In signal compression, the ratio of the dynamic range of compressor input signals to the dynamic range of the compressor output signals. Note: The compression ratio is usually expressed in dB. For example, a 40-dB input range compressed to a 30-dB output range would be equivalent to a 10-dB compression. 2. In digital facsimile, the ratio of the total pels scanned for the object to the total encoded bits sent for picture information. 3. The ratio of the gain of a device at a low power level to the gain at some higher level. Note: The compression ratio is usually expressed in dB.