Ananya Sen Gupta – ananya-sengupta@uiowa.edu
Department of Electrical and Computer Engineering
University of Iowa
Iowa City, IA 52242
United States
Trevor Smith – trevor-smith@uiowa.edu
Panchajanya Dey – panchajanyadey@gmail.com
@panchajanya_official
Popular version of 5aMU4 – Exploring the acoustic color signature paterns of Bansuri, the traditional Indian bamboo flute using principles of the Helmholtz generator and geometric signal processing techniques
Presented at the 188th ASA Meeting
Read the abstract at https://eppro01.ativ.me//web/index.php?page=Session&project=ASAICA25&id=3848014
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
More media files accessed here
Bansuri, the ancient Indian bamboo flute, is of rich historical, cultural and spiritual significance to South Asian musical heritage. It has been mentioned in ancient Hindu texts dating back centuries, sometimes millennia, and is still played all over India in classical, folk, movie songs, and other musical genres today. Made from a single bamboo reed, with seven finger holes (six are mostly played) and one blow-hole, the Bansuri carries the rich melody of wind whistling through the tropical woods. In terms of musical acoustics, the Bansuri essentially works as a composite Helmholtz resonator, also known as wind throb, with a cylindrical rather than spherical and partially open cavity. The cavity openings are through the finger holes that are open during playing, as well as the open end of the shaft. Helmholtz resonance refers to the phenomenon of air resonance in a cavity, an effect named after the German physicist Hermann von Helmholtz. The bansuri sound is created when the air going in through the blow-hole is trapped inside the cavity of the bamboo shaft, before it leaves primarily through the end of the bamboo shaft as well as the first open finger holes.
The longer the length of the effective air shaft, which depends on how many finger-holes are closed, the lower the fundamental resonant frequency. However, the acoustical quality of the bansuri is determined not only by the fundamental (lowest) frequency but also by the relative dominance of the harmonics (higher octaves). The different octaves (typical bansuri has a range of thee octaves) can be activated by the bansuri player by controlling the angle and “beam-width” of the blow, which significantly impacts the dynamics of the air pressure, vorticity and air flow. A direct blow into the blow-hole for any finger-hole combination activates the direct propagation mode, where the lowest octave is dominant. To hit the higher octaves of the same note, the flautist has to blow at an angle to activate the other modes of sound propagation, which proceeds through the air column as well as the wooden body of the bansuri.
The accompanying videos and images show a basic demonstration of the bansuri as a musical instrument by Panchajanya Dey, simple demonstrations of a glass bottle as a Helmholtz resonator, and exposition of how the acoustic color (shown in the figures) can be used to bridge interdisciplinary artists to create new forms of music.
Acoustic color is a popular data science tool that expresses the relative distribution of power across the frequency spectrum as a function time. Visually these are images with colormap (red=high, blue = low) representing the relative power between the harmonics of the flute, and a rising (or falling) curve within the acoustic color image indicates a rising (or falling) tone for a harmonic. For the bansuri, the harmonic structures exist as non-linear braid-like curves within the acoustic color image. The higher harmonics, which may contain useful melodic information, are often embedded against background noise that sounds like hiss, likely from mixing of airflow modes and irregular reed vibrations. However, some hiss is natural to the flute and filtering it out makes the music lose its authenticity. In the talk, we presented computational techniques based on harmonic filtering to separate the modes of acoustic propagation and sound production in the Bansuri, e.g. filtering out leakage due to mixing of modes. We also exposited how the geometric aspects of the acoustic color features (e.g. harmonic signatures) may be exploited to create a fluid feature dictionary. The purpose of this dictionary is to store the harmonic signatures of different melodic movements, without sacrificing the rigor of musical grammar, or the authentic earthy sound of the bansuri (e.g. some of the hiss is natural and supposed to be there). This fluid feature repository may be harnessed with large language models (LLM) or similar AI/ML architecture to enable machine interpretation of Indian classical music, create collaborative infrastructure to enable artists from different musical traditions to experiment with an authentic software testbed, among other exciting applications.