11.2 Frequency discrimination
Some findings indicate that, for moderate loudness levels, humans can detect a frequency change of about 1 to 3 Hz for frequencies up to about 1000 Hz. Figure 37 shows a plot of the smallest frequency difference for which two tones can be discriminated for a number of reference tones. You can see from the figure that up to about 1000 Hz, the DL is between 1 and 3 Hz. In fact, for frequencies between 500 and 2000 Hz, discriminability is a constant fraction of the frequency to be discriminated. In other words, the Weber fraction (ΔF / F) for this frequency interval remains constant, at approximately 0.002. Although this holds true for a wide range of intensities the intensity of the sound does affect the determination of the minimal discriminable change in frequency. The DL for frequency increases as the stimulus intensity decreases. In other words, as the intensity of the sound decreases, it is more difficult to detect it as being different from other sounds close to it in frequency.