Sounds on Mars...
As someone who has always been fascinated by the planet Mars (and who even wrote a book, Race the Red Horizon which is inspired by Mars, if not actually set there), the latest NASA Perserverance mission has been breathtaking stuff: not just more pictures of the Red Planet, not just more science, but actual video footage of the thrilling skycrane landing. Amazing stuff.
The Perseverance rover also has microphones on it, which allow us to listen to Mars. The NASA site even allows you to record your voice and hear what it would sound like on Mars. Except, it wouldn't. Not really.
Let me qualify that. If you spoke in an Earth-type atmosphere and the sound of your voice was transmitted to the Martian atmosphere via a loudspeaker, you probably would sound something like the experts at NASA say you would. But if you were actually speaking on Mars, you would sound very different.
The reason is - and this is where my day job comes in - that the speed of sound on Mars is slower than in your vocal tract on Earth: 24,000 cm/s versus 35,300 cm/s. The latter value is an estimate, because there's no such thing as THE speed of sound anywhere: it depends on temperature, humidity, gas mixture. We actually don't know what the average speed of sound in the vocal tract is, and working it out is impossible because all of those factors above vary constantly, but the great Gunnar Fant reckoned it was 35,300 cm/s and calculations I've done with a load of speakers of different sexes and different languages suggests he was about right.
Now, that speed difference matters to the sound of your voice. When you say a vowel like 'uh' (Standard English from England or Aussies/New Zealanders saying the vowel in 'bird') your vocal tract is essentially an unconstricted tube, with resonances like an organ pipe. For vowels, we usually measure the first three resonances and call them formants. For the average adult male with a vocal tract effectively 17 cm long, those formants are around 500 Hz, 1500 Hz, and 2500 Hz; for adult females with a shorter vocal tract they come in higher, at around 600 Hz, 1800 Hz, and 3000 Hz. But they're only at those frequencies because of the speed of sound in air. Lower the speed of sound, as in the Martian atmosphere, and you lower the frequencies of the vocal tract resonances. The vowels sound 'deeper'. That means the vowel 'uh' for an adult male would have the first three formants at 342 Hz, 1027 Hz, and 1712 Hz and sound like it's being spoken by someone with a vocal tract not 17 cm long, but almost 26 cm long! For females the first three formants of 'uh' would be about 400 Hz, 1200 Hz, and 2000 Hz, so even lower (i.e. deeper sounding) than a male voice on Earth!
Of course, I'm simplifying here, because the speed of 24,000 cm/s quoted by NASA is for the dry cold Martian atmosphere, not the warm wet Martian atmosphere as it would be in your vocal tract, which would affect the speed of sound (but maybe not by much: heating makes it faster, adding water vapour slows it down). I'm also ignoring the fact that if you did go to Mars, take your helmet off and say 'uh', it'd be the last thing you did, and you might not even get that far. NASA know that, which is probably why they haven't adjusted the vocal tract resonances, but for those of us who combine an interest in Mars with expertise in speech, it's an interesting idea to speculate about. If we ever terraform Mars, the atmospheric composition won't be exactly Earth-like, and voices will be different inside a base with Earth-type air compared with outside. How different will depend, but you would probably sound taller. And don't even get me started on the speed of sound on Pandora in Avatar, where the taller than human Na'vi still sound like they have human-sized vocal tracts...
The Perseverance rover also has microphones on it, which allow us to listen to Mars. The NASA site even allows you to record your voice and hear what it would sound like on Mars. Except, it wouldn't. Not really.
Let me qualify that. If you spoke in an Earth-type atmosphere and the sound of your voice was transmitted to the Martian atmosphere via a loudspeaker, you probably would sound something like the experts at NASA say you would. But if you were actually speaking on Mars, you would sound very different.
The reason is - and this is where my day job comes in - that the speed of sound on Mars is slower than in your vocal tract on Earth: 24,000 cm/s versus 35,300 cm/s. The latter value is an estimate, because there's no such thing as THE speed of sound anywhere: it depends on temperature, humidity, gas mixture. We actually don't know what the average speed of sound in the vocal tract is, and working it out is impossible because all of those factors above vary constantly, but the great Gunnar Fant reckoned it was 35,300 cm/s and calculations I've done with a load of speakers of different sexes and different languages suggests he was about right.
Now, that speed difference matters to the sound of your voice. When you say a vowel like 'uh' (Standard English from England or Aussies/New Zealanders saying the vowel in 'bird') your vocal tract is essentially an unconstricted tube, with resonances like an organ pipe. For vowels, we usually measure the first three resonances and call them formants. For the average adult male with a vocal tract effectively 17 cm long, those formants are around 500 Hz, 1500 Hz, and 2500 Hz; for adult females with a shorter vocal tract they come in higher, at around 600 Hz, 1800 Hz, and 3000 Hz. But they're only at those frequencies because of the speed of sound in air. Lower the speed of sound, as in the Martian atmosphere, and you lower the frequencies of the vocal tract resonances. The vowels sound 'deeper'. That means the vowel 'uh' for an adult male would have the first three formants at 342 Hz, 1027 Hz, and 1712 Hz and sound like it's being spoken by someone with a vocal tract not 17 cm long, but almost 26 cm long! For females the first three formants of 'uh' would be about 400 Hz, 1200 Hz, and 2000 Hz, so even lower (i.e. deeper sounding) than a male voice on Earth!
Of course, I'm simplifying here, because the speed of 24,000 cm/s quoted by NASA is for the dry cold Martian atmosphere, not the warm wet Martian atmosphere as it would be in your vocal tract, which would affect the speed of sound (but maybe not by much: heating makes it faster, adding water vapour slows it down). I'm also ignoring the fact that if you did go to Mars, take your helmet off and say 'uh', it'd be the last thing you did, and you might not even get that far. NASA know that, which is probably why they haven't adjusted the vocal tract resonances, but for those of us who combine an interest in Mars with expertise in speech, it's an interesting idea to speculate about. If we ever terraform Mars, the atmospheric composition won't be exactly Earth-like, and voices will be different inside a base with Earth-type air compared with outside. How different will depend, but you would probably sound taller. And don't even get me started on the speed of sound on Pandora in Avatar, where the taller than human Na'vi still sound like they have human-sized vocal tracts...
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