Optimizing pulse-spreading harmonic complexes to minimize intrinsic modulations after auditory filtering

Abstract

All signals, except sine waves, exhibit intrinsic modulations that affect perceptual masking. Reducing the physical intrinsic modulations of a broadband signal does not necessarily have a perceptual impact: auditory filtering can reintroduce modulations. Broadband signals with low intrinsic modulations after auditory filtering have proved difficult to design. To that end, this paper introduces a class of signals termed pulse-spreading harmonic complexes (PSHCs). PSHCs are generated by summing harmonically related components with such a phase that the resulting waveform exhibits pulses equally-spaced within a repetition period. The order of a PSHC determines its pulse rate. Simulations with a gamma-tone filterbank suggest an optimal pulse rate at which, after auditory filtering, the PSHC's intrinsic modulations are lowest. These intrinsic modulations appear to be less than those for broadband pseudo-random (PR) or low-noise (LN) noise. This hypothesis was tested in a modulation-detection experiment involving five modulation rates ranging from 8 to 128 Hz and both broadband and narrowband carriers using PSHCs, PR, and LN noise. PSHC showed the lowest thresholds of all broadband signals. Results imply that optimized PSHCs exhibit less intrinsic modulations after auditory filtering than any other broadband signal previously considered.

Factors limiting vocal-tract length discrimination in cochlear implant simulations

“…Low-noise noises spectrally broader than a critical band also demonstrate slightly reduced fluctuations compared to Gaussian noise, but this reduction does not seem to translate into sizeable psychophysical measurements when a single channel is used (Hartmann and Pumplin, 1988;Hilkhuysen and Macherey, 2014). The PSHC however displays low internal envelope fluctuations even in the broadband case, although again, this has only been tested with a single band (Hilkhuysen and Macherey, 2014). Based on these observations, it might be expected that low-noise noise would not yield smaller F0 JNDs than standard noise while PSHC is expected to.…”

“…To this purpose, other types of carriers have been produced. In the present study we investigated the potential benefits of "low-noise noise" (Pumplin, 1985) and "pulsespreading harmonic complex" (PSHC, Hilkhuysen and Macherey, 2014). Previous studies have shown that narrow band low-noise noises (i.e., narrower than a critical band) have less power fluctuations than Gaussian noise, both in the acoustic signal and at the output of auditory filters (Hartmann and Pumplin, 1988;Hilkhuysen and Macherey, 2014).…”

“…Previous studies have shown that narrow band low-noise noises (i.e., narrower than a critical band) have less power fluctuations than Gaussian noise, both in the acoustic signal and at the output of auditory filters (Hartmann and Pumplin, 1988;Hilkhuysen and Macherey, 2014). Low-noise noises spectrally broader than a critical band also demonstrate slightly reduced fluctuations compared to Gaussian noise, but this reduction does not seem to translate into sizeable psychophysical measurements when a single channel is used (Hartmann and Pumplin, 1988;Hilkhuysen and Macherey, 2014). The PSHC however displays low internal envelope fluctuations even in the broadband case, although again, this has only been tested with a single band (Hilkhuysen and Macherey, 2014).…”

“…In the present study we investigated the potential benefits of "low-noise noise" (Pumplin, 1985) and "pulsespreading harmonic complex" (PSHC, Hilkhuysen and Macherey, 2014). Previous studies have shown that narrow band low-noise noises (i.e., narrower than a critical band) have less power fluctuations than Gaussian noise, both in the acoustic signal and at the output of auditory filters (Hartmann and Pumplin, 1988;Hilkhuysen and Macherey, 2014). Low-noise noises spectrally broader than a critical band also demonstrate slightly reduced fluctuations compared to Gaussian noise, but this reduction does not seem to translate into sizeable psychophysical measurements when a single channel is used (Hartmann and Pumplin, 1988;Hilkhuysen and Macherey, 2014).…”

“…For each frequency band an integer factor k was determined to ensure optimal flatness of the envelope following the values reported by Hilkhuysen and Macherey (2014). In practice, the factor was calculated using a third order polynomial fit to the values of Hilkhuysen and Macherey: …”