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Acoustic Analysis of the Chavín Pututus (Strombus Galeatus Marine Shell Trumpets)

Acoustic Analysis of the Chavín Pututus (Strombus Galeatus Marine Shell Trumpets). Perry R. Cook, Jonathan S. Abel, Miriam A. Kolar, Patty Huang, Jyri Huopaniemi, John W. Rick, Chris Chafe, John Chowning. Chavín de Huántar Strombus Shells.

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Acoustic Analysis of the Chavín Pututus (Strombus Galeatus Marine Shell Trumpets)

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  1. Acoustic Analysis of the Chavín Pututus (Strombus Galeatus Marine Shell Trumpets) Perry R. Cook, Jonathan S. Abel, Miriam A. Kolar, Patty Huang, Jyri Huopaniemi, John W. Rick, Chris Chafe, John Chowning

  2. Chavín de Huántar Strombus Shells • 20 Strombus Galeatus (Cortez Conch) shells discovered in 2001 • Hand worked as “pututus” for musical/ceremonial use: • Mouthpieces • Cutaway of “bell” • Inscribed art patterns, figures, and symbols • Small holes (for lanyard/ hanging/neck-worn)

  3. Previous Work on these Shells • Parker Van Valkenburgh, February 2002, “Style and Interregionalism in the Early Horizon: Twenty Strombus galeatus trumpets from Chavin de Huantar, Peru,” Stanford Honors Thesis (John Rick, Advisor). • John Rick and David Lubman, December 2002, “On the use of Strombus trumpets found at the ancient Peruvian center Chavin de Huantar,” First Pan-American/Iberian Meeting on Acoustics.

  4. Our Task: Measure and Record • Gross measurements • Photographs • Note features (acoustic) • Record lots of audio • Measure volume (1 shell only)

  5. Recording Setup: • 10 E2 Microphones 1 Inside player’s mouth, just behind teeth/lips 1 Just inside shell “mouthpiece” 1 7” inside shell “bell” 1 At bell exit • 6 On principle axes: • Front/Back • Left/Right • Up/Down

  6. Recording (cont). • Sample-synchronous 11 Channel, 48k, 24 bit • Sine sweep room calibration 2x per day (didn’t much matter due to clever DSP) • Multiple runs of: • Toots at • Fundamental F0 • 2nd Harmonic/overtone H2(where possible) • Noise at mouthpiece (no mic1 inside player’s mouth) • Pseudo-random Lip “Fry” at mouthpiece (no mic1) • Palm-slap impulse responses (no mic1) • All files: Edit, Trim, Annotate, Process, Analyze

  7. Sounding Pitch Analysis • F0 detection (Autocorrelation) in 100ms sliding windows on all Toots files Mean/STDEV for each toot once oscillation stable For shells with holes, multiple closed/open conditions were recorded/analyzed

  8. Impulse Response Analysis • Palm-slap (on mouthpiece) closed-bore impulses • Power Spectral Density (PSD) averaged over all impulses • Mark 1st three peaks • Compare open/closed where applicable

  9. Radiation Pattern Analysis • Important for gallery acoustics projects • Normalized Cross-Correlation of (noise) bell mic signal with each distant mic signal: |X4(n)*Xm(n)| ----------------------- where m E [5,10] |X4(n)*X4(n)| • Time window to eliminate wall reflections • Compute/Plot spatial responses in two bands: 0-1k, 1k+

  10. Radiation Pattern (cont): Time Domain

  11. Radiation (cont): Frequency Domain

  12. Radiation (cont): Spatial Domain • NEED THESE!! • Maybe compare an open vs. closed large hole?

  13. Area Function Estimation • Compute LPC coefficients on mic 4 (fry) signal • Compute Partial Correlation (PARCOR) coeffs. • Use Durbin Recursion to generate areas • Assumptions: • Source/filter model • Single waveguide bore (no side chains/holes) • Length? • Fundamental F0 estimates effective length • Mouthpiece and Bell area => exponential factor • Compute for a few length

  14. Areas/Ratios 96 sections (0.66m) 72 sections (0.5m)

  15. Area Functions Useful? • Yes! For “Pathological” Shells: • NEED THIS! Ideally, a shell with no holes (or all holes closed) that doesn’t play so well might exhibit non-constant log area ratios, indicating growth/dirt/diamonds/gold/etc. inside

  16. Shells with no obvious holes:

  17. But many shells have holes in them Small tone-like holes… Or BIG Holes… Affects pitch, playability Affects pitch, quality, radiation pattern

  18. Holey Shells Summary

  19. Conclusions, Questions, Future Work • Are any holes intentional (tone-holes)? • How were these held, and played? • Effects of player’s hand • We know pitch effects, but • Do not know as much about radiation • Other questions? • More physical data to collect, ideally: • Actual length, volume (MRI?) • Same recordings with hand in various positions • Other?

  20. Acks • Cobi Van Tonder: Photo/Videography • Stacie V. Brink: Photography, Metrics, etc. • Jose Luis Cruzado: Photo/Videography, Tech Support • Countryman Associates (Microphones) • Meyer Sound Labs (Reference Test Speakers) • OTHER/OTHER/OTHER/OTHER/OTHER

  21. Please visit and use our data! ccrma.stanford.edu/groups/chavin

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