(Not to be confused with Autotune) A function of some analog synthesizers that automatically tunes and scales the VCOs (and, in better implementations, the VCFs too) using a built-in frequency reference. In synths that have this function, the auto tune is usually activated automatically at power on. Some synths also have a button on the panel that activates it manually, and of the relatively few analog synths with have both auto tune and MIDI, it is usually possible to activate auto tune by sending the synth a tune request message. Auto tune generally takes 5 to 30 seconds, depending on the tuning algorithm and the number of voices; the function also often includes some means of diagnosing voices that have failed or are too far out of calibration to tune.
The Alesis Andromeda is notable for having an auto tune function that operates continuously in the background. It does an excellent job of keeping the VCOs in tune. In fact, some performers consider it too perfect, and they turn it off.