A major quest in hearing research over the last 35 years or so has been, and continues to be, how mammalian hearing achieves its remarkable frequency selectivity and sensitivity over a large frequency range, down from 20 Hz up to over 100 kHz in some species. Readers of The Journal of Physiology have had a ringside seat over the years enabling them to follow how this quest has led to the current state of the debate, which is focused on the precise role of the outer hair cells in cochlear tuning and amplification (Dallos et al. 2006; Fettiplace, 2006). How did it all begin? Evans (1972) found that auditory nerve fibres in the guinea-pig were much more sharply tuned than the basilar membrane vibrations that had been reported in the same species. He noted that if the physiological condition of the cochlea was in any way compromised the nerve fibres became less sensitive and more broadly tuned, just like the basilar membrane vibrations. To explain his findings Evans proposed a physiologically vulnerable ‘second filter’, situated somewhere between the broad ‘first filter’ of the basilar membrane and the auditory nerve fibres. The search was on to find the whereabouts of this sharply tuned band-pass filter.