I heard a relatively loud single tone followed by a quieter, higher tone. When the two tones were played together, I heard only the louder, lower tone. However, as the lower tone decreased in volume, the quieter, higher tone seemed to fade in until I could hear it clearly. Similarly, as the lower tone faded back in and grew louder again, the higher tone seemed to fade out until I was no longer able to hear it. Thus although the quieter, higher tone was playing all along, I was only able to perceive it when the louder, lower tone was sufficiently quiet.