Introduction to shakuhachi acoustics

Acousticians distinguish between acoustics, the scientifically measurable aspects of sound and psycho-acoustics, the perceived attributes of sound by the human ear. The acoustical values vary from place to place and the psycho-acoustical values vary from person to person. The main elements of acoustics and psycho-acoustics presented in this study are:

  1. The acoustical element of frequency refers to how high or low a sound is and is measured in Hertz. This is called pitch in psycho-acoustical and musical vocabulary.
  2. The acoustical element of intensity refers to how loud or soft a sound is and is measured in Decibels. Intensity is called loudness in psyco-acoustical and musical vocabulary. Our perception of loudness can be influenced by pitch.
  3. The acoustical and psyco-acoustical element of duration refers to how long a sound lasts and is measured in minutes, seconds, etc.

First, we will look at frequency or pitch. Each perceived note is a combination of proportionally related frequencies perceived by the human ear as a single pitch. These related frequencies make up the harmonic spectrum of a sound. In the following example, we can see a fundamental or perceived pitch, middle C, followed by the higher proportionally related pitches or harmonics.

harmonic spectrum of middle C

A sonogram is a representation of the sound envelope or harmonic spectrum (vertical axis) of the sound plotted against time (horizontal axis). The vertical axis show the frequencies measured in hertz while the horizontal axis is measured in seconds. The intensity or loudness of specific frequencies in the harmonic spectrum changes over time. This is represented by the darkness of the line. The physical attributes of harmonic spectrum (frequency and intensity) and sound envelope (harmonic spectrum over time) affect human perceptions of sound. The sound envelope is divided into attack (beginning), steady state (middle of note) and decay (end of note). Our perception of timbre depends largely on the attack at the beginning of a note. It also depends on the makeup of the harmonic spectrum. An important element of shakuhachi tone are the breath and air sounds. A sonogram represents these non-pitched sounds as wavy light grey markings.

There are many limitations to this study:

The sound samples used in this study were recorded using a Pro Tools system in mono and saved in .aiff format using an Apple computer. Then a sonogram or FFT was created by ‘Spear’ (written by Mark Wright and Sami Khoury, The Centre for New Music and Audio technologies, University of California, Berkeley).

Learn more about shakuhachi acoustics by following the links below.