SCOTT SIMON, HOST:
Forty years ago this month, NASA launched a Voyager spacecraft to explore the solar system. It carried a message from Earth that essentially said - hello, out there. This is us. Besides words and drawings, the message included a phonograph record with sounds, voices and music - although none of it from BJ Leiderman, who writes our theme music. That got NPR science correspondent Christopher Joyce and audio producer Bill McQuay to thinking, what would aliens make of the message on Voyager if they found it?
CHRISTOPHER JOYCE, BYLINE: As the Voyager spacecraft cruised by Jupiter, it recorded this.
(SOUNDBITE OF SOLAR WIND BLOWING)
JOYCE: It's the solar wind of charged particles hurtling past the planet, turned into sound we can hear. Voyager's mission was to record what it saw and heard in space. But it also carried a cargo of earthly sounds on a phonograph record made of gold - human speech, music, wind, animal sounds.
(SOUNDBITE OF ARCHIVED RECORDING)
JIMMY CARTER: My dear friends in outer space...
(SOUNDBITE OF MUSIC)
JOYCE: The sound of Earth.
BILL MCQUAY, BYLINE: Now, I'm an audio guy. And I got to wondering, would aliens actually be able to hear this stuff in the first place? I mean, think about it. What if they were aquatic like fish or more like insects? Would they be able to hear the sound the way we do?
JOYCE: So we asked some experts, bioacoustics scientists at Cornell University who study aliens on Earth, animals.
AARON RICE: Everywhere we look at life on Earth, sound is really the universal language of life.
MCQUAY: That's Aaron Rice.
RICE: So I think it's reasonable to predict that if there was extraterrestrial life, they may use sound as a communication channel.
RON HOY: So that's an interesting point, Aaron.
JOYCE: Ron Hoy is also a bioacoustics expert.
HOY: We have to presume that even for these alien lifeforms, evolution was involved.
JOYCE: Evolution of useful traits. And hearing would likely be useful and would evolve, as it has on Earth.
MCQUAY: Yes, but there's all kinds of hearing. The frequency range of hearing varies incredibly from one species to the next based on what they've evolved to listen to. Just take whales for example.
RICE: It ranges from 10 hertz in the songs of blue whales...
(SOUNDBITE OF BLUE WHALE CALLS)
RICE: ...To 200 kilohertz with some of the pygmy and dwarf sperm whales.
(SOUNDBITES OF SPERM WHALES CLICKING)
RICE: And so my suspicion is that if there was some sort of creature that intercepted these sounds, they most certainly wouldn't hear it the way that humans do.
JOYCE: So this was a sort of fun thought exercise. But I figured there's no way to know what aliens would actually hear if they played the Voyager record. But Bill, being the audio guy, found a way.
MCQUAY: I tip my hat to the scientists on this one. They've developed audio filters that actually mimic the way different animals hear.
JOYCE: They use data from tuning curves. These are measurements of the electrical activity in an animal's auditory neuron when it hears a sound.
MCQUAY: Right. You take a sound and send it through a series of filters taken from the animal's tuning curve. Those filters alter the sound to the way an animal would hear it. It's like putting on animals' ears.
JOYCE: OK. Let's say the aliens evolved in water. So what we're going to do is let you hear one of the recordings on the Voyager, Igor Stravinsky's "Rite Of Spring."
(SOUNDBITE OF STRAVINSKY'S "RITE OF SPRING")
MCQUAY: Now, here's what it would sound like if you were a fish, a toadfish.
(SOUNDBITE OF STRAVINSKY'S "RITE OF SPRING (LOW-PASS FILTERED)")
JOYCE: That sounds terrible.
MCQUAY: I don't think the fish would enjoy it.
JOYCE: Hardly music to our ears. We played it for Aaron Rice and Ron Hoy.
RICE: You know, a lot of that almost sounds like environmental noise. So you don't necessarily have discrete notes necessarily like toadfish usually use to communicate.
HOY: I thought that sounded a lot like the early carbon telephone speakers because you lost all the highs.
MCQUAY: That's because toadfishes' ears are tuned to hear lower-frequency sound. It doesn't hear higher frequencies.
JOYCE: Like old rock 'n' roll musicians?
JOYCE: So maybe the Stravinsky would be wasted on a fishy alien. How about something more like an insect-like alien?
MCQUAY: I happen to have tuning curves for several kinds of animals. How about Stravinsky heard by a cricket?
JOYCE: A cricket?
MCQUAY: Teleogryllus oceanicus to be exact.
(SOUNDBITE OF STRAVINSKY'S "RITE OF SPRING (HIGH-PASS FILTERED)")
JOYCE: So that's pretty different from the toadfish - not pretty, but different.
MCQUAY: Ron Hoy happens to be an expert on cricket communication.
HOY: Sweet. I loved it because all those nice high frequencies are there, but the bottom dropped out.
JOYCE: Ron explained that crickets evolved to hear at high frequencies because their mortal enemies are bats, which navigate by using ultrasonic signals. In fact, the Voyager team at NASA asked Ron Hoy, back in 1977, to choose a cricket song for the golden record. He chose...
MCQUAY: Teleogryllus oceanicus.
HOY: I chose it because it had the most complexity. (Imitating Teleogryllus oceanicus song).
MCQUAY: We tried some other music from the record and some spoken English, all pretty unintelligible.
JOYCE: So if aliens evolved like fish or crickets, our message might fall on deaf ears.
MCQUAY: Well, not so fast - if they're flying around in interstellar space, they're probably smart enough to know about tuning curves. They might be able to tune us into their frequency the same way we just tuned Stravinsky out of ours.
(SOUNDBITE OF FREQUENCY FILTER SOUND EFFECT)
JOYCE: So they could make you sound like a cricket, Bill.
MCQUAY: You sound kind of fishy, Chris.
JOYCE: What are you doing, Bill?
For NPR News, I'm Christopher Joyce.
MCQUAY: And I'm Bill McQuay. Transcript provided by NPR, Copyright NPR.