The second file tests your headphones’ treble extension. To measure your headphones’ highest frequency, play back the second file until you start hearing the underlying (high pitched) sweep tone as it descends. Good headphones will reproduce frequencies up to 20 kHz, the upper limit of human hearing range.

Beware though: 1/ this limit decreases as we age. If all of your headphones suddenly exhibit the same upper frequency limit, and this frequency is lower than what is specified by the manufacturer, suspect your hearing, not the quality of your headphones. 2/ If you hear strange ups and downs or anything else that does not sound like a continuously descending sweep, suspect your sound card and aliasing.