A Sound Spectograph is a basic research insrument used in many labratories for research studies of sound, music and speech. It has been widely used for analysis and classification of human speech sounds and the analysis and treatment of of speech and hearing disorders.
A spectograph can also be known as a sonagraph. In 2.4 seconds duration is transferred to the magnetic disk and then sampled as the disk rotates with the recording drum. The stylus passes a spark to the drum, etching the paper.
In the below picture it shows a two second phrase, namely "I can see you." The dark areas show the strong intensity in the spectrum.
