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Sound-Similar (Free Version) is a lightweight software application that measures the perceptual similarity between two WAV files in Linear PCM format, the most commonly used format in WAV files. The degree of similarity is represented by a similarity score in percentage, from 0% to 100%. The software does not compare the two digital files bit by bit. Nor does it measure the resemblance of the two waveforms. The similarity is rated based on human auditory perception through advanced time, frequency, and time-frequency domain analyses. The resultant similarity score can be used for sound classification as well as perception-based sound quality check. The two WAV files to be compared can have different sampling rates, bit depths, and one or two channels of data. If the file is stereo, then average values of the two channels will be used for comparison. Sound volume difference does not affect the similarity measurement unless it is too low to maintain the perceptible sound quality. The frequency ranges of different classes of sounds, such as human speeches, music and environmental sounds, may be different. Sound-Similar allows the user to specify the comparison frequency range in order to increase the scoring accuracy. It is possible to extend this range to infrasonic or ultrasonic region. There are two comparison modes: (1) Full Length vs Full Length, and (2) Full Length of the Shorter vs Partial Length of the Longer. In both modes, the two WAV files can have different lengths in time. Mode 2 can be used to check whether the shorter is a part of the longer and, if YES, where the shorter is located in the longer. The similarity scoring algorithm in the software has been optimized for general-purpose use. A similarity score below a few percent usually indicates that the two sounds are totally different, while a score from a few percent to 100% often shows that the two are alike with a varying degree of similarity.