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Hi DroneB,
I am the person who posted a question about intermodulation and human hearing on Science Desk. You responded to a squawk on a talk page created for me, which I assume is about to disappear from the Wikipedia system, as my question is about to roll off into oblivion as new questions are added. To make this easy, I have copied your response here. I hope that is ok to do. Regards.
- Hi. You may remember that I responded to your question about Hearing at WP:RD/S.
- 1. I hope that you and Nil Einne patch up present disagreements. Nil Einne's concern about correct understanding of whether human evolution continues is undoubtedly genuine and supported by references that he provided [3]. I shall say that neither of you two look well in the unfriendly, unreferenced dispute [4], [5] that followed. Nil Einne was also unhappy [6] with Nimur's response that argued from music history that preference for harmonic sounds is an aesthetic, not an evolutionary, effect. Your singling Nil Einne out for abuse by name, IP user 121.44.191.221 was undoubtedly hurtful and seems poorly considered.
- The outcome of the performance at the Ref. Desk is that Nil Einne considers himself still in dispute with you, and further suspects that you are a ban evader. From his hedged hints refers to these diffs: [7] [8] [9], he may be insinuating that you are or have been Wickwack, who is found here. You have a right to hear whether that is his belief, and if so whether he claims it to be more than coincidence that the banned Wickwack addressed the subject of audio distortion in posts some 5 years ago. Incidentally, it's a respectable subject in Wikipedia.
- 2. I accept your point [10] that levels of IM that seem too low to affect perception of sound direction can still make reproduced sound unpleasant. Looie496 mentions the function of harmonics in perception of single contra multiple sound sources. Certainly our hominid ancestors who depended on sound localization for survival did not enjoy the luxury of relaxed listening to an orchestra on a stereo sound stage, where an audiophile may demand 0.1% IM.
- 3. Thank you for considering my off-topic [11] idea of cancelling IM in old recordings. This idea is based on success that I have seen in cancelling distortion of video in non-linear amplifiers by applying an opposite pre-distortion. You mentioned the complex harmonics of sound, but video is more complex and the method does not involve a harmonic analysis (not that a "warehouse full of supercomputers" could not be assembled if needed). My thinking is that IM-producing non-linearity can be corrected provided that it arises at a single point in the signal chain, and that there are no prolonged resonance frequencies (implying energy storage) or amplitude limiting e.g. fuzz guitar.
- 4. It's relevant to your question that human senses are all functionally non-linear, not least the Auditory system whose frequency and amplitude ranges are better quantified on logarithmic than linear scales. Thus at cellular level harmonic distortion is always present, and always has been in nature! It is a product of evolution that we have perceptual compensations for our own-generated harmonic distortions. This viewpoint, if true, turns your question around. Pure harmonic distortion may be dealt with by a kind of subjective volume control, comparable to the function of the iris in sight that serves to keep the stimulus strength within a small range that can be perceived linearly (comfortably). However we haven't been able to evolve a way to unperceive IM products, hence their special unpleasantness. DroneB (talk) 01:51, 3 August 2018 (UTC)Reply
- RDL is short for Language Reference Desk. DroneB (talk) 01:51, 3 August 2018 (UTC)Reply
Taking your numbered points in order--
1. Nil Einne
We have not patched up. He/she has no way to contact me, and I see no reason to contact him/her, other than the talk page he/she posted to. I'm all for obtaining harmonious relationships, but it is for Nil Einne to make a move - after all he/she started it by posting an insulting response (as in 'your question contains misunderstanding and false assumptions.' Without any explanation (none made at the time I squawked), that's just treating the questioner as an idiot. If you were at school, and you asked in good faith a question of the teacher, and you got that sort of response, how would you feel? None too pleased I reckon. Or you asked your boss a question? Same thing.
The fact that Nil Einne went off on some bizarre rant some posts by someone else, etc, etc, confirms the intent to insult or perhaps troll. It is human nature that guilt cause a negative reaction to protests and insults, whereas with people who were acting in good faith or made a genuine mistake, its either water off a duck's back, or they don't respond at all. I'm not Wickwack. And if anyone else posts about intermodulation of distortion, the chances of them being me or Wickwack are remote. Wikipedia has been running for years. By now I expect you could find someone has posted on every subject imaginable. To assume two posts on the same subject must both be by the same person is silly.
I accept that my further response made answers to my question unlikely, I realized that at the time, but (rightly or wrongly) I thought the likelyhood of getting a useful answer was gone once they started going on about whether or not evolution in humans has stopped. I wish I had not mentioned that evolution had effectively stopped, which for electronically reproduced sound is obvious. It was a matter of trying to salvage the question and hoping someone else would respond.
If my squawk against Nil Einne results in him/her thinking twice before insulting questioners again, then I have done everyone including Nil Einne a favor.
To assume
2. Detectable IM levels too low to affect perception of direction.
Yes.
3. Correction of non-linearities.
For single point distortion, it can and is done in audio too - been done for 50 years or more. For example non-linear companding/expanding. But you asked about restoring old records - in such cases that sources of non-linearity are multiple and its generally not known just what they were.
Do not underestimate the quantity of distortion products produced by intermodulation. As the number of frequencies in the sound source go up, and the order of the non-linearity, the products increase like N-factorial. Each IM product may be at imperceptible level by itself, but there can be so many of them, that the total energy seriously affects the perceived sound.
4. Auto adjustment of human sense sensitivities.
I think you are confusing what is called "automatic gain control" by electronic engineers, which is the same as "recruitment" so called by audiologists, with non-linearity. The iris of the eye is not a non-linearity. Neither is the stapedius muscle in the ear, which is part of our in-built automatic volume control. AM radios have, as well as the manual volume control, and automatic gain control. When you tune form one station to another, they all seem to come in at the same level. Without AGC, and AM radio is intolerable to use, because each station will come in at a level depending on distance, transmitter power, present of power lines, etc etc. This doe not make the sound distorted. Its not a non-linearity, no more than the manual volume control.
Human hearing has the stapedius muscle - it acts under command of the brain, unconsciously, to effectively jam up the eardrum by varying degrees. The auditory nerve acts two-way - the brain sends signals to the middle membrane of the cochlear to alter the effective sensitivity of the hair cells, which convert vibration into nerve signals. A single quiet tone (single frequency) will excite only one, or perhaps two, hair cells - the one that is tuned to that tone. If the tone gets louder, more and more adjacent hair cells respond. The brain can use this to figure out how loud a tone is, and adjust accordingly. None of these mechanisms are non linear - they do not inherently cause harmonics or intermodulation.
Regards, OP. 121.44.39.59 (talk) 03:57, 4 August 2018 (UTC)Reply
- I am happy to continue our discussion here as you suggest. For continuity's sake I take the liberty of replacing your copy of my post so that all the links work. I also inform Nil Einne who is welcome to comment on anything we say. I shall have control here.
- Keeping to the numbered points:
- 1. The history of evolutionary biology is rife with assumptions that are constantly questioned, attacked and defended. I don't think it surprising to be told that an implied assumption that evolutionary theory promises a direct causal explanation for a particular human feature is a faulty assumption. To be fair to you, you no longer insist human evolution stopped at the caveman or stone age, which caused a brief digression at the Ref. desk. You fed the digression [12]. To be fairer to Nil Einne than you seem willing, his post takes you seriously, it provides ample references for what he says, and at no point do I see any insult. Your next post depresses me because you contradict Nil Einne with nothing more meaningful than to associate him with a flat Earther and/or a substance abuser. I won't dictate how you restore harmony with Nil Einne because an honest outreach has to come from you alone, but the rudeness here should be a place to start. If you think my schoolteachers are relevant, I shall say they were paid to tell me whether I understood things rightly or wrongly, not to make me feel comfortable.
- It's impossible and inappropriate for me to arbitrate on the Wickwack accusation. I can understand your feeling of injured innocence and it's obvious that Nil Einne is not feeling happy about the idea. I believe in your natural right to have an accusation made clear or withdrawn (Nil Einne may choose to weigh in here) but I shall close this page if there is more bad faith language such as "went off on..rant..confirms the intent to insult".
- 2. Good.
- 3. I agree that Companding works well but the gain changes are too slow to cause distortion products.
- 4. Thank you for educating me about my smallest muscle Stapedius of which I was unaware. Until now, I supposed that our hearing gain control was entirely neurological. Now I see a likely connection between the psychoacoustic masking that MP3 compression exploits and the mechanical response of the stapedius. To explain: we can hear a machine gun 130 dB ref 10-12W or a whispered word 20 dB ref 10-12W. But we can't hear the whisper immediately after the gun fires because it is masked for a short time by the louder noise. I don't yet know how well the Time constants of the mask decay and stapedius match, and I think we still need a neurological explanation of the pre-masking viz. that we don't hear a whisper immediately before the gun fires.
- I would have to question my assertion that "human senses are all functionally non-linear" if someone could probe the Cochlear nerve and extract high fidelity music.
- Best regards, DroneB (talk) 14:35, 4 August 2018 (UTC)Reply
- Again, your numbered points in your order----
- 1 Squark with Nil Einne.
- Seems to be a case where each of the 3 parties has said what they want to say. So discussion closed unless perhaps Nil Einne responds here.
- 1 Just to clarify: I still think that human evolution has largely stopped. Evolution works via survival of the fittest. That is, only the well adapted get to produce the greatest number of offspring. But in the modern era, humans have learnt to alter their environment so that the unfit survive, either by being propped up by society or by getting their medical conditions fixed. This is not of course sustainable. The global environment will ultimately produce a reckoning, one way or another. This is in no way relevant to my question, as I have stated. Only the fact that human hearing cannot have evolved for electronic reproduction, which has a history going back only ~100 years or so, is relevant.
- 3 Companding
- I mentioned non-linear companding, which is instantaneous. You seem to have confused it with gain companding, which does take (a small) time to respond/operate.
- An example of gain companding is the old Dolby system for use on analog tape decks. This works by the circuit continually monitoring the level of treble, and boosting it proportionally when the level is low. During playback, the level of treble is again continually monitored by the electronics, and if the level is high, its left untouched, but if the level is a little bit low, it cranks the volume down further, so that the original treble level is restored. And the noise and distortion inherent in analog tapes is reduced along with it.
- The disadvantage of Dolbly is that it takes a small fraction of a second for the circuit to respond to changes in level. If a low level treble signal is immediately followed by a loud treble sound, the system can be driven into overload until the thing responds. Fortunately the ear is not very sensitive to single occurrences of momentary distortion. But apart from this occasional momentary distortion, Dolby is a linear system and does not normally generate harmonic or intermod distortion.
- Dolby's advantage is that, because it is a linear system, its no critical in its adjustment. Any slight mismatch between recording and playback just slightly alters the music's volume and dynamic range.
- An example of non-linear companding is a system used for long distance transmission (eg radio network programme distribution), before the advent of digital methods. In this process, the audio signal is processed by a circuit that contuinually and instantaneously calculates the logarithm of the input. This emphasizes slight waveform changes and flattens the peaks. This is considerable non-linear distortion and if you listen to it, it's really horrible - huge amounts of harmonic and intermod distortion. At the receiving end, the circuit calculates the exponent of the incoming signal. This is also a distorting process, but it exactly reverses the distortion done at the sending end.
- The disadvantage of non-linear companding is that adjustment is critical. Any mismatch between sending and receiving circuits leaves distortion.
- It's advantage is that works instantaneously, so momentary overloads on loud sounds cannot occur.
- 4. Hearing auto volume control
- I gave you a simplified explanation. It's a complex and very interesting subject. Many misconceptions abound, even in professional circles, both medical and electronic. If you want to follow up, the Philips company sponsored a research institute in Holland, which has since the early 1950's done incredibly good work. Unfortunately, this work is little known in English-speaking countries. I suspect that this is because their output is in the Dutch and German languages, and because some of their findings are in complete disagreement with long-standing views of English speaking experts. For example, you still find textbooks reckon the ear pinna (the curiously shaped external cartilage) is critical in direction sensing. The Dutch institute proved conclusively that it isn't. It's purpose is probably nothing much more than to assist humans and their ape cousins recognize each other. For direction sensing, the pointy ears on some breeds of dog is quite superior.
- The classic text of how hearing performs is --Psychoacoustics: Facts and Models-- by Eberhard Zwicker. This is available in English and has gone through numerous revisions over the decades, including by his grad student after Zwicker died of old age. The book is fascinating because it has an extraordinary amount of tabulated and graphical data on just what our ears can and cannot do. For example, he has shown that the human ear's own added distortion is of the order of 0.1% for important frequencies at reasonable levels, but as much as 4% for deep bass. That is all way greater than what modern electronic amplification and digital recording routinely achieves.
The stapedius muscle is very fast. It actually can go from full tension to completely relaxed and back again in milliseconds. But if you are right next to a large gun, 100% stapedius tension isn't enough. Sound vibration reaches the inner ear at a level the hair cells can't cope with, so they "lock up" for a while.
The stapedius muscle is very smart - or at least the brain is. Ever noticed that if you are hammering something, it doesn't seem uncomfortably loud, but someone else nearby complains? That's your stapedius muscle working. Your brain knows exactly when the hammer is going to strike, but your friend's brain doesn't. Ever wondered why when you are chatting to a friend, whose head might be a few feet from yours, it seems like you are both talking at the same level, but if you move a few inches from a microphone, it makes a big difference. That's because the mike doesn't have a stapedius muscle. You do, and yours tension up syllable by syllable when you talk, so you don't deafen yourself, even though your mouth is only 3 inches from your ears.
- PS: Don't be too distressed if I don't come back here again. I get to this page each time by first going to Wikipedia home page, clicking on Reference Desk, choosing Science Desk, going to my question, then clicking on <talk> after your name. I'm not sure I can find my way here when the question gets rolled off and deleted. I'll probably figure it out, but I might not.
- I've posted questions on Wikipedia Reference Desk probably about 4 or 5 times over the years. A couple of questions attracted very helpful and useful answers, but my experience of it generally is not good. Too many trolls. Too many who just like to sound off instead of answering the question. Other forums, eg diyAudio are much better, but they are subject specific. I live in hope that Wikipedia will improve.
- Regards, 121.44.164.157 (talk) 16:58, 4 August 2018 (UTC)Reply
- 1. I don't see how you can claim that human evolution, specifically change in heritable traits over generations, has stopped when this example shows the ongoing action of natural selection through disease in a mid-20th century human population. Complaining that we do wrong to help "the unfit" who? survive sounds like Eugenics rhetoric.
- 2. -
- 3. You are right that I assumed you meant gain companding. Thank you for good explanations of Dolby and of an analog non-linear instantaneous companding that I didn't know existed. I know of A-law and μ-law companders for digital telephony. These companders can of course be overdriven by exceptional signals.
- 4. Thank you for referencing an important textbook which I find is readily available. I understand that the stapedius muscles can prepare for loud sounds that my brain anticipates. That does not explain the pre-masking before a sound that cannot be anticipated.
- It should not be difficult to come to my Wikipedia page by entering User:DroneB . You will be specially welcome and get a page of your own if you choose to open an account and be known as more than just an IP number.
- Footnote: Your obvious expertise and closeness to Dutch Philips makes me wonder whether we might share an interest in PSQM.
- Best regards, DroneB (talk) 21:44, 4 August 2018 (UTC)Reply
- I got here easy by clicking on history.
- 1. When I said human evolution has essentially stopped, I always included the word --essentially-- or some similar word. I might just as well say that humans are essentially about 1.5 to 2 m in height. That's true, but you do find outliers outside this range.
- The existence of a small (by a world scale) of a population subset who have partly adapted to prevalent malaria because they did not have access to effective medical care does not alter the big picture. My father had malaria, as did most of his generation, who served in World War 2. However, like Australians generally, he got excellent hospital care, recovered 100% regardless of his presumably typical German genetics, and went on to produce me. Just like those other Australians who got malaria. Clearly, for Australian soldiers, medical expertise prevented malaria from exerting evolutionary pressure.
- Statistically, 4th generation Australian males are marginally shorter than their great grandfathers. It is thought that this is because a very large fraction of Australian males served in the trenches in World War 1 - the taller you were, the more likely you would get a bullet in the head. This is another form of evolution in action, but it doesn't change the big picture. Post war immigration is cancelling it out.
- Here's another example: AIDS is very prevalent in the younger indigenous population in remote areas of Australia, and the government can't figure out what to do about it. Unless they do, evolution will kick in one way or another. And no, I DON"T think this is an acceptable situation. It most certainly is not. Again it is an special case that doesn't alter the big picture - over the whole population of Australia, AIDS is extremely rare and thus is of negligible evolutionary pressure.
- I can think of more examples like this. There's probably lots and lots of them - localized special cases that don't make any difference to the human population at large.
- I DID NOT say that we do wrong by helping the unfit. That's a moral issue that is quite separate from what I did say, which was that we do help the unfit and that prevents evolution from being effective.
- Yes, A-law and mu-law are variations of companding of the general class of log-antilog non-linear companding that I described. Unlike Dolby and other forms of gain companding (there were once many), overloading can only occur if the signal amplitude exceeds the input dynamic range of the encoder.
- I have no particular interest in PSQM. Thank you for mentioning "obvious expertise". One hopes that one is competent in their chosen field.
- Sound pre-masking is due to the way our memory works. It applies to all senses. Sudden unexpected severe events or trauma causes loss of memory of what happened just before. Anything that demands 100% mental attention prevents the storage of immediately preceding unimportant events.
- Why on earth would I create an account on Wikipedia? I don't feel welcome. Nil einne is not welcoming. He thinks I should be banned, whatever that means. It seems that every functional page in Wikipedia has a talk page. I've had a browse, and it seems to me Wikipedia is infested with trolls and vandals. And others who seem to invest an awful lot of time attacking others, and endless debate without result, instead of engaging in constructive debate like yourself. If you want to know what's welcoming and constructive, try diyAudio.
- Bye118.209.48.233 (talk) 02:48, 5 August 2018 (UTC)Reply
I'm not particularly interested in this discussion hence why I ignored it until now. Note that never said I think you should be banned. I said you are already topic banned. In fact, I said I specifically said I think you had fair chance of having the topic banned overturned if stopped socking, then after a few months created an account and agreed to stick with it and asked for the topic ban to be overturned. As you well know the reason you were topic banned is because you misleadingly pretended to be multiple people to try to bolster yourself on the RD. In fact, you could create an account right now and edit anywhere else other than the RD and wouldn't need to tell anyone about it since you were only ever topic banned from the RD. For that matter, you don't have to create an account to edit anywhere other than the RD if you don't want to, although I'm not sure if it's likely to help you get your topic ban lifted. Not because it's illicit for you to do so, but because edits from your IP aren't going to provide good evidence that you will stick to one account. But then again who knows, maybe if you genuinely left the RD for a few months, you will be able to get your topic ban lifted without creating an account provided you agree not to pretend to be different people any more. I'd also note that your point about evolution does not address what I referred to. WW1 and modern medical treatment strongly postdate the stone age or cave age. The first known time when Quinine was used to treat malaria was in 1631. And while not directly something you referred to, the Germ theory of disease only came about after 1564 again long after the stone age or cave age. In other words, even if modern medical treatment etc have 'stopped' evolution, which itself is something many evolutionary biologists would reject or say is too simplistic and based on a misunderstanding of evolution, this doesn't tell us that it stopped in the cave age or stone age which was your contention that I disputed. It's very likely the primary reason why Human genetic resistance to malaria is not more widespread is not because human evolution (essentially or whatever you want to say) stopped in the stone age or cave age thanks to modern medical treatment arising a long time later. It's very likely the main reason is the fact malaria is much more significant problem in warmer humid climates (or in some cases was only spread recently e.g. [13]). There's a good chance that in quite a number of areas, genetic resistance is decreasing in part because a combination of medical treatment and mosquito control has reduced the cost of malaria to the population compared to the cost of the genetic resistance (which often has a cost of its own). Of course when populations move around, this would also have an effect on the selective pressures that apply. Our article notes that sickle cell disease and trait appears to be less common n the African American populations than the populations that populations that they may have originated from although as it also notes, there could be quite a lot of reasons. (Genetic testing is also likely to have an effect.) The wider issue is that of course, none of this tells us anything about whether there could have been a sufficiently strong selective pressure that applied to a large percentage of the human population to cause a wide spread change for some specific trait since the stone age or cave age. Assuming that something can't be evolutionary because you think the selective pressure only arose after the stone age or cave age and evolution stopped in the stone age or cave age thanks to modern medical treatment millennia later (or whatever you were trying to say) is just silly and one of the reasons why evolutionary biologists generally feel such statements, whether or not you add words like 'essentially', are too simplistic. Nil Einne (talk) 13:19, 2 October 2018 (UTC)Reply
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