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  1. #1
    Æresmedlem LMC's Avatar
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    sakset fra March 2012 A.Salvatores sider:
    ( http://www.high-endaudio.com/RECENT.html#Mar )

    MARCH 2012

    AN IMPORTANT BREAKTHROUGH IN...


    MEASURING ULTRA LOW-LEVEL MUSICAL AMPLIFIER SIGNALS

    This may be the most important letter I have ever received from a reader (which is why it is located here and not below). The letter speaks for itself, and is unedited, with my bold. (My "personal comments", plus a sceptical and cautionary perspective from another source, will follow below).

    "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."


    Personal Comments

    The results of these measurements, and listening tests, are not surprising to me. They confirm what I, and many thousands of other audiophiles and music lovers, have heard since the 1960's. I just wish someone had discovered Mr. Keiser's breakthrough method of measurements a long time ago. From my perspective, Steve Keiser may eventually deserve some sort of "Audio Nobel Prize" for his work, at least after it is verified by other objective audio scientists and technicians.

    This new measurement procedure may also be a vindication for me personally. Back in 1999, on this website, I wrote a short article about "The Problems With Measurements", which is concerned with a closely related issue. It is still posted in My Audio Philosophy.

    Further, these new measurements, as important as they may turn out to be, still don't address what musical information is actually "lost" at low signal levels. The added distortion appears to explain the Halcro's (anecdotal) sonic problems of "harshness", but I believe the "leanness" is caused by a loss of harmonics, which are still unmeasurable, as far as I know.


    A Cautionary Viewpoint (From a Surprising Source)

    To gain another perspective, I asked Israel Blume, of Coincident Speaker Technology, to respond to the posted results of Steve Keiser's THD measurement experiments. As a manufacturer of tube amplifiers, and a SET model in particular, Blume's response below was somewhat of a surprise to me. Here it is, with some minor editing and my bold (with my response below):

    "It is common knowledge that currently applied amplifier measurement techniques are not sufficiently refined to correlate to what we hear. The revelation here is that THD measurements are now possible at the micro power level (as low as 1/1000 of a watt), which the auteur of this technique claims has not been previously possible.

    The question now is: Will this new measurement scheme provide greater insight into the subjective sound of the unit being tested? If previous THD testing is any indication, the answer would be "no". This category of measurement has been clearly shown to bear no correlation to the sound quality of an amplifier (with the exception of ridiculously excessive amounts of measured THD).

    In analyzing the utility of the micro power testing, a significant factor to be considered is the power rating of the unit tested and its design goals. All things being equal, an amplifier designed to perform optimally at low power levels, should be more linear and exhibit lower levels of distortion than one designed for high power applications*, with regard to its measurements at the micro power level. The quality of sound produced by the lower powered amp might therefore be superior, if it was not pushed to beyond its available power limits.

    The sensitivity of the speaker used, and the ease with which the speaker can be driven, would be of enormous significance in comparing the sound quality of these 2 amplifiers. In another system setting, where a difficult to drive speaker is being employed, the reverse subjective results might likely ensue due to the power demands placed upon the low powered amplifier, notwithstanding the large power amplifier's higher levels of THD at the micro power level.

    For the new THD measurements to have validity, a large sampling of every type of amplifier topology and power rating will need to be tested. The subjective analysis will require a speaker system easy enough to drive, that the power delivery of the amplifiers will not be a variable under test. Only the quality of sound should matter. In an extreme example, a SET amplifier, even of the lowest distortion measurable, will not sound right on a 82 db sensitive speaker with an impedance that dips to 1 ohm, while a high current, large power amplifier with much higher levels of micro power THD, will sound superior on the same speaker.

    I would like nothing more than to have a set of measurements available that could accurately predict the sound of an audio component. As a designer, life would become infinitely easier. I further would be thrilled to have said measurements verify what I firmly believe- No amplifiers in existence can compare sonically to the best SET amplifiers when used on easy-to-drive speakers. For now, much more testing will be required before those assertions can be made."

    *Actually, Michael Fremer, and some other mainstream proponents of "1,000 watt amplifiers", have claimed they have absolutely no sonic downsides at low listening levels. (Example- See Fremer's review of the Musical Fidelity Titan amplifiers, in the June 2009 issue of Stereophile, which is still posted on-line on their website.)

    Personal Notes- This contrarian response from Blume is highly ironic, since he should be extremely thrilled at these results. However, I believe these results, even if still preliminary, are more important than Blume describes. The discovery that an amplifier so highly touted, the Halcro, has much higher measurable distortion than their own specs and reputation, at volume levels which are definitely audible, is an important breakthrough in my opinion.

    Just as important to me, a completely different technology (Wavac/Tube/SET), considered "obsolete" by so many "audio experts", ends up having much better measurements in this very same area. The blind listening tests, while not surprising to me, are also important, as well as the actual sonic descriptions of the two models.

    In the final analysis, I agree with Blume that many more experiments are in order, which I will post as they are received, no matter what they are. This may be only the beginning, but the amplifiers chosen, and the results so far, couldn't be more edifying. Let's hope that future results are equally surprising and revelatory
    solderslinger og raskere enn sin egen skygge

  2. #2
    Oblivion
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    Måle metoden er gode nyheter!

    Men resultatene var jeg klar over fordi dette har jeg både simulert og hørt i praksis.
    Jeg bruker JFET og ikke rør fordi de "posititive" egenskapene er felles for begge,
    men med JFET får en ytterligere noen fordeler som rør ikke har.


  3. #3
    Rubinmedlem Sluket's Avatar
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    At $ 350.000.00 a shot those Wavac's better sound f%@!!,,%g good, or else....

    Forøvrig morsomt at målegutta faktisk kommer inn på dette med matching, og toskeskapen som ligger i 1000 Watt /88 dB.

    Sikkert lært av de tre musketerer her...

    Nå er begeret nådd!



  4. #4
    Moderator bambadoo's Avatar
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    Interesting.
    I don't believe in system matching. If something is good, it's good. If it only sounds good under certain conditions, it is not good - it is incorrect. - Charles Hansen

  5. #5
    Æresmedlem LMC's Avatar
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    sikker på at dette også gjelder for røramper der prisen har 2-3 nuller mindre!
    mvh
    Leif
    solderslinger og raskere enn sin egen skygge

  6. #6
    Rubinmedlem Sluket's Avatar
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    Ja, det var nok nuller å gå på der... Tror jeg ville prøvd standard 833 og en PS Audio P600 først... mulig besparelse på $ 270.000 kjøper jo mye annen morro...

    Er det noen her som har sett noen tabell over typiske distorsjonsdata på vanlig brukte (i lydsammenheng) rør? Om et rør har 2% forvrengningskomponenter ved full utstyring er jo rimelig uinteressant dersom man lunker rundt på 5-10% av effekten.

    Nå er begeret nådd!



  7. #7
    Æresmedlem HCS's Avatar
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    Noe å tenke på for flere her...
    “Music expresses that which cannot be put into words and that which cannot remain silent”

  8. #8
    Hifi Freak
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    1% ved 1mW er ikke mer enn -50dB. Ref 1W.

  9. #9
    Hifi Freak OMF's Avatar
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    Vel....kjenner jeg blir litt skeptisk.

    Han har muligens målt noe interessant.....men når man måler på såpass små signaler så vil jo en klasse A/B forsterker (som jeg antar at Halcro er) i grunn jobbe ene og alene i crossoverområdet, mens en klasse A forsterker som Wavac er vil jobbe i det lineære området. Jeg tror nok mye av den målemessige forskjellen ligger der og ikke i noe mystisk og hemmelig med rørforstekrere. Dette er ok resulateter som man kan simulerer dersom man ønsker det.

    Men spesiellt vitenskapelig blir det jo ikke...disse forsterkerene måler jo svært ulikt - både på dempingsfaktor, frekvensrespons, forvrengingskarakteristikk og alt annet det er interessant å se på. At de foretrekkes i en blind lyttetest sier heller ikke all verden annet en at en lyttegruppe nettop foretrekker denne lyden. Men å overse alle de andre gedigne forskjellene mellom disse ampene for deretter å proklamere at årsaken ligger i forvrengningskarateristikk ved 1/1000 W -er vel mildt sagt ambisiøst!

    Da hadde vært interessant dersom man hadde sammenlignet med feks en nyere PASS konstruksjon i klasse A.

    Mvh
    OMF

  10. #10
    Hifi Freak
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    Sitat Sitat fra OMF
    Vel....kjenner jeg blir litt skeptisk.

    Han har muligens målt noe interessant.....men når man måler på såpass små signaler så vil jo en klasse A/B forsterker (som jeg antar at Halcro er) i grunn jobbe ene og alene i crossoverområdet,
    Nå blander du med klasse B. Hele poenget med A/B er at man har litt hvilestrøm, så ikke man får crossover ved lave nivåer.

  11. #11
    Oblivion
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    Sitat Sitat fra OMF
    Vel....kjenner jeg blir litt skeptisk.

    Jeg tror nok mye av den målemessige forskjellen ligger der og ikke i noe mystisk og hemmelig med rørforstekrere. Dette er ok resulateter som man kan simulerer dersom man ønsker det.
    For 20 - 25 år siden drev jeg og forsket på dette og simulerte en mengde forsterker teknologier og komponent teknologier...
    Ikke mye mystisk eller hemmelig med dette.

  12. #12
    Hifi Freak OMF's Avatar
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    Sitat Sitat fra Hi-Fi akustikk
    Sitat Sitat fra OMF
    Vel....kjenner jeg blir litt skeptisk.

    Han har muligens målt noe interessant.....men når man måler på såpass små signaler så vil jo en klasse A/B forsterker (som jeg antar at Halcro er) i grunn jobbe ene og alene i crossoverområdet,
    Nå blander du med klasse B. Hele poenget med A/B er at man har litt hvilestrøm, så ikke man får crossover ved lave nivåer.
    Vel - man jobber i et ulineært området! Dette er med andre ord å bruke mikroskop på en kjent forvrengning.
    Hele poenget med klasse A er jo å løfte arbeidspunktet slik at også maks negativt ligger i lineært arbeidsområdet!

    Et annet poeng er jo også hvordan dette utviller seg oppover.
    Et eller annet sted snur vinden - altså at Halcro er best igjen...er dette på 1/10 Watt eller 1/100 Watt.....det blir litt søkt å fokusere på måling ved 1/1000 Watt!


    Mvh
    OMF

  13. #13
    Hifi Freak
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    Sitat Sitat fra OMF
    Sitat Sitat fra Hi-Fi akustikk
    Sitat Sitat fra OMF
    Vel....kjenner jeg blir litt skeptisk.

    Han har muligens målt noe interessant.....men når man måler på såpass små signaler så vil jo en klasse A/B forsterker (som jeg antar at Halcro er) i grunn jobbe ene og alene i crossoverområdet,
    Nå blander du med klasse B. Hele poenget med A/B er at man har litt hvilestrøm, så ikke man får crossover ved lave nivåer.
    1: Vel - man jobber i et ulineært området! Dette er med andre ord å bruke mikroskop på en kjent forvrengning.
    Hele poenget med klasse A er jo å løfte arbeidspunktet slik at også maks negativt ligger i lineært arbeidsområdet!

    2: Et annet poeng er jo også hvordan dette utviller seg oppover.
    Et eller annet sted snur vinden - altså at Halcro er best igjen...er dette på 1/10 Watt eller 1/100 Watt.....det blir litt søkt å fokusere på måling ved 1/1000 Watt!


    Mvh
    OMF
    1: Nei, ikke på en klasse A/B. Klasse A/B gir ikke crossover/ulinearitet ved lave nivåer. Klasse A gir ikke tilsvarende på noen nivåer.

    2: Det er ganske så relevant. Selv bruker jeg 40/1000W (peak) ved full guffe (så mye jeg orker i rommet mitt).

  14. #14
    Hifi Freak Rune S's Avatar
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    Veldig spennende Leif!




  15. #15
    Hifi Freak Cobra2's Avatar
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    Ser ingenting nytt i artikkelen...noen prøver stadig å finne en "min måling sier alt", og påstanden
    blir like raskt plukket i småbiter...

    Arne K
    Of all the things I've lost, I miss my mind the most.
    For sale:
    http://www.hifisentralen.no/forumet/...ser&userid=701

  16. #16
    Overivrig entusiast BerntJ's Avatar
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    http://www.stereophile.com/content/w...r-measurements

    "So, that's that for the Wavac SH-833. I can't explain why Michael found its sound so seductive; all I can do is point to the measurable problems or audible idiosyncrasies that must be listened through to hear what it does right. "

    http://www.stereophile.com/content/h...rements-part-2

    "The Halcro dm58 is a paradigm-destroying component that could well justify the creation of a "Class A+" amplifier category in "Recommended Components." It is really that good. I don't entirely know or understand why that is so, and Bruce Candy is giving no secrets away, but the unassailable proof was in the hearing. Whatever its flaws may be, their discovery may have to wait until someone, somewhere, has developed an even better amplifier. "

    Jaja...Bernt

  17. #17
    Bransjeaktør Bjørn ("Orso")'s Avatar
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    LTS var ikke så begeistret over Halcro i sin før og etter test. Den ble funnet noe farget, altså med klar hørbar forvrengning.

    AB testen forteller ikke mye. En ABX test med positivt resultat mellom produkter hvor den ene måler bedre i et område som man ikke regner som hørbart ville vært noe helt annet.

    Er heller ikke sikker på om dette egentlig er noe nytt bortsett fra selve målemetoden. Har forstått det slik at flere som har studert litt dette med signalkvalitet hevder at vanlig målemetoder ikke vil vise alt som er hørbart.

    Her er forøvrig noen interessante tanker fra Earl Geddes:

    In my mind its not tubes versus transitors, its crossover versus non. Virtually all transitor amps are AB and thats a recipe for disaster at low level zero crossings which is exactly where things are the most audible.
    "
    Someone else
    "Are you referring to crossover distortion? And if so, would you say that high sensitivity speakers make such things more audible? Maybe could be some form of harshness?"

    Geddes
    "Yes, crossover distortion, and yes I do believe that high efficiency speakers will accentuate this problem. You are very perceptive. I believe that what audiophiles call "lack of detail" could well be related to this since "detail" means low level signals and the lower the level of the signal the more it is affected by crossover distortion. In my studies of the audibility of distortion crossover distortion was, by far, the most audible and insidious. So much so that it is all I look for in an amp. Curiuosly, the way amps are measured and rated this problem won't show up.
    "

    Someone else
    "How would one measure crossover distortion? Great thread!, BTW. "

    Geddes
    "If you look at the spectrun of a 1kHz tone as the signal level is reduced the harmonics should fall with level or stay the same. If they grow, or even worse, the number of orders increases (which is very common) as the signal is reduced then there is crossover distortion and you should throw the amp away. You can't look at THD VS level, because at low signal levels all you are measureing is noise. In a good amp, like I have, the harmonics of the signal should disappear into the noise floor as the signal level is reduced. There are actually ways to measure this using a sychonous signal that will measure below the amps noise floor. This is very revealing.
    "

    Someone else
    "Interesting. The only way I knew to get around the problem of crossover distortion and high efficiency speakers was to use a class A amp. "


    Geddes
    "Not at all, there are very good solid state class AB amps out there. The best one that I have tested is my Pioneer receiver, which uses chip amps. Chip amps are inherently better off in class AB because the component matching is ideal (same substrate). My Pioneer has only a second harmonic all the way down into the noise floor, no higher orders at all. NOT SO for most receivers. And you are correct, the spec sheets and advertising are totally meaningless when it comes to audible quality. Unless you measure it yourself you have no way of knowing if its any good.
    "

    Someone else

    "So let me get this straight. You have a Pioneer receiver, using chips instead of discrete components, running in class AB, and only cost a few hundred dollars. But has no crossover distortion, and has no odd order harmonics? Sorry, I don't believe that.

    Is the volume control analog or digital? Since this is the best you tested, I am curious how many did you test?

    I remember in a tread not too long ago, you said
    "electronics don't matter that much. They are at a point where they can't get much better. Put most of your focus on the speakes"
    But in this thread you seem to be saying that the electronics do matter. "

    Geddes
    "You can believe it or not, but its true. I tested about five amps that I had and the Pioneer was the best.

    People always take my statements out of context. Once one has good electronics - and clearly price and "personal perception" don't correlate with good - then the only thing that matters is the speaker and the room (source material being a given). I have never said that any piece of junk electronics is fine. Only that very inexpensive and readily available electronics place the electronics into the "insiginificant errors" category.

    I know that this is not a popular position and it's not one that I have always held, but I have studied this problem intensely and this is my conclusion. It is, by the way, the same one as held by Flyod Toole and Lauri Fincham and a whole host of other well know audio researchers. It's amp designers and marketers who seem to hold contrary beliefs. "
    Representerer lydogakustikk.no og vera-audio.com

  18. #18
    Bransjeaktør Bjørn ("Orso")'s Avatar
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    Jeg viste linken til Earl Geddes og det var slik som jeg antok. Dette er ikke noe nytt. Svaret fra Geddes:
    I had done and posted this exact same technique and results many years ago. I would have informed the poster of this fact except that it wasn't clear how one sends him a letter. (Maybe he is not too anxious to get letters if he plagerizes his work!?)

    Like him, I believe that this is the key to why amps sound different. I found significant differences in amps with this test, amps which appeared to measure the same under standard tests.
    Representerer lydogakustikk.no og vera-audio.com

  19. #19
    Hifi Freak Sleiven's Avatar
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    Set at det henvises til betydelig forvrengning ved millinivåer. Hvor mange er det som lytter ved 1 mWatt?. dvs 60dB under 1 W ?dvs et nivå på 28db mot et vanlig lyttenivå på 88dB på en meter avstand.
    Ser ikke hvordan målinger på så lavt nivå kan være relevante. Det blir som å sykmelde seg ved å definere feber basert på en temperatur måling på 37.00000001 C.

    sleiven
    Siste redigert av Sleiven; 06.05.2012 kl. 13:00.
    &quot;Not everything that can be counted counts, and not everything that counts can be counted&quot; <br />-ALBERT EINSTEIN

  20. #20
    Hifi Freak
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    Sitat Sitat fra Sleiven Se Innlegg
    Set at det henvises til betydelig forvrengning ved millinivåer. Hvor mange er det som lytter ved 1 mWatt?. dvs 60dB under 1 W ?dvs et nivå på 28db mot et vanlig lyttenivå på 88dB på en meter avstand.
    Ser ikke hvordan målinger på så lavt nivå kan være relevante. Det blir som å sykmelde seg ved å definere feber basert på en temperatur måling på 37.00000001 C.

    sleiven
    1mW er bare 30dB ned fra 1W

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