An integrated-circuit piano tuner for the equal-tempered keyboard employing a tuneable fixed-coefficient digital filter
Michael William Hagee · Calhoun: The Naval Postgraduate School Institutional Archive (Naval Postgraduate School) · 1969
A study of the physics of the piano reveals that while the upper partials of the steel strings are the eigen-frequencies of the complex tone, they are not integer multiples of the respective fundamentals. To properly measure and tune these eigen-partials, a digital filter capable of sweeping a major portion of the audio-frequency spectrum had to be implemented. Such a filter, a tuneable fixed-coefficient digital filter, is discussed as well as a simple pole-zero design procedure for determining the required coefficients. Each module, including the frequency deviation detector and counter, the time-base generator, the digital filter, the reference frequency generator and the display and control module, of the proposed tuner is illustrated and discussed