A sound source includes: a processor that implements instructions to execute a plurality of tasks, including: a first calculating task that calculates a first estimated value based on a detection result yielded by a detecting device that detects passage of a key through a first, a second, and a third positions, the first estimated value pertaining to behavior of the key at a predetermined position; a second calculating task that calculates a second estimated value based on the result, the second estimated value pertaining to behavior of the key at a fourth position; a signal generating task that generates a first and a second sound signals; a first adjusting task that adjusts an output level of the first sound signal based on the first estimated value; and a second adjusting task that adjusts an output level of the second sound signal based on the second estimated value.