Effect of reducing slow temporal modulations on speech reception

Abstract

The effect of reducing low-frequency modulations in the temporal envelope on the speech-reception threshold (SRT) for sentences in noise and on phoneme identification was investigated. For this purpose, speech was split up into a series of frequency bands (1/4, 1/2, or 1 oct wide) and the amplitude envelope for each band was high-pass filtered at cutoff frequencies of 1, 2, 4, 8, 16, 32, 64, or 128 Hz, or infinity (completely flattened). Results for 42 normal-hearing listeners show: (1) A clear reduction in sentence intelligibility with narrow-band processing for cutoff frequencies above 64 Hz; and (2) no reduction of sentence intelligibility when only amplitude variations below 4 Hz are reduced. Based on the modulation transfer function of some conditions, it is concluded that fast multichannel dynamic compression leads to an insignificant change in masked SRT. Combining these results with previous data on low-pass envelope filtering (temporal smearing) [Drullman et al., J. Acoust. Soc. Am. 95, 1053-1064 (1994)] shows that at 8-10 Hz the temporal modulation spectrum is divided into two equally important parts. Vowel and consonant identification with nonsense syllables were studied for cutoff frequencies of 2, 8, 32, 128 Hz, and infinity, processed in 1/4-oct bands. Results for 12 subjects indicate that, just as for low-pass envelope filtering, consonants are more affected than vowels. Errors in vowel identification mainly consist of reduced recognition of diphthongs and of durational confusions. For the consonants there are no clear confusion patterns, but stops appear to suffer least. In most cases, the responses tend to fall into the correct category (stop, fricative, or vowel-like).

Auditory sensory deficits in developmental dyslexia: A longitudinal ERP study

“…The auditory system is very sensitive to amplitude modulation in natural sounds and encodes amplitude modulation across different frequency channels and at different time scales (Joris et al, 2004). Selectively degrading modulation frequencies near the syllable rate (4-16 Hz) degrades participants' ability to identify consonants and to understand sentences (Drullman et al, 1994). In contrast, speech stimuli that are processed to leave only relatively slow (below 40 Hz) temporal modulations enable near-perfect speech intelligibility (Shannon et al, 1995).…”

Basic auditory processes involved in the analysis of speech sounds

“…Nevertheless, it is possible, even probable, that speech analysis makes use of the modulation channels. There is evidence that AM patterns in speech are important for speech recognition (Steeneken & Houtgast 1980;Drullman et al 1994a;Shannon et al 1995). Thus, anything that adversely affects the detection and discrimination of the modulation patterns would be expected to impair intelligibility.…”

Intelligibility and Acoustic Characteristics of Clear and Conversational Speech in Telugu (A South Indian Dravidian Language)

“…However, this does not mean that, when present, the temporal changes of slow clear speech are not important for the intelligibility benefit. Listeners may use the temporal cues when available either to further enhance intelligibility or to process the speech signal in a different manner (weighing available cues differently) [5]. The present data suggest few possible temporal-related mechanisms that may underlie the intelligibility increase.…”