Frequency JND is best around 500 Hz at about 0.3 percent

Evidence

As shown in the previous section, tones presented alone evoke the highest pitch salience, where the frequency of the tone defines the pitch in general. Thus, to get an idea of the best performance of hearing with pitch, measuring the smallest perceived change in the frequency of the tone f = |f1−f2|, where f1 and f2 are the frequencies of two tones presented in succession to the subject, is of relevance. f then characterizes the JND of pitch. The result of such a measurement is shown in Figure 10.2. At the frequencies 250 Hz and 500 Hz, the JND is about 1 Hz, and it rises quickly to 200 Hz for 8-kHz tones (Sek and Moore, 1995). The same result plotted as a ratio with tone frequency is shown in the right panel. This shows that the ratio is at best about 0.3% and clearly rises at frequencies above 2 kHz; it also seems to rise at frequencies below 500 Hz. The poorer relative JND at higher frequencies can be explained simply by the neural loss of phase synchronization, while at low frequencies the decreasing sensitivity of hearing explains the degrading results. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1084

Categorization

• XREF: Relates to neural phase-locking limits, which connect to the broader theme of how auditory nerve firing encodes frequency, relevant to cochlear implant and hearing-aid signal processing design.
• QUESTION: Why does relative JND rise again below 500 Hz if sensitivity is still strong there — what exact mechanism of decreasing sensitivity at low frequencies produces this?