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Impulse Response Evaluation Set Metrics
- Reverberation time: One of the most important metrics used to characterize the subjective impression of a room. This value corresponds to the time that takes the signal to decrease by 60dB. According to ISO3382, this time is obtained by extrapolation to 60dB of a lune fitted to the reverberation curve from -5 dB to -35 dB of decay.
T = 2 * [ T( Lp(-5 dB) ) - T( Lp(-35 dB) ) ]
Since the time decay of the sound does not give an curve precise enough to determine the reverberation time, the Schröder's method is usually used.
- Definition, D: A metric used when judging the suitability of rooms for speech (the first 50ms are useful for speech intelligibility, the rest is detrimental).
with h(t) the impulse response.
- Clarity, C80: A metric used when judging the suitability of rooms for music (the integration time is longer than for the speech because one can allow longer time between reflections without perceiving any echo):
with h(t) the impulse response.
- Early decay time: Extrapolation to 60 dB of the reverberation time during the first 10dB of reverberation decay.
EDT = 6 * [ T0 - T( Lp(-10dB) )]
where T0 equals 0 seconds
- Warmth: Important for classical music. It is dependent on the relative energy between reverberant sound in low and medium frequencies respectively.
where T is the reverberation time.
- Brilliance: Relative energy between reverberant sound in high and middle frequencies using the early decay time.
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