cannot generate pure-tone audio

I have a 1-second long WAV file containing an 8-kHz pure sine wave. I import it as a 2D sound, play it from the Inspector, and record the output using a spectrum analyzer. I expect a spectrum with a single line at 8 kHz, but instead get a complex spectrum with lines at many frequencies. The distortion is also audible. As a sanity check, when I play the same WAV file using Windows Media Player, I get the expected single-line spectrum.

Any insight into the source of the distortion in Unity, and how to eliminate it will be much appreciated. Thanks!

You are right. It seems that Unity works in 48 kHz internally and the distortion is caused by resampling.

Try to generate the tone in 48 kHz.