Public address system in the context of "The Who"

In signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a specific range to very low levels. It is the inverse of a band-pass filter. A notch filter is a band-stop filter with a narrow stopband (high Q factor).

Narrow notch filters (optical) are used in Raman spectroscopy, live sound reproduction (public address systems, or PA systems) and in instrument amplifiers (especially amplifiers or preamplifiers for acoustic instruments such as acoustic guitar, mandolin, bass instrument amplifier, etc.) to reduce or prevent audio feedback, while having little noticeable effect on the rest of the frequency spectrum (electronic or software filters). Other names include "band limit filter", "T-notch filter", "band-elimination filter", and "band-reject filter".

A mixing console or mixing desk is an electronic device for mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals from electric or electronic instruments, or recorded sounds. Mixers may control analog or digital signals. The modified signals are summed to produce the combined output signals, which can then be broadcast, amplified through a sound reinforcement system or recorded.

Mixing consoles are used for applications including recording studios, public address systems, sound reinforcement systems, nightclubs, broadcasting, and post-production. A typical, simple application combines signals from microphones on stage into an amplifier that drives one set of loudspeakers for the audience. A DJ mixer may have only two channels, for mixing two record players. A coffeehouse's small stage might only have a six-channel mixer, enough for two singer-guitarists and a percussionist. A nightclub stage's mixer for rock music shows may have 24 channels for mixing the signals from a rhythm section, lead guitar and several vocalists. A mixing console in a professional recording studio may have as many as 96 channels. Consoles used for live sound can go even higher, with some having up to 384 input channels.

In sound recording, a talkback system is the intercom used in recording studios and production control rooms (PCRs) in television studios to enable personnel to communicate with people in the recording area or booth. While the control room can hear the person in the booth over the studio microphones, the person in the booth hears the control room over a PA, monitor speaker, in their headphones or interruptible feedback (IFB) earpiece. Take numbers, reference data, and sometimes count-ins or remarks are also "stamped" onto recordings through talkback, similar to a clapperboard.

A code word is a word or a phrase designed to convey a predetermined meaning to an audience who know the phrase, while remaining inconspicuous to the uninitiated. For example, a public address system may be used to make an announcement asking for "Inspector Sands" to attend a particular area, which staff will recognise as a code word for a fire or bomb threat, and the general public will ignore.

A soundcheck is the preparation that takes place before a concert, speech, or similar performance to adjust the sound on the venue's sound reinforcement or public address system. The performer and the audio engineers run through a small portion of the upcoming show to ensure the venue's front of house and stage monitor systems are producing clear sound, are set at the proper volume, and have the correct mix and equalization (the latter step using the mixing console). When applied to microphones exclusively, it is more commonly (and appropriately) called a mic check.

Sound checks are especially important for rock music shows and other performances that rely heavily on sound reinforcement systems.