The channel in the organ is designed to change the volume of the sound of the pipes.
A feature of organ sound extraction is the inability to change the volume of a single key. If the key can be pressed weaker or stronger on the piano, this will affect the volume of the extracted sound. The device of the organ has only two key positions: full sound or complete silence.
To diversify the sound of organ music, some organ registers are placed behind the channel - special dense wooden blinds that allow you to change the perceived strength of the sound of pipes from the seats of the organ listeners. This subtlety is worth noting: pipes do not play quieter - they are worse heard.
Accordingly, the permeability of the channel flaps can be reflected in the timbre of sound, since different sounds cope with obstacles in different ways. High sound is worse, low is better.
The control of the channel, as a rule, takes place with the feet - a special pedal (not to be confused with the organ pedal - foot keyboard)