Piano Tone Mapping
The piano tone map is a technique developed to provide a graphical illustration of the harmonic structure of a piano's output sound. Each note is recorded individually and then a peak extraction algorithm finds the magnitudes of the harmonics of each note. The magnitudes for each note are then mapped as a surface, which can be illustrated as a colour map. The time reponse can also be illustrated by shuffling a sample window along the length of the recording for each note.
Guitar Tone Maps
Extending the piano tone mapping technique to other instruments requires careful consideration. For an instrument like a guitar notes can be played in multiple positions and the tone can be effected by pluck position, fingering, and plectrum type. In a piano the hammer strike point is fixed and there is only one place to play each note, so it is much easier to ensure consistency in terms of excitation from note to note. The guitar map also comprises a smaller range of notes and major differences can be seen between strings of different types as seen in the steel string guitar for note 39 and above.
Modal analysis is a powerful tool that allows the low frequency vibration of an instrument like the piano to be quantified. The ultimate importance of the modal properties to output sound is questionable, but the results of modal analysis do provide a good basic tool to quantify changes in vibrational properties.
Timbre and Psychoacoustics
Timbre, or sound quality, is an important component of our perception of a musical instrument's sound. Psychoacoustical methods allow quantifiable aspects of a sound to be connecteed to psychological perception, and thus allow us to unite the qualitative world of the mind to the quantitative world of vibration analysis and acoustics. Changes in humidity are anecdotally known to effect the timbre of a musical instrument and it is this hypothesis that is currently being investigated in the guitar.
Wood is an incredibly complex natural material used extensively in musical instruments for its high strength to weight ratio. It poses challenges in the analysis of instruments because of its natural variability and anistropicity. Understanding wood properties, and in particular, their relationship with changes in humidity is an important part of the current research project.