👉 A periodograph is a device used for measuring the periodicity of sound waves. It consists of a cylindrical tube with a small hole in it, which is connected to a recording system and a microphone. The microphone picks up sounds that are generated by the moving cylinder, such as footsteps or breathing. The audio signal then travels through the cylinder and reaches the recording device, where it is recorded on a recording tape. The length of the periodograph is the time it takes for one cycle of the sound
