Wikipedia:Reference desk/Archives/Science/2022 December 8

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December 8

Water boiled twice

I've heard that water tastes different after being boiled a second time because all dissolved oxygen has been boiled off. Is there any truth to that? 31.217.44.13 (talk) 05:07, 8 December 2022 (UTC)

Why don't you try it for yourself, and report your findings here? ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:33, 8 December 2022 (UTC)

Fortunately, somebody has already done that, see:

Quality change mechanism and drinking safety of repeatedly-boiled water and prolonged-boil water: a comparative study, which says:

The quality changes of RBW [repeatedly-boiled water] and PBW [prolonged-boil water] show very similar trends that are not as great as might be imagined, and both are impacted by the tap water quality and the physiochemical effects. The dominating physiochemical effects are the water evaporation and the resulting concentration of unreactive components (most dissolved components), which can be easily explained by the existing evaporation-concentration theory.

So any slight change in taste is due to the concentration of minerals and other impurities, caused by evaporation.

Alansplodge (talk) 12:16, 8 December 2022 (UTC)

• See this previous question: Wikipedia:Reference desk/Archives/Science/2010 February 23#Making tea with zingless water. -- Jack of Oz ^{[pleasantries]} 19:50, 8 December 2022 (UTC)

Well remembered Jack. It comes to a similar conclusion but without citing a source. Alansplodge (talk) 22:20, 8 December 2022 (UTC)

It's wrong to say as in that thread that re-boiled water is harmful. People choose not to do it for taste, not health, reasons. 74.64.73.24 (talk) 21:39, 10 December 2022 (UTC)

That's pretty interesting! I can't see any difference in taste but have always thrown it out because boiling the second time won't produce bubbles but dislodges lime chunks. Tap water is very hard here (tastes like evian) but not chlorinated, still I'd rather not get chunks of carbonate in my food & drink (its taste doesn't go well with anything). 31.217.44.13 (talk) 15:15, 9 December 2022 (UTC)

wait, water can be boiled twice? Allaoii ^talk 17:41, 15 December 2022 (UTC)

Implausible sung note

Our article on Tim Storms alleges that he has sung a note of G₋₇, or 0.189 Hz, at which pitch it would need "more than five seconds for the vocal cords to oscillate once".

I'm curious in what sense this can be said to be "singing". What if I just breathe in for 2.5 seconds and out for the same length of time? Am I not generating 0.2 Hz pressure waves, at very low intensity to be sure, but probably more than Storms is getting from his vocal folds? And given that he has time to consciously reshape his larynx during a single cycle, why couldn't anyone do that?

I suspect there's some sense in which the claim is meaningful, but I'm having trouble figuring out what it could be. --Trovatore (talk) 16:35, 8 December 2022 (UTC)

I agree. A 0.2 Hz sound isn't a note, it's percussion. You generate a sound like that merely by hitting a drum every 5 seconds. The effect on the listener would not be a note, but of slowly repeated pulses. Even in the case of a long attack and decay, such a sound would not be recognizable as a pitch. The relationship between rhythm and pitch (which is to say that pitch is just rhythm sped up) is demonstrated to great effect in this video starting at 4:23 by Adam Neely during a lecture he gave a few years back. 12 bpm is even fantastically slow for a practical rhythm, Neely himself makes the case that 33 bpm is the slowest reasonable rhythm for anything described as music. See [1]. --Jayron32 16:46, 8 December 2022 (UTC)

Why is it that if a robot pops bubble wrap at precisely 1,201 beats per minute it makes a continuous note (at least if the bubble to left ear and bubble to right ear travel times are two constants x and y) but the inventor of the sea clock could hear second ticks weren't simultaneous till they were ≤0.02 seconds apart? He'd keep a prototype on each side of the door in the winter to test how long it took the cold one to drift 1 second and in the middle 96/100ths of this time he could tell it didn't sound like when it was simultaneous. Sagittarian Milky Way (talk) 23:57, 8 December 2022 (UTC)

These are quite different scenarios. They can coexist. One is about a rapid steady repetition being perceived as a tone, a quality of the sound. (Does the number 1,201 have a particular significance, or might you as well have written 20 Hz?) The other is about limitations in perceiving differences. What makes you think that this coexistence is in need of an explanation?  --Lambiam 05:02, 9 December 2022 (UTC)

SMW: If you watch the Neely videos like I told you, he actually demonstrates it. In the range between about 10-20 Hz, the sound becomes "confused" and people have a functionally hard time distinguishing between pitch and rhythm. It also is not a hard limit across humanity. In those ranges, different people will "hear" different things depending on factors entirely unique to themselves; but generally pulses below 10 Hz generally are perceived as individual beats (rhythm) and generally pulses above 20 Hz are perceived as pitch, but these are not hard-and-fast. This also depends on the exact characteristics of the sound wave in complex ways. A sawtooth wave and a square wave and a sinusoidal wave will all probably have distinctly different ranges over which they get perceived as separate pulses vs. pitches. Also also, there is a complex perceptive relationship between amplitude and frequency and perceived loudness; generally higher pitched sounds are perceived as higher in volume for the same actual amplitude waves; this is why infrasound is a thing. If you take a note at a certain consistent amplitude, and lower the pitch, it becomes progressively quieter and quieter until it becomes inaudible. Infrasound of the same amplitude as most audible pitches is inaudible to most human ears. If you raise the volume on those sounds, however, to the point where we can hear them, they will sound like individual pulses rather than as a distinct pitch; at least until about the 10 Hz limit... after which it becomes confusing until about 20 Hz. --Jayron32 12:58, 9 December 2022 (UTC)

I can sing at 1.6 μHz, but when I tried to demonstrate that to the Guinness Book of World Records judges, they got impatient and left even before I had gone through the first cycle.  --Lambiam 05:08, 9 December 2022 (UTC)

In acoustics, we have the concept of timbre. A musical note is embodied by a complex sound wave carrying energy at many frequencies, with one prominent fundamental frequency. Perhaps non-obviously, the fundamental frequency need not be the most energetic: if we plot the spectrogram for most musical instruments (and especially for the human voice), we can easily see that even a simple note has many frequencies. We have technical words for some of these aspects: overtones, timbre, resonance, and so on. But it's complicated - it's worthy of an entire library full of explanatory books.

To try to make some sense of it, Here's Fundamental Frequencies, part of the Real Simple Project in computational acoustics at CCRMA, "devoted to the development of musical acoustics laboratory exercises integrating both hands-on laboratory experience and computer-based simulation." If you want to play with Fourier analysis of musical tones, this website provides great resources at zero cost - and it ramps up in mathematical complexity to serve the needs of even the most mathematically analytical signal-processing and music enthusiast!

Just to layer on some complexity, there exist plenty of situations where the sound wave contains zero energy at its fundamental frequency - for certain defintions of the fundamental frequency - because the fundamental frequency can be defined using the spacing of the harmonics, rather than the value of the lowest harmonic. This means that the fundamental need not be the lowest frequency that contains energy, either! This stuff isn't only theoretical nonsense - it has a lot to do with how a human perceives the musical note embodied in a complex waveform. This was demonstrated as a sort of party-trick during a recent episode of QI: identical complex tones were played, and the panelists were asked which notes sounded higher - when in fact this was a soundwave with frequencies specifically constructed to create an ill-posed question! (Addendum: this tone experiment was in Series S Episode 6, Sensational! originally aired on 14 October 2021, also described in this unofficial episode guide. This is the "tritone paradox" and it is has been heavily studied - for decades!)

For "very low frequency" signals - one of my personal favorite topics - the theory can be quite clear, but the signal can be very muddy!

Nimur (talk) 16:30, 9 December 2022 (UTC)

This is also one of those cases where how a physicist defines something differs from how a lay person may define it. All mechanical waves are sound and operate essentially identically regardless of frequency. Human perception on treats a narrow swathe of possible mechanical waves as audible, and human perception also treats different ranges of frequencies within that range differently (see above on the difference between rhythm and pitch). This is almost exactly analogous to the human perception of light, where the visible spectrum is a tiny slice of the range of frequencies of electromagnetic radiation. Humans tend to think of the color yellow as somehow a different phenomenon than, say, their local radio broadcast. It isn't though. They're both just light, though vibrating at different frequencies. Same thing here, whether it is an earthquake or a pulsing drumbeat or a the F above middle C, it's all the same sort of thing. --Jayron32 17:10, 9 December 2022 (UTC)

Also to Nimurs point about fundamental frequency, timbre, and the overtone series, the low notes on a bass instrument, like a bass guitar generally have fundamental frequencies that lie near the limit of human perception. At the amplitudes normally played by such an instrument, the actual fundamental frequency on, say, the low-B string on a 5-string bass probably lies well outside the limit of human perception, unless the instrument is really loud. And yet, our brains do some pretty neat stuff with the overtone series; in with all of the overtones, we will tend to "hear" fundamental frequencies that if played by themselves as a pure sine wave, we would only slightly detect (or maybe not at all, depending on our perception of loudness of that frequency) and yet when played on a bass, our brain "hears" that frequency by "filling in the gaps". Basically, as a psychoacoustics effect, our brain is capable of psychologically "boosting" the lower notes in the context of the overtones. This is also apparent in sound systems that use a subwoofer. When played by itself, a subwoofer often only sounds like a muffled, indistinct, low-frequency sound which is hard to resolve. When played along side of the rest of the sound system, the bass notes become crisper and easier to resolve, however, because when you hear the bass in context of its overtones, your brain is able to better "latch on" to that low sound and resolve it better. --Jayron32 17:20, 9 December 2022 (UTC)

Also also, there's a whole article on this sort of thing at Missing fundamental. --Jayron32 17:22, 9 December 2022 (UTC)

MF is a psychoacoustic effect. If you run an FFT analysers on it the fundamental is missing. In the less interesting case of making a noise that measures 0.2 Hz, anybody can do it as many have posited. Guinness book of records has about as much credibility in the scientific world as Budweiser does in the non American beer world. Greglocock (talk) 05:12, 10 December 2022 (UTC)

Yes, I believe when I said "as a psychoacoustics effect" what I meant was that it was a psychoacoustics effect. Sorry that was confusing to you. Did I clear it up? --Jayron32 12:58, 12 December 2022 (UTC)