Subjective Assessment of the Influence of Room Characteristics on Intelligibility of Noised Speech

A room is a special kind of filter that affects speech intelligibility in two ways. Late reverberation, like noise, reduces speech intelligibility, while early reflections increase speech intelligibility. The influence of the listening mode on the intelligibility of noised speech is also known. Binaural listening is preferable to monaural one because it allows increase intelligibility of speech distorted by noise and reverberation. In this paper, a subjective assessment of the influence of the lecture room characteristics on intelligibility of noised speech during binaural listening was made. The test stimuli were formed in two stages. First, white noise was added to the speech signal which had the form of consonant-vowel-consonant type monosyllable to provide the required signal-to-noise ratio (SNR) in the range from minus 15 dB to plus 5 dB. Then the noisy speech was subjected to two-channel filtration using the binaural room impulse response (RIR) as the impulse response of the nonrecursive filter. Binaural RIRs measured for six different distances from the sound source (from 2.25 m to 10.2 m) in the lecture room of 10.8 × 10.9 × 3.15 m were used. Filtered phrases were listened through headphones, and monosyllables were identified and fixed by means of computer keyboard. The results of articulation tests showed that speech intelligibility is 7-10% higher for distances of 7-10 m than for a distance of 2.25 m with SNR = -10...-5 dB, which can be explained by the useful combined effect of early reflections and binaural listening. However, speech intelligibility for distances of 4-10 m turned out to be less than intelligibility for a distance of 2.25 m with SNR>3-5 dB, which can be explained by the prevalence of the detrimental effect of late reverberation over the action of noise at medium and large SNR values.