  The detectors of the surface array of the Pierre Auger Observatory are water
Cherenkov tanks. The signals from each tank are read out using three
photomultipliers. The energy of the primary particle is inferred from signal
densities and requires good linearity of the PMTs and a large dynamic range.
The absolute time of arrival of the shower front at each tank is obtained from
the Global Positioning System (GPS) with a resolution of about 10 ns, ensuring
an accurate primary angular reconstruction. Additionally, it is intended to use
the rise time and shape of the signals to constrain the nature of the primary
particle: this sets further requirements on the signal processing. In this
paper, the main features of the signal processing associated with the surface
detector will be presented and its performance will be discussed in the context
of the extraction of shower parameters.
