More recently, sound engineers have seen the introduction of dual "fft" (fast-fourier transform) based audio analysis software which allows an engineer to view not only frequency vs. amplitude (pitch vs. volume) information that an RTA provides, but also to see the same signals (sounds) in the time domain. This provides the engineer with much more meaningful data than an rta alone. Also, dual fft analysis allows one to compare the source signal with the output signal and view the difference. This is a very fast way to calibrate a system to sound as close as possible to the original source material. As with any such measurement tool, it must always be verified using actual human ears. Some DSP system processing devices have been designed for use by non-professionals that automatically make adjustments in the system EQ based upon what is being read from the RTA mic. These are practically never used by professionals, as they almost never calibrate the system as well as a professional audio engineer can manually.