Stereophile's Test CD 2 Tracks 30-31
WARNING: TO AVOID DAMAGE TO YOUR LOUDSPEAKERS AND HEARING, DO NOT PLAY THESE TRACKS AT HIGH LEVELS
 19+20kHz at 0dBFS with spoken warning (L+R) (DDD) 0:21
 20kHz at 0dBFS & -20dBFS with spoken warning (L+R) (DDD) 0:31
These tracks will be of no concern to the audiophile who is just interested in music, but will be found very useful to those with a spectrum analyzer. Track 30 tests a CD player or D/A processor for intermodulation distortion—see Stereophile's reviews for more information. While only small children and bats will be able to hear the 19kHz and 20kHz tones, poorly performing CD players and amplifiers will produce audible tones much lower in frequency. Differences from the expected THD+noise differences between the two halves of Track 31 should be related to the amount of jitter in the digital datastream.