit variation.
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Old 19th April 2012, 11:24 PM   #4497
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by tvrgeek View Post
Thanks for S.K. comments. I know of this approach, but I am not sure it is as accurate as it is being presented. This short piece does not say anything about the noise floor. Pulling signals from below the floor is quite a trick. Time averaging beats the heck out of autocorrelation, but it is not magic. ( another technical method brought to you by a large US government agency whom wishes to remain low profile).

Exactly as he states, unprecedented, so I think it requires a bit more explanation. I would love to read more and see where this led.

How old is this posting? I find the links on the WEB to their products dead and their site a search redirect.
B& K is out of Business , he is with Luminance Audio, send him an email there I guess ...

http://www.youtube.com/watch?v=C7TQJT4HlL0

i sent Steve an email, he may respond ....
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Old 19th April 2012, 11:28 PM   #4498
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Thanks Wayne a lot!
You are not in my ignore list anymore.
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Old 19th April 2012, 11:30 PM   #4499
a.wayne is offline a.wayne  United States
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Errr Ok ... .....
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Old 19th April 2012, 11:33 PM   #4500
SY is offline SY  United States
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My question would be, is noise included in his THD measurement? What do the spectra look like? I can't really make head or tail of his comments since he leaves so much undefined.

Is this copyrighted material? Do you have permission to use it?
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