By mid-April 1877, Charles Cros had realized that a phonautograph recording could be converted back into sound by photoengraving the tracing into a metal surface to create a playable groove, then using a stylus and diaphragm similar to those of the phonautograph to reverse the recording process and recreate the sound. Before he was able to put his ideas into practice, the announcement of Thomas Edison's phonograph, which recorded sound waves by indenting them into a sheet of tinfoil from which they could be played back immediately, temporarily relegated Cros's less direct method to obscurity.