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In the past the "drive rack" for a system included many devices to regulate the system, a crossover to split the signal, an overall system EQ, individual parametric EQs for each crossover band, a compressor to protect the system and a separate installation of all these devices was needed for each "stack" of the system, so for a large concert system a drive rack could be as many as 40u of components to run the front of house system and many more times that amount for running monitors. Digital technology has afforded the ability to house all these components in one simple box that is versatile enough to be used for many purposes with just a change of saved settings instead of requiring total reconfiguration. DSP units offer many features in a single unit, and allow much better system control and protection, the largest innovation being Limiters which can protect a system by preventing the amplifiers from clipping which is the biggest cause of killing speaker drivers. Typical features are:

*Crossover
*Parametric EQ on both inputs and outputs
*Compressor
*Limiter
*Delay
*Dynamic EQ (only kicks in above a certain level, to prevent system characteristics changing as volume changes)
*Phase (switch the phase of the subs relative to the tops to see if it sounds better)
*Many other little handy things you never think you need but now can't live without!

Using a DSP is more complex than an analog crossover but the reward is a much better system in the end. DSPs are excellent pieces of equipment and can save you hundreds if not thousands in saved speakers. Again crossover points are as before, but also you can place a "high-pass" on the system (about 45Hz is fine for most non concert level systems) which saves amplifier power on not reproducing frequencies where there is little sound, and sending frequencies the speakers can't reproduce to them only causes overheating of the speaker and can cause failure. A "low-pass" can be placed on the other end for the same reasons, and about 18kHz is normally fine for this. The other choice a DSP gives is selection of the crossover curves, which allow you to tailor the response for your system, sharper decay curves can give a tighter punchy sound while softer curves can be smoother but too shallow makes the sound muddy.