The discrimination of duration was investigated using synthetic vowels with negative intensity changes (0, −6, −12, and −18 dB). Test stimulus durations ranged from 100 to 300 ms in steps of 20 ms and the standard stimulus was 200 ms in duration and had a uniform intensity. Stimulus pairs were presented to 20 subjects whose task was to state which vowel in the pair sounded longer (forced choice; method of constant stimuli). The data indicate that a drop in intensity of more than 12 dB results in a significant decrease in discriminability of duration differences.