Tempo (speaking rate) varies both between and within speakers. Such variations in tempo are easily noticeable. But what is the just noticeable difference for tempo in speech? As a first approximation, between-speaker tempo variation is quantified in a sample of similar interviews with 80 speakers of Dutch. Second, the JND is assessed using a somewhat unconventional method, viz. detection of tempo drift. This results in a JND of 15%; it is argued that this value is upwardly biased. Third, the JND is assessed using a conventional same~different pairwise comparison, yielding a JND of about 10%. Tempo variations
between and within speakers typically exceed this JND, and are therefore potentially important in speech communication