Author: Rauf Aliev

Exploring the Boundless Spectrum: The World of Animal Hearing | August 29 2025, 17:56

From my notes as I read Ed Yong’s Immense World—

“..It is known that the range of audible frequencies for animals is different from that of humans, but I didn’t realize just how different. Imagine the highest pitch in the world—it would be just under 20 kHz, as it’s considered the upper limit of the audible range. Both the upper and lower limits tend to decrease with age. Most adults can’t hear sounds over 16 kHz. Anything above 20 kHz we call ultrasound.

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So, it turns out that our closest relatives, chimpanzees, can hear up to 30 kHz, dogs up to 45 kHz, cats up to 85 kHz, mice up to 100 kHz, and moths even up to 300 kHz. Imagine, there are so many high-frequency sounds around us, and how rich their sound world is compared to our limited one. It would be interesting to wear headphones that compress the range from 20-40000 Hz to 20-15000 Hz. Many animals, such as mice, actively use ultrasound for internal communication, beyond the hearing range of their predators.

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And when the topic of ultrasound comes up, it’s impossible not to mention bats with their echolocation. Turns out, it’s a wildly interesting topic.”

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Probably everyone knows that bats successfully hunt in caves, where no light penetrates at all, and they don’t crash into stalactites and stalagmites. There’s an English saying, blind as a bat, but actually, they can see. Some species see better, others worse. But let’s talk about echolocation.

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In general, it’s just radar. The bat screams, the sound bounces off a tree, comes back into its ears, and it gets information about how far away the tree is and whether to slow down or not. But the devil, as they say, is in the details. “Engineering” ones.

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Firstly, high-frequency sound attenuates quickly, so you need to shout very loudly for something to bounce back from a few meters away. Beyond that, bats simply don’t “see.” So, they do indeed shout very loudly, and it’s a directed scream. Specifically, they measured 138 decibels, the sound level of a jet engine if you stand next to it. But in the ultrasonic range.

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Secondly, when they scream so loudly, they need to plug their own ears so as not to kill their sensitive apparatus. It turned out that they have special muscles that block the inner ear during the scream.

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Thirdly, both they and their prey are on the move, very fast and erratic. Meanwhile, the speed of sound is about 343 meters per second. The bat’s brain must calculate the difference between the signal and the echo, taking into account both its own movement through space and the movement of the prey. It turned out that the bat’s vocal muscles can contract up to 200 times a second. Moreover, the frequency depends on the phase of the hunt. 200 times—that’s the final phase, when the moth is right in front of the nose, and tiny movements need to be tracked.

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Fourthly, the bat’s brain also has to cope with creating interference between what was shouted out two moments ago and what was shouted out a moment ago. Considering that the sound can echo off the far wall and the near branch. Plus there are waves from the cries of other bats, and they’re usually very numerous in caves. To manage this, they seem to throw a bit different modulation, plus this musculature allows them to “fire” very short pulses—a few milliseconds—and to renew pulses at their own frequency through very short intervals. Imagine what kind of computer in their brains performs the inverse Fourier transform.”

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So, all this works pretty well in small groups. But for example, the Brazilian free-tailed bats live in groups of millions. Really, together 20 million mouths shout something and wait for their echo from the walls and each other. You can’t just pick modulation and frequencies that easily, but somehow they manage. Not perfectly, and if they gather in a really big bunch in the cave, then they perform their commute to the hunt and back to the cave “by memory” – probably due to issues with echolocation. When a “door” was placed at the entrance to the cave, a bunch of bats crashed into it.

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Fifth, consider how they determine distance. It’s necessary to calculate the difference between the signal sent and the signal received (amid a bunch of noise from other bats), and for hunting, it needs to be calculated very precisely. And sound of course isn’t light, but 343 meters per second is also a lot. So studies have shown that bats can recognize differences as little as 1-2 millionths of a second, which allows them to determine distance to fractions of a millimeter. In other words, our eyes are significantly less accurate than their ears.

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Plus, a moth is actually a fairly complex 3D creation that reflects sound differently with its different parts. Otherwise, bats would eat everything that moves. They recognize. In complete darkness. A mouse’s scream contains a whole palette of frequencies, which reflect differently off parts of a moth, and the mouse’s brain somehow manages to translate this into a coherent picture. Moreover, for each of the constituent frequencies, the delay will be its own.

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Then, all this information is layered over time. Roughly speaking, a snapshot from one point is combined with a snapshot from a point a half meter to the right, then from a point half a meter forward, and so on many, many times, which enhances “sharpness” and detail. Overall, it’s the same with us – we only see the spot in front of us clearly while the rest is constructed by the brain. But the brain of a bat weighs 1-2 grams against our half kilogram.

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Think about it, you’re flying with such a built-in radar, and in front of you are two branches at the same distance, which produce essentially the same echo for their ears. And to distinguish them and understand that it’s not one object but two, you really need an advanced brain.

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So, they send pulses lasting 1-20 ms, plus longer pauses between pulses. The pulses are complex in terms of frequencies, so such bats are called frequency modulation (FM) bats. But there are about 160 species that have a much longer cry—many tens of milliseconds but with short pauses, and instead of a complex gamma of frequencies, these use a pure “note.” These bats are called CF—constant frequency. So here’s the thing with these bats—there’s a problem with the Doppler effect, which is an increase in frequency as the distance decreases. Since their brain is tuned to a strict frequency, like 87 kHz for example, they might lose their prey if the echo that reaches their ears is shifted in frequency. And what they do—they shout at a sound speed lower, so that after the Doppler effect it arrives at the correct frequency for the brain.”

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Incidentally, their radar has two modes—forward and downward, the echoes from which are processed separately. The downward radar provides information about position in space, and the forward radar—about the position in space of the prey.

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When I researched the subject, I found that yes, after 20 kHz humans hear nothing, with one exception—frequencies of 2.4 GHz and 10 GHz, which actually belong to the microwave range. Yes, humans can “hear” these frequencies, but not with the ear, but “hear.” This phenomenon is called the microwave auditory effect or the Frey effect. Initially, this effect was registered by people working near radars during World War II, and the sounds they perceived were not heard by others. It turned out that when pulsed or modulated microwave radiation was applied to areas around the cochlea, it was absorbed by the tissues of the inner ear, accompanied by their thermal expansion. In the course of this process, shockwaves are produced, perceived by humans as sound, which no one else hears. It was also discovered that with the appropriate choice of the modulating signal, it is possible to transmit information to a person in the form of individual words, phrases, and other sounds. Depending on the radiation parameters, the sound created in the head can be irritating, cause nausea, and even disable. The volume of the perceived sound can be changed, but acoustic trauma is not possible, as the eardrum does not participate in the process at all. Generally speaking, the method of specifically transmitting sonic messages that are absolutely inaudible to others opens up a whole bouquet of possibilities. I wonder if research is still being conducted on this topic. Google shows that they used to be pretty intense.”

I once published this along with a video, and Facebook reckons that if you publish a video, the text should be one, at most two lines. And in the end, almost no one saw this text. Everyone just watched the video of a bat flying around my apartment 🙂

Cycling for History: A Book and An Unexpected Glimpse into 1930s Migration Trends | August 24 2025, 18:27

I couldn’t resist and bought the book Great Depression in Perceville, VA, where I arrived by bike. I still don’t know how to carry it back for an hour in cycling clothing without a backpack. Interesting note on a random page

Translation:

AMTORG RECEIVES 100,000 APPLICATIONS FOR 6,000 QUALIFIED JOBS IN RUSSIA

(Business Week, October 7, 1931, pp. 32–33)

NEW YORKERS make up the bulk of Americans who have decided, at least for now, to tie their fates with the Russians. Pennsylvania, New Jersey, and Illinois contribute the highest number of applications for the new call for “6,000 qualified workers,” with Michigan, Ohio, California, and Massachusetts also being well represented.

The “Amtorg” office in New York received over 100,000 applications for these 6,000 job slots. Just one morning alone saw 280 applications. All states except ten were represented. Alaska and Panama also contributed one applicant each, and 18 Canadians wanted “to try their luck in Russia.”

Industrial states, naturally, provided the largest number of applications, but others were represented as well. Iowa, Texas, and Idaho also contributed some number of qualified workers.

Since it is widely known that Russia is “industrializing,” most applicants are skilled workers in machinery, railroads, metallurgy, automotive manufacturing, or the construction industry. A look at the qualifications of 280 applicants from one “typical” morning showed that specialists of all professions were looking for work, even if it meant moving to Russia and being paid in rubles. Among them were: 2 hairdressers, 1 funeral director, 2 plumbers, 5 painters, 2 cooks, 36 “clerical” workers, 1 lathe operator, 9 carpenters, 1 aviator, 58 engineers, 14 electricians, 5 salespeople, 2 printers, 2 chemists, 1 shoemaker, 1 librarian, 2 teachers, 1 cleaner and dyer, 11 auto mechanics, 1 dentist.

About 85% of the applicants are U.S. citizens, only 40% of whom were born in the country. 60% of the foreigners primarily come from Eastern Europe. A few African Americans applied, but their numbers are small, as most of them are unskilled workers.

Women constitute only a small portion of applicants, although many wives decided to accompany their husbands in this endeavor. Most workers applying are married and have children.

Three main reasons for wanting to get a placement are named: (1) unemployment; (2) dissatisfaction with conditions here; (3) interest in the Soviet experiment. Almost all foreign workers declare that they do not intend to stay in the USSR. Among engineers, only 10-20% plan to stay.

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This is 1931, one of the most challenging years of that period. Somewhere in the mid-thirties, it started to improve, and it must be said, WWII ultimately defeated it.

Inside Apple AirPods: Design, Battery, and Antenna Secrets Revealed | August 23 2025, 01:52

Very interesting video about how Apple Airpods headphones work (in the comments). You can read about it, or you can just like this post and go check out the original video in the comments. It has pictures!

Battery. 6 hours of operation, but the capacity is only 2% of the iPhone battery capacity. “Dead zones” in the battery, which lead to reduced operating time, can occur due to sudden temperature changes or even just dropping the headphones on the floor. There is a very dense “layered cake” made from a couple dozen layers of anode-cathode. Batteries of fake AirPods or cheap analogs are much worse. Physics: Poor packaging means less active material and fewer lithium ions moving with each cycle => reduced energy density and increased internal resistance => more energy is lost as heat => battery wears out faster.

Antenna. It is located in the stem because the human head significantly dampens the signal. But there is little space in the stem. Metal strip antenna, size 2 mm by 10 microns(!). That’s thinner than human hair. At such size, it cannot maintain shape on its own. In other consumer electronics, antennas can be etched on the printed circuit board, but this limits them to two dimensions. For the AirPod stem, there isn’t enough space. Therefore, Apple uses a clever solution. They embedded the antenna in the surface of a molded plastic cylindrical part. There, clever conductive plastic is used, with added metal. A laser engraves the exact shape of the antenna in the form of small channels with a rough surface. Then, this groove is subjected to electroplating, first with copper, then covered with gold to protect against corrosion. As a result, a durable conductive track is formed, which matches the 3D geometry of the molded part, which would be impossible to create using traditional machining methods. The plastic not only structurally supports the antenna. Other components are attached to it, such as the cable wrapping around the stem to connect the antenna to the Bluetooth chip, the pressure sensor in the stem.

Microphone. In AirPods, not electret microphones, but MEMS: a microelectronic” version of the condenser type. Well, actually, this is not only Apple – any modern TWS headphones, unless they are the cheapest ones. That is to say, modern microphones are made using the same technology as types – photolithography, layer by layer, only in this case it’s a mechanical device, with calculated cavities and flexible layers. Separately interesting is how they make the cavities – they make holes through which etching solution penetrates inside and dissolves the sacrificial layers of silicon dioxide.

Because of such microscopic size, there are several microphones. But why more than one microphone is needed? At the bottom of the AirPods, you will see a small mesh that allows air to enter the second microphone. When you talk, your voice reaches both microphones, but not at the same time. With a difference of only a few millimeters, the chip can detect a delay of six microseconds between when your voice reaches each microphone. This is enough to determine where the sound is coming from and focus on it. Since it precisely knows the distance the microphones are from one another, the chip can compare each signal and amplify your voice during calls.

The third microphone is for noise cancellation. It is located right in front of the speaker, inside your ear.

The microphones consume about 130 mA, which would quickly drain the battery if they were always active. That’s why they are only turned on when you make a call or use noise cancellation. But AirPods are always waiting for a Siri request. How is this possible without constantly active microphones? Here’s a clever solution. Inside the part that is in your ear, there is a small sensor—an accelerometer. It’s the same type of sensor used in phones to determine orientation. But here it serves a different purpose. Instead of measuring orientation, it senses vibration. When you talk, your voice moves through your jawbone. And this vibration is detected by the accelerometer. This low-power consumption signal is enough to wake up the system and activate the microphones when it senses you want to activate Siri. Imagine that, eh?

The sound in AirPods is tuned not “by ear,” but based on a scientific model of the “ideal sound” (Harman curve), which describes the combination of frequencies most people find most pleasing. For this, there is a complicated system of calculated vents and meshes — to control the air flow, which prevents the occurrence of unpleasant “humming” or sharp sounds inside the ear canal. The larger the cells — more air passes through, smaller — less. Such is the mesh, visible as black things on the white earphone—I thought it was for beauty. No, this is exactly that mesh. But at the same time, some kind of moisture protection must be made, and here the mesh is porous. It is claimed that there is some sort of nano-coating that repels water.

Bluetooth. Why it is so immune to interference. Turns out, it uses frequency-hopping spread spectrum technology (Frequency Hopping). Bluetooth devices quickly switch between different channels many times a second and adapt accordingly.

Exploring a Conditional Investment-Based U.S. Visa Program | August 21 2025, 21:23

I wonder if a U.S. visa program would work where specially authorized American investing organizations collectively invest, say, $500,000 in each candidate who files a petition and is ready to pay a hypothetical $20-50K. The money goes to the government, but it returns it monthly with interest. Then, he moves to the U.S., gets a job, and pays back the “investors” from legally earned money, like a student loan. “Investors” help him find a job. If he loses his job, and can’t find another, he can pay from savings for some time, but afterward — he must return home. No savings — go back home. Violated the law (criminal) — go back home. But each such negative case affects whether the “investor” will have the opportunity to invest in new ones.

Investors help with job finding if needed, but there’s no coercion or serfdom, because it doesn’t matter what kind of job the person has, as long as it’s legitimate, and the debt is deducted from the salary. Until the debt is paid, a person’s profile affects the “investor’s” performance indicators, and in case of poor indicators, the investor loses their license or priority.

It’s assumed that, given existing quotas, the “investor” has an interest in finding the smartest and most hardworking people worldwide and subsequently placing them in the local market. If they perform poorly, they simply can’t operate.

After full repayment, he gets the right to citizenship. This could attract talented individuals, support the economy, and ensure responsibility. What do you think?

Uncovering Hidden Hotel Fees: A New York City Experience | August 21 2025, 14:33

Lived in New York on Manhattan for a couple of days recently. The hotel cost 370 USD per day (see photo). Out of which 284 USD is the cost for one day, and the remaining 86 USD are taxes + a mysterious Facility Fee of 35 USD (per day).

From the hotel’s website: “What is a Facility Fee? It’s a hotel service charge! $35 plus tax per day per room provides our guests access to all amenities at Freehand NY, including high-speed WiFi, complimentary 3x filtered water, 24-hour fitness center access, SMART TV connection, priority access to programs and events, and rooftop priority — Broken Shaker!”

Needless to say, these 35 USD were of course not included in the reservation system. It’s not practical to visit every hotel’s website to check for fees before pressing the book button. And yes, the confirmation does state FACILITY FEE TO BE PAID ON ARRIVAL, you can always read and cancel. But for the future, it’s always better to check.

Scam Alert: The Bond Ring Energy Hoax Following My Oura Ring Purchase | August 20 2025, 20:01

I had just bought the Oura Ring 4 when Facebook started running scam ads about the first ring that saps your energy for its own survival. My precious!..

Exploring Shepherdstown: A Hidden Gem in West Virginia | August 20 2025, 13:00

From the trip to Shepherdstown, WV. A small town an hour’s drive from home, founded over 260 years ago. Hardly any tourists, but the few small restaurants and shops compete against each other for the attention and interest of passing travelers.

From the street, there’s an open window at the Lost Dog Coffee cafe. Inside works a very colorful bartender and owner, Garth Emmery Janssen. The coffee shop’s Facebook tagline reads “Founded in 1995 by two crazy punk rockers. We are not normal. We do things correctly. it’s ❤️”

Oat milk latte, please. Dear sir, Garth answers me, that wouldn’t exactly be a latte then. But if you insist, of course. Okay, I say, make it the right way, it doesn’t matter to me. The coffee turned out delicious.

Next, there was an art studio, which I have already written about in previous posts, a handmade cosmetics store where the owner eagerly shares her chemical experiments on the quest for perfect creams and soaps, and where she sells prints drawn by her daughter, who, unfortunately, has grown up and no longer wants to draw.

A very homely atmosphere everywhere. And a nice little town. It lacked modernity, and yes, our regions are all like that, with dust from the past, modernity is somewhat cumbersome.

Decoding “Carboy”: A Journey Through Language and Autobiography | August 20 2025, 04:02

Rereading Feynman’s autobiography, this time in English, and my eyes stuck on the word carboy. It turns out that it’s the same as lady jeanne, and the same as demijohn – essentially lady jeanne in French (dame joanne). In short, it’s just a bottle.