ITDG calculation with a non linear iterative algorithm

The role of the Initial Time Delay Gap (ITDG) is well known in relation to subjective perception of a concert hall. Beranek related the ITDG value to subjective attribute of “intimacy”, on the basis of on listener's judgement statistics. Ando found a relationship between ITDG, diffuseness and factors extracted from short time autocorrelation function of the sound signal. Ando identified the ITDG as one of the four normal factors contributing to the subjective preference in a concert hall. In order to clarify the role of the ITDG in the subjective perception of a concert hall a correct measurement method is needed. In the present work, the energy distribution instead of the hall geometry is used as criterion of choice of the significant reflection. The ITDG is assumed as the delay of the reflection group with the maximum energetic contribution instead of the reflection with the maximum of amplitude. An efficient algorithm for the extraction of the ITDG value is presented. The algorithm is based on an iterated non linear processing and on a short time squared integration. Impulse responses measured in two different auditoria have been used for testing the efficiency and the robustness of the proposed method.