Frequency spread in the cochlea is asymmetric with steeper low-frequency slopes

Evidence

For average levels of speech (about 60 dB SPL), a single-peak function has an approximate peak (at −3 dB) of about 1 ERB (or Bark), and the slopes are about 8 dB/ERB (10 dB/Bark) towards high frequencies, and about 20 dB/ERB (25 dB/Bark) towards low frequencies. The closest physiological correlate of the spreading function is the envelope of the vibration on the basilar membrane when excited by a single sinusoid. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1151

Categorization

• DEFINE: Quantifies the auditory spreading function: steep low-frequency slope (20 dB/ERB) versus gentler high-frequency slope (8 dB/ERB), anchored to basilar membrane motion.
• XREF: Connects to masking curve shapes described earlier in the book (Figure 9.6) and to ERB-rate scale concepts — the asymmetry explains why low tones mask high tones more than the reverse.