The oldest method of system calibration involves a set of healthy ears, test program material (i.e. music or speech), a graphic equalizer, and last but certainly not least, a familiarity with the proper (or desired) frequency response. One must then listen to the program material through the system, take note of any noticeable frequency changes or resonances, and subtly correct them using the equalizer. Experienced engineers typically use a specific playlist of music that they have become very familiar with every time they 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.