Signal Processors/Rack Effects
A digital signal processor (DSP) is a specialized microprocessor chip, with its architecture optimized for the operational needs of digital signal processing. DSPs are fabricated on MOS integrated circuit chips. They are widely used in audio signal processing, telecommunications, digital image processing, radar, sonar and speech recognition systems, and in common consumer electronic devices such as mobile phones, disk drives and high-definition television (HDTV) products.
The goal of a DSP is usually to measure, filter or compress continuous real-world analog signals. Most general-purpose microprocessors can also execute digital signal processing algorithms successfully, but may not be able to keep up with such processing continuously in real-time. Also, dedicated DSPs usually have better power efficiency, thus they are more suitable in portable devices such as mobile phones because of power consumption constraints. DSPs often use special memory architectures that are able to fetch multiple data or instructions at the same time. DSPs often also implement data compression technology, with the discrete cosine transform (DCT) in particular being a widely used compression technology in DSPs.
Rackmounted effects are typically built in a thin metal chassis with metal "ears" designed to be screwed into a 19-inch rack that is standard to the telecommunication, computing and music technology industries. Rackmounted effects may be one, two or three rack spaces high. When purchased from the store, rack-mounted equipment is not equipped with the rugged chassis features used on stompboxes and amps that are designed to be transported as standalone units, such as corner protectors. Rackmounted units are typically mounted in a rack, which is housed in a road case, a tough plastic case with removable front and rear covers that can be latched on during transportation to protect the knobs and switches and then removed during performances. A rackmount unit may contain electronic circuitry identical to a stompbox's, although its circuits are typically more complex. Unlike stompboxes, rackmounts usually have several different types of effects.
Rackmounts are most commonly used in recording studios and "front of house" live sound mixing situations, though professional musicians who play electric bass, electric guitar, or synthesizers may use them in place of stompboxes, to create a rackmounted head unit for their speaker cabinet(s). Rackmounts are controlled by knobs, switches or buttons on their front panel, and often by a MIDI digital control interface. During live performances, a musician can operate rackmounted effects using a "foot controller". By setting up effects in a rack-mounted road case, this speeds up set-up and tear-down, because all of the effects can be connected together with patch cords (which can be left connected permanently) and all of the units can be plugged into a power bar. This means that a musician only needs to plug in the main power bar into AC Mains power and plug their instrument into the rack, and the last effect unit's output into their instrument amplifier and/or the PA system.
"Shock mount" racks are designed for musicians who frequently move gear between venues. Shock mounts help to protect electronic devices from bumps during transportation. Devices that are less than 19 inches wide may use special "ear" adapters to mount on a rack.