Family Trees, Breezies, and Bats · 12:10pm Oct 8th, 2023
Filly Misty chases a bunnycorn. Ponies walk up glowing paths into a tree. A mysterious market inside a distorted spacetime. A door leads to the Land of the Dragons. Magic has indeed returned to Equestria.
Let’s discuss the Breezie language. Hitch tells us that it is, “pony language, but at too high of a speed for most to understand them.” Zipp shows us that you can decipher it with a simple app. If breezies were, until this point, just a legend, we have to ask how she managed to produce an app to decode their speech so quickly, complete with cute antennae on the button icons. Is it really as simple as just slowing down an audio recording? It is disappointing that this doesn’t work for us. Did anyone else try? Recording sound files and messing around with the speed and other parameter did not reveal anything to me.
Changing the speed of an audio recording is straightforward. You just change the timebase of your digital file. (In the old days you switched the motor speed on your tape player). When you speed it up, you are compressing the rise of fall of every sound wave into a shorter time, so the frequency or pitch is higher, and everyone sounds super-squeaky.
This is not usually what listeners want, so there are now more advanced algorithms to change the pace of an audio sample while keeping the voice pitch the same. This is what you get when you change the Netflix playback speed. Does anyone use this feature? I know some students have found watching recorded lectures at high speed is one way to get through courses taught by dull professors and leave them with a bit more time to play. If you want make the limited supply of new pony episodes last longer, you could watch them at half speed.
Given that breezies are a sort of tiny pony, there is some logic to their different dialect. With smaller vocal cords, they would talk with high-pitched voices, which they would hear clearly through a correspondingly scaled inner ear in those cute little heads. As the breezies don’t seem to be dealing with a lifestyle any more fast-paced than ponies, maybe changing pitch, but not the tempo, of the audio is what you want from a breezy-translator app.
This discussion may seem like an irrelevant over analysis of a cartoon world, just like my other blog posts, but there is a real-world market for gadgets that do this to let you listen to the language of tiny flying mammals—bat detectors.
Bats are fascinating creatures to listen to. They navigate by echolocation—screeching loud bursts of sound, then listening for the faint echo with their sensitive ears. Somehow their batty brains process these data to produce a visual map of the landscape around them, which sounds incredible, but from a different perspective, it’s no more amazing than doing so by analysing reflected electromagnetic waves focussed onto a retina.
These look like some sort of megabat, which don’t use echolocation, but what big ears they have…
Echolocation makes a lot of noise, but as their voices are in the ultra-sound range, beyond our hearing, you need a gadget to hear it.
I built a bat detector when I was aged about fourteen. Unlike most of the gadgets I made at that age, it worked. As that was before fast digital sampling and processing were available to home electronics nerds. It worked like a radio receiver, generating an ultrasonic signal, and mixing this with the input from a sensor, repurposed from a home security system, to convert to the range of our ears. The result is a box with a dial that lets you tune in to the frequency of your bats.
These heterodyne detectors are still a popular choice with bat enthusiasts, although there are now other options. Time expansion detectors work like Zipp’s app by recording a sample and then simply slowing it down by a factor of ten so a 50kHz bat chirp becomes 5kHz and we can hear it. Frequency division detectors divide the frequency of waves in the ultrasound range to give an output that we can listen to in real time.
It is great fun to go outside on a summer evening with a bat detector and listen to their sounds while watching them swoop around chasing insects. As they home in on a mid-air snack, their chirps become much faster and the pitch shifts.
I used to listen to them when I lived in rural Italy. There were lots of old empty buildings in the village where I stayed, providing good bat roosts. Taking an evening passeggiata with a bat detector probably reinforced my reputation as a crazy foreigner. There aren’t so many in my current neighbourhood, presumably because the high demand for property means fewer old buildings with holes in the walls and roof. Maybe more purpose-built bat boxes will help attract them. We could do with more bats (and fewer midges and mosquitos).
I think I need to get a new bat detector for next summer.
Always love learning, thank you.
A very intresting obscure piece of information about pitch shifting is the reason why you cant just sample one note on a pino etc, then simply shift to play back all the other notes.
The harmonics might be integer multiples, but the frequencies are not. They follow a squareroot deviation behaviour from the expected scale.
Now if only I could find that link to the article or at least the book with the graph and algorithm in it.
In the late 80s, early 90s, music programs on the Commodore Amiga handled the problem by having the option of One, Three and Five octave ranges of sampling for each sample, in order to record the harmonic span more accurately. Which must have been quite measureable given the computer only had 8 bit accuracy sound unless certain small channel mixing routine were used, with appropiate error correction arrays to deal with the audio nonliiniarity at that level of accuracy.
Theoretically, the printer port with its 100kHz plus sample rate might be used as a direct sample bat detector, but the electronics mags usually used the beat frequency ultrasonic rangefinder trick?
The Polaroid Autofocus camera used its piezo transducer both for emmiting the ultrasonic rangeing pulse and detecting its return?
This got my Fourier senses tingling.
My comfort zone for speed changes is about 1.25x for Netflix and such, and 1.5 to 1.75 for YouTube productions. So speed-changing apps ought to be a snap!
We've got lots of bats at home; I'd love to have a bat detector... or maybe there's an app for that?
Speaking about bats and pich-shifting, higher frequencies mean better spatial resolution. physics limits the maximumbase-frequency they can generate; so now, most of the energy is not in the base-frequency, but in the subharmoniocs; so no, they use a subharmonic-trick for generating higher pitched sounds than one would expect from the size of their larynches.