Under what sound do people fall asleep easily?

Rhythmic and monotonous sound can easily make people fall asleep, just like the "tick" sound issued by a clock in the dead of night ... The reason is that monotonous and rhythmic sound stimulation, which acts on all points in the same part of the cerebral cortex for a long time, will produce a deep depression process, spread to the whole cerebral cortex and fall to the subcortical part, thus causing fatigue and promoting sleep. ...