The basilar membrane responds preferentially at different points along its length to a narrow range of frequencies, high frequencies at the wide end of the coil and low frequencies in the centre, narrow, end of the coil. This is made a little clearer if you watch the video.
So the output of the cochlea can be modelled as the output of a set of band pass filters each representing the frequency preference of one position on the cochlea.
Digital Filters
A digital filter uses a computer to perform numerical calculations on sampled values of the signal. Numbers, representing successive sampled values of the input signal are multiplied by constants and the results added together. The results of these calculations represent sampled values of the filtered signal and can be converted back to analog form, displayed, and analysed in various ways.
To help us get the idea I have provided a minimal digital filter example. You can copy and paste this in to a Matlab script, playa around with it, and look for further explanation here.
In signal processing, a finite impulse response (FIR) filter is a filter whose impulse response (or response to any finite length input) is of finite duration, because it settles to zero in finite time. This is in contrast to infinite impulse response (IIR) filters, which may have internal feedback and may continue to respond indefinitely (usually decaying). These are sometimes called 'non recurrent' and 'recurrent'. Our example is recurrent.
