Schroeder Integration

Schroeder integration (backward integration) is a mathematical method for converting an impulse response into a smooth decay curve by integrating the squared impulse response backwards from the end of the recording. Introduced by Manfred Schroeder in 1965, this technique produces decay curves equivalent to averaging an infinite number of interrupted noise measurements, making it the standard method in ISO 3382. The resulting curve is free of the random fluctuations that affect individual noise decay recordings. Schroeder integration requires that the impulse response has sufficient dynamic range (signal-to-noise ratio) to produce a reliable decay curve over the evaluation range. For T30 measurements, at least 45 dB of dynamic range is needed. The Lundeby method is commonly used to determine the noise floor cutoff point before integration, preventing noise contamination from biasing the reverberation time estimate.