The diagram is a screen shot from audio-editing software showing a graphical display of sounds. In this display the horizontal axis represents time. The sounds are shown as solid blocks of green. The height of the block represents the sound’s amplitude and its width represents its duration. Each block of sound is labelled with a letter. The letters go from A to I.
The first sound shown is a tall block of short duration, labelled A. This is two seconds of the 440 hertz masking tone. After this sound there is a short period of silence, and then a very shallow sound labelled B. This is two seconds of the quiet 652 hertz masked tone. This is followed by a short gap of silence.
The next sound is as tall as the first and is labelled C. This represents four seconds of the 440 hertz masking tone. This merges into a very slightly taller section labelled D, which consists of both the 440 hertz masking tone and the quiet 652 hertz masked tone. After four seconds the amplitude of this sound decreases over a period of about four seconds. This period of decreasing amplitude is labelled E. The amplitude decreases to the level of B, the 652 hertz masked tone, indicating that the 440 hertz masking tone has been reduced to zero, leaving just the 652 hertz masked tone.
The next section is F, and merges with E before it. It represents the 652 hertz masked tone. After four seconds of this, the amplitude of the block gradually gets bigger, indicating that the 440 hertz masking tone is brought back in and increases in volume. This part is labelled G. The amplitude reaches the same value as section D, and stays at this amplitude for four seconds. This section is labelled H. After four seconds the amplitude drops very slightly, indicating that the 652 hertz tone has dropped out leaving just the 440 hertz masking tone. This section is labelled I.