The ratio between the intensities of the direct sound and reverberation. There are several measures for this quantity. C50, one of the most popular, expresses speech clarity as the energy ratio of the first 50 milliseconds of direct sound to the overall steady-state reverberation, with 0 dB being the minimum acceptable value and +4 dB or above preferred. A similar measure, C7, is used in Germany; C35 is yet another version. Measurements are made in a single frequency band (usually centered on 1 kHz). Each of these measures can be more reliable and repeatable than %ALcons, which also deals with the direct-to-reverberant ratio.