Abstract: The device of the present invention utilizes a processing principle for time-axis compression-expansion devices which presents variations of reproduction speed from reducing the intelligibility of sounds. Sound signals, without being subjected to any time-axis processing, are altered in frequency while some reduction in intelligibility would be expected to occur, the sound signals are subjected to time-axis transformation processing (compression-expansion processing) to yield reproduced signals of high intelligibility.The present invention is characterized by the capability of making this type of processing available through the use of simple, inexpensive system configurations such as an analog to digital conversion system based on delta/.DELTA. modulation. The speed-changer signal processing circuitry is bypassed automatically when record-playback speeds are the same to avoid processing noise.