The GL6551 is a compander IC to expand dynamic range at transmission/reception systems and to improve the tone quality by means of restricting noise. Two functions are loaded on the IC, the one is the compressor which has the 2/1 ratio of input/output ratio by logarithm, and the expander which has the 1/w ratio input/ output ratio by logarithm. The GL6551equipped with input & filter Amp, DATA IN OUT terminal. The GL6551 is well suited for use in cellular radio MCA and handy telephone set, radio communication systems.