At 1000 Hz humans detect frequency changes of about 0.2 percent

Evidence

Exceptional sensitivity. The frequencydiscrimination data shown in this figure indicate that humans have an exquisite ability to tell when two tones have different frequencies. At a moderate stimulus level (e.g., 40 dB sensation level), the FDL at 1000 Hz was roughly 2 Hz. Thus, we can hear a change in frequency approximately 2/1000ths of the reference frequency, or 0.2%! — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 1261

Categorization

• CANDY: A 0.2% frequency-change sensitivity is a fun, tweetable precision-engineering fact about the ear.
• XREF: Connects to Weber-fraction psychophysics in other perception domains (vision contrast, weight discrimination).