Answer

RTA stands for real time analyzer, which is an instrument for measuring and graphically representing the acoustical behavior of a sound system in a room or environment. This function is a built-in feature of a QSC TouchMix digital mixer. Getting an accurate RTA reading requires an omnidirectional microphone with an extended flat frequency response from 20 Hz to 20 kHz. There are a number of manufacturers offering mics especially designed for RTA use.

It is not recommended to use a microphone meant for live sound or other general, non-RTA use. Live sound mics and even recording studio mics are typically directional (e.g., cardioid, supercardioid, hypercardioid, or bi-directional/figure-of-8) and often have frequency response that is tailored for vocals and musical instruments and often also for minimizing feedback. These mics will not give an accurate reading of the room, making it difficult to properly tune the system.