Based on any audio sample, the shape of the design represents the audio waveform.

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Amazon Mechanical Turk used to be a popular one, but now a number of independent sites are around, such as Death by CAPTCHA. Clever hacks have even been developed for audio CAPTCHAs that merely deconstruct waveform shapes to identify what numbers are being spoken.

FORBES: Artificial Intelligence Will Defeat CAPTCHA -- How Will We Prove We're Human Then?

Users connect their audio source to the player via analog audio input, and the player compares 15 seconds of waveform data with its internal "FingerPrints" database, matching the song up with its corresponding information from MusicID.

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