This tests that output audio is clamped to 0db maximum. Press each button below in turn. The apparent volume for both should be about equal, even though the second button plays with much higher gain than the first. The resulting waveforms are not equal, however, as the second button audio is clipped to a square wave shape.
The first button plays a square wave with nominal amplitude of 1. That actual amplitude is slightly less than this because the square wave is band-limited which causes ringing, so the amplitude is reduced slightly to prevent overflows due to the ringing.
The second button plays a very loud sine wave of amplitude . This is clipped to unit amplitude so it is approximately equal to a square wave. There will be some buzzing due to the clipping.
WARNING: Full amplitude signals may be loud.