Acoustic Analysis of the Chavn 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

Chavn de Huntar Strombus Shells20 Strombus Galeatus (Cortez Conch) shells discovered in 2001 Hand worked as pututus formusical/ceremonial use:MouthpiecesCutaway of bellInscribed art patterns, figures, and symbolsSmall holes (for lanyard/ hanging/neck-worn)

Previous Work on these ShellsParker 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.

Our Task: Measure and RecordGross measurementsPhotographsNote features (acoustic)Record lots of audioMeasure volume (1 shell only)

Recording Setup: 10 E2 Microphones1 Inside players mouth, just behind teeth/lips1 Just inside shell mouthpiece1 7 inside shell bell1 At bell exit6 On principle axes:Front/BackLeft/RightUp/Down

Recording (cont).Sample-synchronous 11 Channel, 48k, 24 bitSine sweep room calibration 2x per day (didnt much matter due to clever DSP)Multiple runs of:Toots at Fundamental F02nd Harmonic/overtone H2(where possible)Noise at mouthpiece (no mic1 inside players mouth)Pseudo-random Lip Fry at mouthpiece (no mic1)Palm-slap impulse responses (no mic1)All files: Edit, Trim, Annotate, Process, Analyze

Sounding Pitch AnalysisF0 detection (Autocorrelation) in 100ms sliding windows on all Toots filesMean/STDEV for each toot once oscillation stableFor shells with holes, multiple closed/open conditions were recorded/analyzed

Palm-slap (on mouthpiece) closed-bore impulsesPower Spectral Density (PSD) averaged over all impulsesMark 1st three peaksCompare open/closed where applicable

Impulse Response Analysis

Radiation Pattern AnalysisImportant for gallery acoustics projectsNormalized 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+

Radiation Pattern (cont): Time Domain

Radiation (cont): Frequency Domain

Radiation (cont): Spatial DomainNEED THESE!!Maybe compare an open vs. closed large hole?

Area Function EstimationCompute LPC coefficients on mic 4 (fry) signalCompute Partial Correlation (PARCOR) coeffs.Use Durbin Recursion to generate areasAssumptions: Source/filter modelSingle waveguide bore (no side chains/holes)Length?Fundamental F0 estimates effective lengthMouthpiece and Bell area => exponential factorCompute for a few length

Areas/Ratios96 sections (0.66m)72 sections (0.5m)

Area Functions Useful?Yes! For Pathological Shells:

NEED THIS! Ideally, a shell with no holes (or all holes closed) that doesnt play so well might exhibit non-constant log area ratios, indicating growth/dirt/diamonds/gold/etc. inside

Shells with no obvious holes:

But many shells have holes in themOr BIG HolesSmall tone-like holesAffects pitch, playabilityAffects pitch, quality, radiation pattern

Holey Shells Summary

Conclusions, Questions, Future WorkAre any holes intentional (tone-holes)?How were these held, and played?Effects of players handWe know pitch effects, butDo not know as much about radiationOther questions?More physical data to collect, ideally:Actual length, volume (MRI?)Same recordings with hand in various positionsOther?

AcksCobi Van Tonder: Photo/VideographyStacie V. Brink: Photography, Metrics, etc.Jose Luis Cruzado: Photo/Videography, Tech SupportCountryman Associates (Microphones)Meyer Sound Labs (Reference Test Speakers)OTHER/OTHER/OTHER/OTHER/OTHER

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

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