Aluminum disc

Instead, as the rotating disc passes under the recording head, the sound-modulated vibration of the stylus is embossed into the groove, forming indentations directly upon the metal.

Subsequent vertically-modulated versions fared better acoustically, however their incompatibility with standard home phonographs of the period led to these designs being discontinued in the marketplace fairly rapidly.

In 1934, the Pyral Company in France and the Presto Recording Corporation in the United States independently created the so-called acetate disc by coating a layer of nitrocellulose lacquer onto the aluminum, which now served only as a rigid support.

Made chiefly for the emerging dictation market during World War II, the two most well known are the SoundScriber (vertical modulation) and the Gray Audograph, the latter of which, along with the CGS Rieber unit, recorded in an inches-per-second Constant Linear Velocity mode (like the modern CD/DVD - starting off faster in the center and gradually getting slower as the disc progressed towards the edge instead of recording in revolutions-per-minute.

Cylindrical versions such as the Dictabelt applied the same technology to resin-based loops to get around the decrease of fidelity from the outside to the inside of the disc when recording in RPM/Constant Angular Velocity.