Wednesday, March 06, 2019
All The Sound We Can Not Hear
Transom: There’s a very cool sound in an episode of Here Be Monsters. The episode is called “The Bats that Stay,” and in the story Jeff Emtman, the producer, is on a hike with a couple of friends in Colorado. They’re climbing up to a cave nicknamed the Glory Hole in order to see the Mexican free-tailed bats that live there.
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What sounds are extremely difficult for the human ear to hear? What sounds are easy for the human ear to hear? Bats make sounds that are ultrasonic, meaning they produce super high frequencies that the human ear cannot normally hear. I loved the jargon and math within this episode. Also this was such a cool article because I’ve been in production audio for half a semester now and I know exactly what this podcast guy is talking about. Frequencies, and how our lower threshold of hearing is 20 hertz and the highest threshold is 20,000 hertz. Also the fact that this guy talks about Harold Nyquist and how he determined how we hear ranges of frequencies. To hear the bats when he increased his bit rate and the frequencies and to hear that change within the podcast was awesome. He also changed the pitch on his divorce. He could hear the bats and so could we! Which is super cool.
This article was a little weird to me, it seemed to draw some contrasts that just fundamentally don’t exist: namely, the difference between recording audio at high ‘speed’ versus recording with a high sample rate. ‘High speed’ audio recording isn’t really a thing, but if somebody said that to me, I would probably assume they meant recording with a high sample rate. I think the author was basing the language off of ‘high speed’ recording in video, which is actually not that different. By recording at a ‘high speed’ you’re just taking a lot of frames per second, so then when you slow down footage from a high speed camera you’ve still got a usable frame rate while actually playing the video very slowly. The same goes for digital audio. Samples are effectively the audio equivalent of frames in video, it’s just measures over time of voltage from the transducer in the microphone. If you take a lot of measurements in a short period of time, you can play them back slower than you recorded them and still have a usable sample rate that doesn’t cut out the high frequencies. The bat thing was cool, though.
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