Effect of highpass filtering on the speech transmission index

Highpass filters are commonly used in the signal chain of public address systems. One of the reasons for using a highpass filter is to protect the loudspeaker from unwanted low-frequency signals. In addition, it can increase the intelligibility of speech. In this paper, the effect of the cutoff frequency and order of a highpass filter on the speech transmission index, the crest factor, and the sound level are presented. Analyses were performed for an ideal transmission channel, taking into account reverberation time, interfering noise, and high levels of sound. A computer model of the public address system developed by the author, based on the direct STIPA method, was used. This model enables analyses in the nonlinear range of power amplifier operation, which is often used in public address systems but is not considered in commercially available simulation programs.