The ear’s frequency selectivity worsens as frequency rises above 500 Hz.

Evidence

Fletcher also noted that the size of the critical band tended to increase with increasing frequency. Data that illustrate the bandwidth of the critical band are plotted as a function of frequency in Figure 3–9. For frequencies up to about 500 Hz, the size of the critical band is fairly constant, but then it increases with increasing frequency. As a result, frequency selectivity of the ear is not constant and gets worse as frequency is increased, as long as frequency selectivity is characterized in terms of hertz. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 477