The figure shows a sonagram or “voiceprint” of sounds made by a Bottlenosed dolphin (Tursiops truncatus) showing the simultaneous production of three separate sounds. The darkness of the graph is proportional to sound power. Clicks appear as vertical lines and whistles as more horizontal traces. As you can see, the signals are complex.
Dolphins have a fifth sound channel with a frequency of 130KHz. It is a high intensity, narrow beam directed by the teeth acting as a wave-guide, like an acoustic Yagi antenna. It is likely used for “private” communication at short ranges. We have yet to fully understand how this sound is made.