Editing Sound reinforcement system (section)

==Setting up and testing==
Large-scale sound reinforcement systems are designed, installed, and operated by audio engineers and audio technicians. During the design phase of a newly constructed venue, audio engineers work with architects and contractors, to ensure that the proposed design will accommodate the speakers and provide an appropriate space for sound technicians and the racks of audio equipment. Audio engineers will also provide advice on which audio components would best suit the space and its intended use, and on the correct placement and installation of these components. During the installation phase, audio engineers ensure that high-power electrical components are safely installed and connected and that ceiling or wall-mounted speakers are properly mounted (or "flown") onto [[rigging]]. When the sound reinforcement components are installed, the audio engineers test and calibrate the system so that its sound production will be even across the frequency spectrum.

===System testing===
A sound reinforcement system should be able to accurately reproduce a signal from its input, through any processing, to its output without any coloration or distortion. However, due to inconsistencies in venue sizes, shapes, building materials, and even crowd densities, this is not always possible without prior calibration of the system. This can be done in one of several ways.

The oldest method of system calibration involves a set of healthy ears, test program material (i.e. music or speech), a graphic equalizer, and a familiarity with the desired frequency response. One must then listen to the program material through the system, take note of any noticeable frequency deviation or resonances, and correct them using the equalizer. Engineers typically use a familiar playlist to calibrate a new system. This ''by ear'' process is still done by many engineers, even when analysis equipment is used, as a final check of how the system sounds with music or speech playing through the system. Another method of manual calibration requires a pair of high-quality headphones patched into the input signal ''before'' any processing.{{efn|The pre-fade-listen feature on the test program input channel of the mixing console, or the headphone output of the CD player or tape deck can be used for this purpose.}} One can then use this direct signal as a reference with which to identify any differences in frequency response.<ref>{{cite web |url= http://www.prosoundweb.com/live/articles/daverat/drifting.shtml|title= When Hearing Starts To Drift|access-date=2007-04-26 |last= Rat|first= Dave|archive-url=https://web.archive.org/web/20011226141157/http://www.prosoundweb.com/live/articles/daverat/drifting.shtml|url-status= dead|archive-date=2001-12-26}}</ref>

[[File:Ashly Protea.jpg|thumb|right|A Rane RA 27 hardware [[real-time analyzer]] underneath an Ashly Protea II 4.24C speaker processor (with RS-232 connection)]]
Since the development of [[digital signal processing]] (DSP), there have been many pieces of equipment and computer software designed to shift the bulk of the work of system calibration from human auditory interpretation to software algorithms that run on microprocessors. One tool for calibrating a sound system is a [[real-time analyzer]] (RTA). This tool is usually used by piping [[pink noise]] into the system and measuring the result with a special calibrated microphone connected to the RTA. Using this information, the system can be adjusted to help achieve the desired frequency response.

More recently, sound engineers have seen the introduction of dual fast-Fourier transform (FFT) based audio analysis software, such as [[Smaart]], which allows an engineer to view not only frequency response information that an RTA provides, but also in the time domain. This provides the engineer with much more meaningful data than an RTA alone. Dual FFT analysis allows one to compare the source signal with the output signal. A system can be calibrated using normal program material instead of pink noise or other special test signals. Calibration can be monitored during a performance.