Experiment Author: Srikanth Nayak
To study the Acoustic change complex (ACC) in the presence of noise, the speech stimulus will be presented in the presence of speech spectrum shaped noise in the background. A speech stimulus (CV) will be presented at 80 dBSPL with continuous background speech spectrum shaped noise at 0 dB SNR. The consonant-vowel (CV) syllable /sa/, an alveolar fricative, will be used as a speech stimulus. The CV syllable will be used to record the ACC because the onset of frication elicits the P1-N1-P2 complex and further the change from frication to vowel elicits another P1-N1-P2 complex. The CV syllable will be presented (80 dB SPL) continuously in quiet and at 0 dB signal to noise ratio (SNR) relative to the peak amplitude of the noise. The speech spectrum shaped noise (Figure) was of 2 sec duration and was synthesized by randomizing the phase of Fourier of the CV syllables and non-speech stimuli used in the study, i.e., it was the long-term spectrum of the aggregate sound files. A narrowband noise was generated by filtering a white noise with a band-pass filter for each of the third-octave bands in this range, and the level of each narrowband noise was adjusted to match the relative magnitude of the long-term spectrum of speech material. The narrowband noise in each band was then summed to generate the speech-shaped noise. The /sa/ stimuli were presented in a homogenous train in the presence of continuous background speech spectrum shaped noise 0 dB signal-to-noise ratio (SNR) relative to the peak amplitude of the noise.