An excellent undergraduate student, Jieun Oh, from Jonathan Berger's music perception and cognition class, found a brilliant paper by Bruce A. Young (2003; reference provided at the bottom of this page). In this paper, the author says snakes do hear sounds from their inner ears. When we found the auditory curve of snake hearing (Figure 1), Jonathan said, "Can you synthesize what snakes hear?" and I said, "yeah, it seems like a simple low-pass filter," (Figure 2) which turned out to be 6 hours of parameter tweaking of a custom designed four-zero two-pole IIR filter, and a 512th order FIR low-pass filtering (fft-convolved), which are cascaded to mimic the snake auditory response.
According to Young (2003), this kind of snakes hear only from 100 Hz to 700 Hz, with a peak gain at 300 Hz. I made a filter to mimic this reponse (Figure 3). It has strong attenuation for high frequencies more than 700 Hz. While I achieved the good fit of the shallow curve on the filter of pass-band as close as snake hearing curve, I did not work intensively on the attnuation of below 100 Hz, since humans don't hear much from the low frequencies, plus most of speakers cannot reproduct those low ranges anyways.
I am going to develop this website more eventually, but first I wanted to share the sounds with my friends and colleagues, so I simply upload the frequency response of the filter, and the sound files.
What we found interesting: In the fourth sound example, our simulation tells that snake mostly listen to the lion voice, but not much of monkey and peacock voices. As detectives of the mystery hunt, we fantasize if it could hint anything about the evolutionary process, e.g. lions being more of serious danger to snakes than peacocks or monkeys? Although we cannot (and should not) stretch this simple synthesis to any critical discussion at this point, it may be a good start of such thoughts.
Snake Charmer Song
Snake hearing Snake Charmer Song
Lion, peacock and monkey in a zoo
Snake hearing Lion, peacock and monkey in a zoo
Figure 1: Snake Hearing Curve, from (Young, 2003)
Figure 2: Snake hearing curve inverted: this is the goal of the filter design.
Figure 3: Snake Auditory Filter Response