Frequency Specificity Of Narrowband Chirps And 2-1-2 Stimuli: Spectral Analyses

ObjectiveThe current study examined the frequency specificity of NB chirps by comparing the spectral characteristics of 500-, 1000-, 2000- and 4000-Hz NB CE-Chirp(R) LS stimuli with those of 2-1-2 tones. DesignSpectral characteristics including the centre frequency, bandwidth, and stimulus energy changes after stopband filtering were compared. The bandwidth was computed as the difference between the upper and lower frequencies at -20 dB (& -3 dB) cutoff points of the main lobe; the centre frequency was determined as the geometric mean of the upper and lower frequencies at the -20 dB (& -3 dB) cutoff points. ResultsAt 100 dB peSPL, the bandwidths of the 500-, 1000-, and 2000-Hz NB CE-Chirp(R) LS acoustic spectra were 1.7-2.5 times wider than the acoustic spectra for the 2-1-2 tones; the 4000-Hz NB CE-Chirp(R) LS bandwidths were 1.4-1.6 times wider than those of the 2-1-2 tones. The energy of NB CE-Chirp(R) LS stimuli was concentrated within {+/-}0.75 octave of the centre frequency, compared to {+/-}0.5 octave for 2-1-2 tones. ConclusionNB CE-Chirp(R) LS stimuli demonstrated poorer frequency specificity compared with 2-1-2 tones. Further studies are needed to investigate the place specificity of the ABRs to NB CE-Chirp(R) LS before implementing them clinically.