Investigation of the influence of attack and decay parameters on the performance of loudness control algorithm

In acoustics, loudness is the subjective perception of sound pressure. Loudness control systems involving loudness control algorithms are used in radio and television broadcasting. In this paper we present a research on the influence of attack and decay parameters on the performance of loudness control algorithms. Attack and decay are temporal parameters of the algorithm, that define the rate at which the algorithm applies the correction to the audio material. For this investigation, a relatively simple real time loudness control algorithm was devised, having only the two parameters: the attack and the decay rate of the algorithm's reaction. The input signal for the algorithm is the weighted sum of the loudness measurements of the source material the in three temporal scales, as per EBU R-128 recommendation. Experiments were conducted with various summing weights of the input signal. The test sound material was acquired from actual commercial TV broadcast. The performance of the algorithm were evaluated by measuring differences of three parameters of the corrected material before and after the correction as a function of the attack and decay values: the loudness range, overflow percentage, and average integrated loudness level.