Korg SP-250 User Manual page 26

To check the currently selected temperament, hold down the TOUCH button, and
look at which of the above LEDs is turned on.
Note: When the power is turned on, the equal temperament will be automatically
selected.
About stretched tuning. In order to produce the most natural resonance, PIANO
1 and PIANO 2 sounds use a "stretched tuning" that makes the notes of the lower
range slightly flatter than equal temperament, and the upper range slightly sharper.
This is how an acoustic piano is normally tuned by professional tuners.
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Chapter 4