In concert hall acoustics, the ratio, expressed in decibels, of the energy in the first 80 milliseconds of an impulse sound arriving at a listener′s position divided by the energy in the sound after 80 milliseconds. The divisor is approximately the total energy of the reverberant sound.

More generally, clarity refers to the degree to which the separate strands in a musical performance perceptually stand apart from one another.

  • If the clarity is too low, the fast parts of the music are not readable.

  • If there is no reverberation in a room, the music will be very clear and C80 will have a large positive value.

  • If the reverberation is large, the music will be unclear and C80 will have a relatively high negative value.

  • If the early and the reverberant sound are equal C80 goes to 0 dB.

  • For orchestral music, a C80 of 0 dB to -4 dB is optimal.

  • For orchestral rehearsals, a higher clarity of 1d B to 5 dB gives more control over the performances.

  • For vocal performances, the clarity should in the range -4 dB and +4 dB.

  • For speech, in comparison to music, Clarity is measured as the ratio of the first 50 milliseconds (C50) instead of C80.
A long reverberation time adds richness and fullness, but at the same time decreases clarity of articulation. So fullness and richness work against clarity, and a reasonable reverberation time must be reached by an appropriate compromise of clarity versus fullness.

At specific locations in auditoriums, the direct sound may be blocked and so the proportion of reverberant sound versus direct sound reaching the location decreases the clarity.

See also: Apparent Source Width, Haas Effect, Reverberation Time, Sound Definition.

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Subjects: Audio