Dictaphone, recoding unit. Belonge to Baldi. About 1937.

Professor Baldi used this audio recorder for dictating his scientific memoirs, later typed by a secretary. The name "Dictaphone", registered by the Columbia Graphophone Company in 1907, soon become the common term to refer to this device, especially in his version using wax-coated cylinders as recording support. The voice recording was obtained exploiting the vibrations of a membrane caused by the sounds. The membrane was fixed a metal pin affecting the surface of a wax-coated rotating cylinder. To reproduce the sound, the metal pin was slid along the groove engraved before, causing the membrane vibration and the sound reproduction.