Second-order modulation detection thresholds for pure-tone and narrow-band noise carriers

Area of Science:

• Auditory Neuroscience
• Psychoacoustics

Background:

• Traditional modulation perception studies use sinusoidally amplitude-modulated (SAM) signals.
• Second-order temporal modulation transfer functions (TMTFs) assess detection of modulation in the modulation of SAM signals.
• These TMTFs involve a carrier stimulus (frequency fm) and modulation of its depth (at rate f'm), creating spectral components at fm ± f'm.

Purpose of the Study:

• To measure second-order TMTFs using different carrier types (pure tone vs. narrow-band noise) and modulation frequencies (fm = 16, 64, 256 Hz).
• To investigate the role of spectral energy at the envelope beat frequency in second-order modulation detection.

Main Methods:

• Measured second-order TMTFs for three listeners.
• Employed a 5-kHz pure tone or a 2-Hz-wide 5-kHz narrow-band noise as the carrier.
• Varied the modulation frequency (fm) of the SAM signal.

Main Results:

• With a pure-tone carrier, TMTFs were low-pass, with increasing sensitivity and cutoff frequency as fm increased.
• With a narrow-band noise carrier, TMTFs were mostly flat for fm = 16 and 64 Hz, and high-pass for fm = 256 Hz.
• Listeners' performance differed based on carrier type and modulation frequency.

Conclusions:

• Detection of spectral energy at the envelope beat frequency partially contributes to second-order modulation detection.
• Auditory nonlinearities likely generate audible distortion components at the envelope beat frequency.
• Carrier type significantly influences second-order modulation perception.