Some professional-grade amp heads, such as Ampeg's SVT400-PRO, have an audio crossover, an electronic filter that splits the bass signal into a low-pitched signal (which could be routed to a cabinet suited for low-pitched sounds, such as a 1x15" or 2x15" cabinet), and the middle and high frequencies to a different cabinet suited to this register (e.g., a 2x10" or 4x10" cabinet with a horn-loaded tweeter). Amps with a crossover can either have a single crossover point pre-set at the factory (e.g., 100 Hz) or a knob is provided to enable the bassist to select the frequency where the bass signal is split into low and higher-pitched signal. Amps with an adjustable crossover point can enable bassists to fine-tune their speaker output for a particular venue.