The recordgraph system of recording sound on 35mm film was originally developed by Frederick Hart and Company in America during the late 1930s for clandestine telephone tapping purposes. The motors in the recording machines ran continuously, but a clutch only engaged the drive mechanism when sound was present on the telephone line. In this way, the machine could be left to record a week's-worth of telephone conversations on a single loop without needing human attention which might arouse suspicions.

During WWII the machine was developed to give better sound quality so that it could be used for war reporting, its robust construction making it particularly suitable for field use. The D-Day landings were recorded by Recordgraph machines, as were some of the Nuremberg trials.

The loops are made of cellulose acetate safety film, which has to be recorded by the embossing method to give a noise-free background. The cheapness of the medium made this the most economical long-term audio storage of its day, although the machines themselves were relatively expensive, having been built to a very high specification. Follow this link for a more detailed description of the Recordgraph recording system.

Poppy Records has developed a playback system for Recordgraph loops which is superior to the original recording machines. Not only is it capable of better audio quality, but it handles the film more gently and can make allowance for the shrinkage and embrittlement which takes place over the years.