How Spatial Position Affects Piano Tuning 

Over a given time window of measurement, each partial has 3 parameters: Frequency, Amplitude, Phase
A mic position affects all 3 parameters, and most importantly for tuning, the frequency is affected spatially by a spectral tilt induced by the soundboard resonances in the acoustic wave.
The position of a string motion sensor on the wire does not affect frequency accuracy, but only affects amplitude and phase.
The purpose of this experiment:
To show the spectrograms of the partial frequency drifts as observed from each pickup.

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