Hearing sensitivity to shifts of rippled-spectrum patterns

Abstract

The sensitivity of human hearing to shifts in rippled spectrum patterns of sound was investigated. The test signal was band-limited rippled noise with spectrum ripples of various frequency spacing and bandwidth; this type of sound may be considered as a quantitatively controlled imitation of complex natural sounds. The listener was required to detect a shift in the spectrum ripple phase while keeping the other parameters of the noise constant. For cosine-shaped ripples, the lowest threshold (1.1%) was found at a ripple frequency of 3.5 ripples per octave (rpo), which corresponds to a ripple spacing of 20% of the center frequency. The threshold increased for both lower and higher ripple densities. Qualitatively similar patterns of threshold dependence on ripple density were observed for center frequencies from 1 to 4 kHz. Making the ripples narrower than cosine decreased the thresholds to 0.7%-0.75% for ripple densities of 2-5 rpo. Keeping the ripple width constant at 3.5%-7.5% of the frequency resulted in a monotonic threshold dependence on ripple density: The threshold decreased with decreasing density (down to 0.7%). An excitation-pattern model explains qualitatively the observed dependence of the ripple-phase shift threshold on ripple pattern parameters.

Discrimination of rippled-spectrum patterns in noise: A manifestation of compressive nonlinearity

“…The envelope of the spectrum was a one-octave wide cycle of a cosine function of log frequency that was centered at 2 kHz (1 oct re 1 kHz, Fig 1A). According to previous studies, this center frequency was characterized by a high resolution of both the ripple density [29, 30] and ripple shift [34]. The cosine envelope was used to avoid the effects of sharp spectrum edges, which might influence the resolution of the ripple patterns [38].…”

“…To generate a reference signal, only one of these two filters was used (either 1 or 2, randomly alternating trial-by-trial) during the 2.4 s. For the generation of a masker burst, one of the filters presented in Fig 1B–1E was used for 2.4 s. The signal and masker were summed. Details of the generation routine have been described earlier [34]. …”

“…In several studies [29, 30, 33], a ripple phase-reversal test was exploited to find the highest resolvable ripple density. In other studies [34, 35], a ripple phase shift was exploited to find the ripple-shift threshold. Contrary to masking-based methods, these tests directly indicate whether the fine spectrum pattern of the rippled-spectrum stimulus is or is not discriminated.…”

Rippled spectrum discrimination in noise: Effects of compression

“…The generation routine was described in detail earlier (Nechaev and Supin, 2013). It affords the absence of wide-band transients at signal onsets, offsets, or spectrum changes.…”

“…Apart from primary spectrum structure (center frequency, shape, and bandwidth), rippled spectra feature a secondary structure: ripple shape, depth, and density within the spectrum envelope. The resolution of rippled spectra in normal listeners was investigated in several previous studies (Supin et al, 1994(Supin et al, , 1998(Supin et al, , 1999Nechaev and Supin, 2013;Aronoff and Landsberger, 2013). It has been demonstrated that both on-and low-frequency maskers deteriorate the resolution of the second rippledspectrum structure (Supin et al, 2001(Supin et al, , 2003Nechaev et al, 2015).…”