In a blind test, audiophiles couldn't tell the difference between audio signals sent through copper wire, a banana, or wet mud — 'The mud should sound perfectly awful, but it doesn't,' notes the experiment creator

A moderator on diyAudio set up an experiment to determine whether listeners could differentiate between audio run through pro audio copper wire, a banana, and wet mud. Spoiler alert: the results indicated that users were unable to accurately distinguish between these different 'interfaces.'

Pano, the moderator who built the experiment, invited other members on the forum to listen to various sound clips with four different versions: one taken from the original CD file, with the three others recorded through 180cm of pro audio copper wire, via 20cm of wet mud, through 120cm of old microphone cable soldered to US pennies, and via a 13cm banana, and 120cm of the same setup as earlier.

Initial test results showed that it’s extremely difficult for listeners to correctly pick out which audio track used which wiring setup. “The amazing thing is how much alike these files sound. The mud should sound perfectly awful, but it doesn't," Pano said. "All of the re-recordings should be obvious, but they aren't."

This is quite surprising, especially as we often don’t think of bananas, or even wet mud, as great conductors. However, the tester surmised that introducing the materials into the circuit is just like adding a resistor in series, and they’re unlikely to distort the audio too much, except by lowering the signal level.

After waiting a month for testers to submit their results, the following results were tabulated:

As we can see in the image above, there are only six correct answers out of 43 guesses. We put these numbers in a spreadsheet, which showed that only 13.95% of the answers were correct. Furthermore, we used the binomial distribution formula and determined there’s a 6.12% chance that we’d get the same or fewer correct answers if the listeners were randomly guessing — slightly above the 5% significance threshold many statisticians use, meaning the results are consistent with randomness. This goes in line with Pano's conclusion that "listeners can't reliably pick out the original from the looped versions," suggesting that they cannot detect any changes introduced by the loop — whether it's pro-grade copper wire or wet mud from somebody's backyard.

Pano came up with this idea after they watched a documentary, Amigo, where the U.S. Army was setting up a singular telegraph wire in the Philippines. They thought that it wouldn’t work as “you need two wires to complete the circuit.” However, it turns out that the telegraph system used the earth as a return, even through long distances. This got them thinking that if you could send telegraphy signals across the ground, what would an audio signal using the same medium sound like? They then tried various materials like mud and banana, which, although they’re pretty poor conductors, still seemed to introduce imperceptible changes to the signal, at least for the average person.

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