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Thread: "What The Specs Don’t Tell You… And Why"

  1. #21
    Hi All,

    I hope you don't mind me reopening this thread but I just found it. I am the author of the RMAF talk and I am humbled by the amount of discussion this has generated. There are some very valid comments here. I apologize that my talk didn't offer any definitive conclusions. My goal for this talk is to get people subjectivists and objectivists to hold respectful dialog. There is only so much that I can accomplish in one hour and keep the topic somewhat engaging at the same time.

    I am a governor of the AES and I hear a lot of mockery of the audiophile community among the scientific community. I think this is because many hi-fi vendors have hypothesized why their gear sounds better and have vociferously claimed these hypothesis to be fact without establishing any scientific proof. There is a big difference between hypothesis and fact. However, it is equally wrong of the scientific community to outright dismiss one's observations without providing equal scientific proof that those differences don't exist. Both sides need to work together and admit that there are still things we don't yet understand about the recording and playback of audio sources. Having given versions of this paper to many AES members, I know I have raised considerable awareness to the deficiencies in commonly reported specs.

    IMHO, one of the biggest problems we have is differentiating between correlation and causality. I can say that water causes cancer. All persons that die of cancer have ingested water. And, if we deny water, those patients won't die of cancer. They'll die of dehydration. But look how well cancer deaths correlates to water ingestion. This extreme example shows that we can have a high degree of correlation that has no relevance on causality. The water didn't cause the cancer. History is filled with examples of correlation being confused with causality.

    To me, it is perfectly acceptable to say that something works but the reason why remains a mystery. It is also perfectly acceptable to propose a hypothesis on why something works. In fact, I believe when something is stated as merely a hypothesis, it invites further research. We can certainly benefit from more research. Once research confirms causality, we can then work to quantify differences between products.

    Please feel free to ask questions. I will try to check back and answer when I can.
    Last edited by AP Jonathan; 04-12-2016 at 12:53 AM.

  2. #22
    Member Sponsor Addicted to Best! dallasjustice's Avatar
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    Thanks for posting here Jonathan. I really enjoyed your presentation. I hope you do it again. I'll make sure Amir doesn't get ahold of the the mic next time.

    I think there's flawed think in both camps. For example, measuring audio electronics is important but the electronics' contribution to what the listener hears is very small when compared to the loudspeaker. But you often see folks make the logical error called post hoc ergo propter hoc. IOW, just because something happens before something else in a sequence, that must be the thing causing the event. Although electronics measurement is valuable, IMO, it's overrated.

    Michael.
    Last edited by dallasjustice; 04-11-2016 at 05:01 AM.
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  3. #23
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    Quote Originally Posted by dallasjustice View Post
    That's exactly why I thought, at the time, (and still do) that this presentation can help bridge the gap between the two camps. It certainly opened my eyes to how useless some specs really are and how easy it is for manufacturers to manipulate specs in their favor. In addition, it's easier for me to understand why I can still really enjoy listening to systems which don't sport the best specs. In particular, the important difference between cross-over distortion and clipping is very enlightening. It's clear to me there's still much to be learned about distortion. This means that those who claim to hear distortions which may not be readily apparent from basic testing should NOT be dismissed.

    Having said all of that, I still believe that ALL real distortion phenomena can be measured. It's just a question of finding the proper measurement. That's the disconnect between myself and some others. For me, there's really no point in talking to someone who says they can hear a distortion but refuses to accept that what they are hearing can be measured. I hear what they are saying, but I won't ever understand them.
    Revisited this thread and find myself in complete agreement with you . Especially the second paragraph.

    and AP Jonathan

    Thanks for an an enlightening post. Would like to see post more.
    Frantz
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  4. #24
    Quote Originally Posted by dallasjustice View Post
    Thanks for posting here Jonathan. I really enjoyed your presentation. I hope you do it again. I'll make sure Amir doesn't get ahold of the the mic next time.

    I think there's flawed think in both camps. For example, measuring audio electronics is important but the electronics' contribution to what the listener hears is very small when compared to the loudspeaker. But you often see folks make the logical error called post hoc ergo propter hoc. IOW, just because something happens before something else in a sequence, that must be the thing causing the event. Although electronics measurement is valuable, IMO, it's overrated.

    Michael.
    Hi Michael, I appreciate that you have used the word "overrated" rather than "irrelevant". For experiments to be scientifically valid, they must be repeatable. Repeatability can be difficult to establish in the real world. We measure speakers in anechoic chambers and measure gear with sine waves because these approaches make results very repeatable. Unfortunately, the results are also less representative of the real world.

    My talk focused on amplifier distortion. I never mentioned in the talk that all measurements were made into purely resistive loads. Real speakers are anything but purely resistive. I don't think the world will ever agree on a "standard" speaker load for testing amps. However, there are companies like AudioGraph that make load boxes that can test over a wide range of loads. These load boxes can be more expensive than the audio analyzers they are used with. In other words, we have the technology and know-how to do more meaningful load testing but price is currently an obstacle to widespread adoption.

    Humanity's collective scientific knowledge 100 years ago pales to the knowledge we have today. Things that were impossible then are now ho-hum occurrences. We also know that our rate of new discovery is constantly increasing as well. This leads me to believe that our problems with life-like recording and playback experiences will eventually be mastered. I just can't say when.
    Last edited by AP Jonathan; 04-12-2016 at 12:53 AM.

  5. #25
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    Very good posts, AP
    I like what you said about test signals for measurements being those that are repeatable & as a result less like the dynamic, signals that the device is expected to handle when in operation. Unrealistic loads is another good point & one that applies throughout where measurements are often done on individual devices rather than devices & their system-wide interactions.

    As regards measurements, I believe advances in this area will result from better understanding of psychoacoustics which can be used to interpret data (the measurements) into useful information. This will probably be achieved by the use of algorithms incorporating this psychoacoustic knowledge & post-processing the data into meaningful insights

    An example of such will be found in this 1994 paper from Bob Stuart "NOISE: METHODS FOR ESTIMATING DETECTABILITY AND THRESHOLD."
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  6. #26
    Hi,

    Quote Originally Posted by jkeny View Post
    As regards measurements, I believe advances in this area will result from better understanding of psychoacoustics which can be used to interpret data (the measurements) into useful information. This will probably be achieved by the use of algorithms incorporating this psychoacoustic knowledge & post-processing the data into meaningful insights
    In the area of room acoustics psychoacoustic data which can be used to correlate measurements to what we hear do exist, yet what users and acousticians do is measure a simple in-room response and base any judgement and advice on that simple measurement of absolute sound pressure level, without any consideration whatsoever of these psychoacoustic data: equal-loudness contours and perceived loudness, binaural de-coloration thresholds, direction depending head-related-transfer function/in-ear frequency response, none of this is taken into account. They basically completely ignore the fact that human hearing has a radically different way of processing data than a measurement microphone.

    Klaus
    Speakers: Klein + Hummel O500C, Electronics: Funk MTX preamp, Rane PS1 phonostage, Analog: Michell Gyrodec, SME 309, Shure V15VxMR, Digital: Tascam CD-RW4U, Tascam MD-801R

  7. #27
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    Quote Originally Posted by KlausR. View Post
    Hi,



    In the area of room acoustics psychoacoustic data which can be used to correlate measurements to what we hear do exist, yet what users and acousticians do is measure a simple in-room response and base any judgement and advice on that simple measurement of absolute sound pressure level, without any consideration whatsoever of these psychoacoustic data: equal-loudness contours and perceived loudness, binaural de-coloration thresholds, direction depending head-related-transfer function/in-ear frequency response, none of this is taken into account. They basically completely ignore the fact that human hearing has a radically different way of processing data than a measurement microphone.

    Klaus
    Yes, Klaus, maybe it's just advances in application & understanding that is needed. Perhaps, we have all the necessary measurements we need but they are just being ignored or applied in uninformed ways. But I'm also of the opinion that we have a lot to learn about psychoacoustics & the area of Auditory Stream Analysis (ASA) or how we interpret & make sense of the auditory world. The further learnings in this area can only benefit this hobby of audio illusion production (I have decided to stop calling it audio reproduction)

    Have you got any examples of room acoustics & psychoacoustic data to illustrate your point?
    Last edited by jkeny; 04-15-2016 at 07:02 AM.
    Manufacturer digital products Ciunas.biz
    "The greatest obstacle to discovery is not ignorance – it is the illusion of knowledge." - Daniel J. Boorstin.
    "measure 'accuracy' where it counts by understanding the psychoacoustic mechanisms of the auditory illusion of HiFi" - me

  8. #28
    Quote Originally Posted by KlausR. View Post
    Hi,



    In the area of room acoustics psychoacoustic data which can be used to correlate measurements to what we hear do exist, yet what users and acousticians do is measure a simple in-room response and base any judgement and advice on that simple measurement of absolute sound pressure level, without any consideration whatsoever of these psychoacoustic data: equal-loudness contours and perceived loudness, binaural de-coloration thresholds, direction depending head-related-transfer function/in-ear frequency response, none of this is taken into account. They basically completely ignore the fact that human hearing has a radically different way of processing data than a measurement microphone.

    Klaus
    I agree that mikes do not hear like we humans do. But, there is some recognition of that in the typical downward sloping with increasing frequency target curves used by most DSP Room EQ systems.

    Also, varying equal loudness contours with volume level have been built into Audyssey's Dynamic EQ feature for some time, not that I am a fan of Audyssey, which I formerly used myself. But, with that exception, it is true that most EQ tools do not adjust frequency response for different volume levels. All audio systems have been doing that for decades, ever since the old "dumb" and useless Loudness Compensation switch, which was a ridiculous oversimplification, was eliminated from preamps and receivers decades ago. Good riddance!

    Head transfer functions and in ear response are quite variable and specific to one individual. So, it would not be a good idea to EQ or acoustically treat an entire room for one person's particular response for that and other good reasons. With headphones, yes. See the Smyth Realizer 8 headphone system which does precisely that.

    I think you are oversimplifying the issue and what acousticians and EQ tools actually do measure, which is beyond just frequency response. But, frequency and time domain response are the biggest factors in the distortions that listening rooms create, unless there is reliable evidence to the contrary, which there is not. Correcting just for those is a huge improvement, as you can demonstrate for yourself by trying one of numerous DSP EQ tools. Dirac, for example, measures and corrects both the frequency and time domains. The tools may, like all things, be imperfect, but you do not want to talk yourself into dismissing them as a result: the perfect is the enemy of the good! Also, with Dirac, one can if one wishes create multiple target curves, easily selectable during playback for different volume levels or your own specific, preferred system voicing.

    And, DSP Room Correction is still a very young technology. It has come a long way in the past decade, and it will likely further improve as computational speeds and capacities further improve.

  9. #29
    Duplicate post. Sorry.
    Last edited by Fitzcaraldo215; 04-15-2016 at 09:38 AM. Reason: Delete Duplicate

  10. #30
    Quote Originally Posted by jkeny View Post
    Yes, Klaus, maybe it's just advances in application & understanding that is needed. Perhaps, we have all the necessary measurements we need but they are just being ignored or applied in uninformed ways.
    I don't think we have all the necessary psychoacoustic data in terms of measurements correlated to perception, but the ones which are available today could be used. What I find rather striking is that the very center of this whole room acoustic exercise, i.e. the listener, is not considered at all!

    Have you got any examples of room acoustics & psychoacoustic data to illustrate your point?
    As a start, the equal-loudness contours: a 10 dB peak at frequency X and a 5 dB dip at frequency Y could be perceived as being equally loud. Of course, those curves are averaged so may not apply to the individual listener. Another road to explore may be the works of Toole on resonances (JAES 1988, p.122) and Bücklein on the audibility of frequeny response irregularities (JAES 1981, p.126), can’t remember if they have determined thresholds.

    First reflections: there are many data on perception thresholds, but not for the scenario 2- (or multi-) channel with music as signal. The difficulty here is that human hearing is directional (different in-ear frequency responses for different directions, see Shaw, JASA 1965, p. 465), while a mike is not. Further, a late first reflection will be perceived as an echo while for the mike it makes no difference. Despite all that people measure then go and treat their reflections, most likely with absorbers which don’t absorb but only modify the spectrum (see https://www.audioholics.com/room-aco...man-adaptation).

    Binaural de-coloration: in 1995 Salomons wrote her PHD thesis with the goal to correlate measurements to perception thresholds so that measurements in performance spaces would tell you whether or not the sound would be perceived as colored:

    http://www.google.nl/url?sa=t&rct=j&...hhgd4YgQ3Kk5pw



    Klaus
    Speakers: Klein + Hummel O500C, Electronics: Funk MTX preamp, Rane PS1 phonostage, Analog: Michell Gyrodec, SME 309, Shure V15VxMR, Digital: Tascam CD-RW4U, Tascam MD-801R

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