ABSTRACT
Speech perception involves the process of decoding a message from the stream of sounds coming from the speaker. Speech is considered as a summation of a number of frequency bands with amplitude-modulated signals. This chapter addresses the question of which frequencies in the temporal envelope of the speech signal are important for intelligibility. The envelope itself is a complex signal that can be analyzed in terms of temporal modulation frequencies. The chapter presents a series of experiments to assess the effect of reducing certain temporal modulation frequencies on sentence intelligibility and phoneme recognition. For the evaluation or prediction of speech intelligibility with various types of transmission channels, the modulation transfer function concept has led to the development of the speech transmission index. The effects of temporal envelope filtering cannot be studied properly when signal processing is performed on wideband speech.
