Misleading Measurements

[fas42]

Well, might have to go back to basics here, http://superior.lakeheadschools.ca/scvi_staff/childs/web-SPH3U1/downloadable_content/unit-8-Waves/textpdf8/phys11_8_1.pdf

 

To wit,

 

Quote

•     A    vibration    is    the    cyclical    motion    of    an    object    about    an    equilibrium    point.
•     All    vibrations    need    a    medium    to    transfer    waves.
•     A    mechanical    wave    is    a    transfer    of    energy    through    a    medium    by    particle
vibration. Particle vibration is caused by a disturbance to the medium.
•     A    medium    is    a    material    that    permits    the    transmission    of    energy    due    to
vibrations. A medium can be a solid, a liquid, or a gas.
•     The    particles    of    an    elastic    medium    return    to    their    original    location    after    a
wave passes through

 

Now, last time I checked, air was a gas.

 

Next step, which isn't in that document, is that non-linearity of the medium reacting to the energy exciting it is what creates difference tones; intermodulation.

 

Now, it's well documented in plenty of literature, that air is linear in its behaviour, unless extreme pressures are involved.

 

Therefore, ...

[fas42]

33 minutes ago, bluesman said:

So if nonlinearity causes IM and you agree that air is linear in its behavior, why do you think that it’s the “source” of IM products?

 

I don't. I was under the impression you did. The energy in the difference frequency has to come from somewhere, and if it's not generated by non-linearity of the medium carrying the sound vibrations, air in this case, then it has to come from some other element in the room. The most likely suspect is some part of the musical instrument, or a nearby object. Either way, what the microphone has captured is a correct representation of the energy spectrum that was created when the strings were plucked, and provided the speaker that then reproduces that capture has minimal IM, then there will be no "doubling up".

[fas42]

12 minutes ago, bluesman said:

You’re assuming that energy is added and I’m not.  The interactions of the compressions and rarefactions in the two waves generate the IM tones, but the total energy in the combined spectrum is no greater than the cumulative energy of the two source tones. The energy to produce IM tones is drawn from the energy in their source as the moving molecules carrying the source tones push and pull other air into the IM products.

 

The microphone is registering energy of the difference tone - otherwise there would be zero level shown on the spectrum, for that frequency. Where is that energy coming from? The air itself, or the instrument or some other object transmitting the energy, as a vibration, through the air, which is acting as the medium?

[fas42]

There's another one,

 

 

[fas42]

9 hours ago, bluesman said:

It’s transferred from the moving molecules of the fundamental waves to the molecules pushed and pulled into the IM products.  The overall energy is the same amount that was transferred to the air molecules by the string or reed or speaker cone, but now it’s distributed among the expanded spectrum.  So the energy in each fundamental has been reduced by the amount transferred to the intermodulation products.

 

Yes, but we are still arguing about where that transfer of energy moved from the fundamental to the intermodulation products. Did it occur in the air, or did it occur in some object which is not the the air?

 

Note, the air immediately adjacent to the instrument is still air, any IM here is from the body parts of the instrument that the air contacts.

[fas42]

Fair point  ...

[fas42]

All that really matters in this whole conversation is whether there is some mysterious, "third force", that adds content to what one hears when listening to a musical instrument - or not. I say, the instrument, and possibly objects which are not air around it are the sole contributors - which means that a decent microphone will pick up purely what matters, which is the sound generated by the playing of the instrument, in the particular environment. Replay of the capture, to an adequate accuracy, will not be additive - because it can't be ...

 

I see @bluesman as having an agenda, to ascribe the veiling of conventional playback to something which can't be dealt with - IME this is completely incorrect; suitably '"debugged" reproduction doesn't have veiling issues - the problem simply evaporates, just like a morning mist 😉.

[fas42]

2 hours ago, Audiophile Neuroscience said:

 

 

IMO we are talking about interference patterns of sound waves in air, specifically beat frequencies. I just don't get why that should be so controversial as a concept

 

It's controversial if you try and connect perceived beat frequencies with lines on a spectrum, from a microphone capture.

[fas42]

 

[fas42]

The snake keeps twisting ...

[fas42]

To prolong the, ahem, medical analogy - what we have is a patient who is feeling somewhat unwell; some medical professionals will be heavily focused on diagnosing a particular cause, out of the many things that possibly are causing a specific symptom, and who will then hit that cause with all the medical knowledge, and pharmaceuticals at their disposal. Someone who is coming from a health coach angle will look at the big picture, and suggest major lifestyle changes, to encourage a better overall sense of wellness - and what is needed are measurements that tell everyone that the patient is going in the right direction, when following that regime, 😉.

[fas42]

I doff my hat to you gents ... I don't have the stamina anymore to indulge in intense wrestling matches like this - interesting to watch from a distance; eventually it will stop, with absolutely zero gained by anyone - and such has been the way of audio for decades now, of course ... 🙂.

[fas42]

The thing is, there are different types of of back and forth - when people throw in lots of technical brouhaha which has zero meaning for the discussion, that's when my head explodes ... 😉.

[fas42]

4 minutes ago, kumakuma said:

 

As did mine.

 

I can't help but feel that he stopped spamming the sh*t out of this site with repetitive posts, he might have the energy to actually contribute in a meaningful way. 

 

You mean, in a way that fits in with your world view, of course ... 😉.

[fas42]

8 hours ago, John Dyson said:

Whether the intermod happens in 'air' or in a 'string', the underlying math is essentially the same as software & electronics emulations of the effects.  I am NOT claiming that precise emulation of the real world is simple, but I don't think that is what we are worrying about.

 

 

What we're worrying about is whether recording the interplay of musical instruments, and then replaying that capture "doubles up" on some, nebulous, thing ...

 

Assuming adequate accuracy of the devices used, the answer is ... that it doesn't.

[fas42]

18 minutes ago, wbh said:

I am still a bit unclear on why certain D-S dacs, as their specs get more and more "unmeasurable",  (esp. AKM), and the sound gets softer and smoother, but NOT more music or exciting. Or the NOS vs. OS crowd. You get the idea.

Hard-core objectivists have very little genetic imagination ... so, eg., they can't IMAGINE a world outside the box of, say, a Univ. Physics textbook publ'd in 2008.... that even basic equations and laws will change or be added to in an edition a few decades from now.

Think of all the "basic" science questions of day -- dark matter, dark energy, the "Hard Problem", etc. -- and then work back to how absurd objective complacency is in audio. 

 

It's actually very simple ... no-one measures how robust audio systems are to resisting the influence of electrical interference, noise factors - these are just thrown into the "good enough to get a sticker meaning that it meets some EMC standard" box, and that's the end of it.

 

Highly "over-engineered" components actually do enough to mitigate these effects - they that shall never be mentioned, 🙂 - and the SQ, works.

 

The refusal of objectivists to take interference mechanisms seriously is a key factor of why so much nonsense exists in the audio world - at a practical level, this has to be dealt with, to get accurate reproduction of what's on a recording, irrespective of whether a rig costs $500, or $500,000 ...

[fas42]

7 hours ago, botrytis said:

 

Not so fast there. Subjectivists also refuse to show ANY data to prove that EMI does cause interference and it is large enough to do so. Right now is all in the urban legend/urban myth realm. Even on this board, there are a variety of threads on this topic without any data other than subjectivist listening results. That can be boiled down to, you wanted it to sound better so it does.

 

Because the interference factors that are crucial are difficult to measure - in terms of the usual quantitative results that people use to assess audio quality. I haven't had any inclination to try and get numbers, because everything I've read has indicated that people who have full access to equipment that should pick up something have had no success with trying to see correlations.

 

Anyone who takes audio even vaguely seriously knows that all sorts of noise inducing mechanisms matter - everyone who tries a power conditioner or filter, or considers separate power runs, or worries about the type of lights in the listening room is dealing with this. The ears tell the story - and that's what matters.

 

Wanting it to sound better? Interference makes it sound like crap - you don't want to keep listening ... solving these issues brings back the enjoyment factor; a relaxed ease to the sound which means you can run at high SPLs for extended periods without fatigue. And this is something that "good numbers" can never replace.

 

What's actually happening is that low level detail in the sound presentation is being corrupted, had had enough noise added to it to make it difficult for the listening mind to interpret the meaning of that detail - this is why the sense of unease with sub-par SQ builds ups, and hinders long term enjoyment of the listening.

 

Quote

Both have to be dealt with. Can one actually measure the interference? If one can, is it large enough to make a difference? If not, how can one ameliorate what one cannot quantify?

 

 

 

The ears tell you. If a sense of irritation with what you are listening to keeps intruding, then you have an issue ... so, indeed it makes a difference. Simple experiments are often enough to identify a cause and effect link - the hard bit is often to work out a fully comprehensive solution, that is 100% robust; workarounds are often a decent alternative

[fas42]

2 hours ago, botrytis said:

Ears can be fooled. The number one hallucination is auditory. Ears are also subject to emotional bias. So, I do not trust 'Golden Ears'.

 

Maybe there is a reason it is hard to measure, it doesn't exist. Playing Devil's advocate here. The underlined part is important. If they can't measure it, maybe it is all in your head.

 

Something to think on.

 

Key word is "maybe" ... ears don't have to be "Golden" - just, 'trained'. A good exercise is to get a recording that is marginal, on one's particular rig, that is, depending upon the phase of the moon, etc, it can sound good - or quite "off". Then, organise some severe form of interference source - an arc welder plugged in to the socket next to those of the audio components, and operating, can be a juicy one, 😁. Now, unless miracles do happen for some audio rigs, one should notice a change in the SQ - that with, and then without interference.  You now have a marker, and can scale back the severity of the test setup 🙂 - this is a way of attuning your hearing to what's going on ... of course, the down side is that from then on you will become aware of this factor in play, 😉.

 

People who have a philosophical need to disbelieve that this can happen will muck up doing the exercise, unfortunately ... it's more important for them to sustain their belief system, than to learn more about what matters, 😜.

[fas42]

Most people are aware of the situation where they can hear some very expensive rig, and know very quickly that they don't want to keep listening to it; and similarly come across a very modest setup, which is a delight to listen to, and where they keep thinking of more music that they want to experience, on it. That's where measurements should come in - but they, mostly, don't.

 

This is the area I work in, and, I don't measure. The flaws in the first system I just mentioned are highly audible, but difficult to detect with instrumentation - but this doesn't matter. Experience and experimentation allow one to track down the cause(s), and then either engineer a solution, or tweak with some workaround - the fact that at no time were any numbers forthcoming is irrelevant, because usually you're not dealing with a shortcoming in some obvious audio parameter, but rather a clear fault with the overall integrity of the playback chain.

[fas42]

16 hours ago, Confused said:

If you have "an expensive rig" that fatigues and a modest rig that is listenable, I would say that 90%+ of the reasons behind this can easily be measured using something like REW.  With the former, the issues are likely to be caused by tonal imbalance, an overly prominent "shouty" mid range, a bass "suck out" or similar.   On top of this, REW can also measure distortions and other issues.

 

Not in my world. The distortions that cause these subjective impressions are caused by interference and lack of integrity issues, and these are mostly, "unmeasurable" - something I learned over 30 years ago ... and nothing has happened since to change my mind. Literally yesterday I was dealing with exactly such a concern - and the same methods, as always, resolved the problem: the new digital speakers need a good dose of mains filtering to "sing", and I was experimenting with simple EMI suppression parts, to improve the performance of that filtering ... but it took 3 rounds of fine tuning precisely how the wiring in the area where they were fitted was organised, before it came properly good. Yes, I gained in suppression - but an offness was now slowly building in the sound - I had lost my 'silky strings'. Twice I thought I had done enough to stabilise the wiring and insulation, and twice I was wrong - only the last round where I literally used a toothpick to improve the mechanical stability finally did the trick ... and now the string tone was back in order 👍.

 

16 hours ago, Confused said:

I have been to many hifi shows where there is some guy with a video camera filming in all the rooms, and others that dish out "best sound in show" awards.  I have no problem with either of these, all good fun.  However, it would be interesting if before the start of the show someone went from room to room, measuring with REW or similar.  (I know this is never going to happen, BTW)  Then when all the subjective views of the visitors are compiled, you could compare this to the measured responses of the systems in the rooms.  I am sure that there would be some kind of correlation between the "listenable" and "fatiguing" systems with the measured results from REW.

 

Bev knew I had a problem - "the cello's not right" ... objectivists would laugh hysterically at the "tiny thing" that did the trick - but everyone who goes the 'burning in' phase with new stuff is dealing with the same behaviour ... I prefer to make it right from the get go, 🙂.

[fas42]

Misleading? ... Just saw the Stereophile review of the NAD M33, and the measurements are pretty ordinary, in the distortion area of things - https://www.stereophile.com/content/nad-masters-series-m33-streaming-integrated-amplifier-measurements. That is, compared to what Purifi is able to show as being the capability of its Class D modules as regards distortion, "when measured the right way", 😉.

 

So, who is right? Both of course ... so, why do measurements matter, 🙂? It might make you feel good, to know that bits of the whole can do brilliant stuff - but in the real world, implementation is everything ... unless extreme attention to detail is part of the deal, all the theoretical, measurable performance counts for nothing - in terms of what reaches your ears, 🙂.

[fas42]

3 hours ago, Confused said:

 

Another point to consider, the Stereophile measurements are of an integrated amplifier, not just an amp module.  So the volume control is included in the measurements via the analogue inputs, and the DAC also for the digital inputs.

 

For me, the Stereophile measured distortion measurements look fine, I would not expect any audible distortions based on the measurements provided.

 

Yes, of course that's how it works - the sound of a rig is always the sound of the worst performing parts of the whole; the ideal for many people is that the playback chain is completely "transparent" - otherwise, you're just seasoning a soup, 😉.

 

But I mention it in the context of measurements "being misleading" - some people will think that some magic occurs, that having an extremely low measuring distortion device in there transfers its specialness to everything else ... well, it may be where the crucial bottleneck that held back the SQ before was, and then you do win - but it's never a guarantee, 🙂.

 

NAD are bringing out a conventional separates power amp, using the Purifi modules; will be interesting whether they can deliver the promised performance there.

[fas42]

To me, the divide is between those who want to be certain that they have a handle on everything; and those that know they don't. People who need to feel that they can have full control over what guarantees "correct" sound will gravitate to the ASR site, because it backs them up in that belief - merely apply the "correct" tools, measuring devices, and out pops perfect SQ - and all is sunny in the world, 🙄.

 

The majority of audio enthusiasts know that the real world doesn't work that way ... full understanding of what needs to be done to ensure the best standard of subjectively satisfying replay just doesn't exist - floundering around until an acceptable standard, for them, is achieved is generally how it's done. Which for the ASR crowd is completely unacceptable.

[fas42]

1 hour ago, pkane2001 said:

 

As I see it, the divide is between those who want to believe and those who want to know. And then, there's also Frank ;)

 

 

Ah, Frank sees two plots of ground on either end of the field; one heavily populated with those who believe and who are not particularly interested in knowing, and the other with a large group who scorn those that believe - in the middle is a largely empty area, where he sits and is very much lacking in company, for those who believe what their ears tell them, and also want to know. Here, the understanding that one has to widen one's thinking, and not dismiss new or different concepts because they don't immediately appeal, is important - such understanding is not popular, and generally gets the thumbs down response, 😜.

[fas42]

52 minutes ago, 992Sam said:

 

why not?  With Covid, and it being a holiday evening, I'm bored and this thread has been entertaining to say the least...    

 

Would be nice to see a true study done between what is measurable in terms of audio quality and what is psychological and subjective....  I also have to wonder if a lot of the 2nd, 4th and odd order harmonics that are masked / amplified by certain setups in power supply, cable shielding, and other EMF/RF factors aren't more easily heard by some than others and thus the endless debate over measurement vs how it sounds?

 

It's really very easy ... if it's trivially obvious when you hear music coming from somewhere, that it's an audio system - then the distortion is audible. When the distortion and misbehaviour that matters is inaudible, then all the qualities that audio people chase will be there in abundance - no-one really knows how to measure one state versus the other; hence the ongoing kerfuffling ....