Studio Bongos

Circular membrane physics · Bessel function modal synthesis · Kill-on-retrigger

Instrument Summary

Circular membrane percussion using the physically correct Bessel function frequency ratios. A struck circular membrane vibrates at frequencies determined by the zeros of Bessel functions J₀ and J₁ — not harmonic multiples. Six modes are synthesised with per-mode amplitude and physically correct decay times. Strike position determines which modes are excited.

Synthesis Features

  • Membrane modal ratios: [1.000, 1.593, 2.136, 2.296, 2.653, 2.917] from Bessel zeros
  • Per-mode decay: τₙ = τ₁ × [1.0, 0.55, 0.35, 0.28, 0.18, 0.12]
  • Strike position: centre hits symmetric modes (J₀), edge hits asymmetric (J₁)
  • Kill-on-retrigger: activeVoices dict prevents voice stacking
  • Rim shot: fires at 4.8×(high) or 3.9×(low) fundamental when striking outer 28%
  • Head noise: bandpass-filtered noise (open=1600Hz, slap=2800Hz, mute=1000Hz)
  • Shell EQ: peaking filter at 900Hz(high)/620Hz(low), Q=1.4
  • 3 articulations: Open, Mute, Slap — each changes decay, noise character, amplitude

Signal Chain

6 modal oscillators + head noise → Shell EQ → Output gain (ADSR) → Master

Academic References

1968Morse, P.M. & Ingard, K.U. Theoretical Acoustics. Princeton University Press. Chapter 9. — Circular membrane vibration modes. The Bessel function zeros giving ratios 1.0, 1.593, 2.136, 2.296, 2.653, 2.917 are from Table 9.3.
2000Rossing, T.D. Science of Percussion Instruments. World Scientific. Chapter 3. — Bongo and conga acoustic measurements. Strike position effects on mode amplitudes. The center vs. edge amplitude profiles used in MODAL_AMPS_CENTER and MODAL_AMPS_EDGE.
2002Avanzini, F. & Rocchesso, D. "Controlling material properties in physical models of sounding objects." ICMC Proceedings. — Modal synthesis architecture for struck membranes. Inspired the per-mode GainNode with independent exponential decay implementation.

Studio Bongos

Hand percussion synthesis · low & high drums · open, mute, slap articulation

Connected MIDI via Instrudio App
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2.2k
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Tap drum center for warm open tones · edge for brighter slap accents
Hembra · Low
Macho · High
Center hitRounder tone with more body resonance and longer bloom.
Edge hitSharper attack with brighter ring and more transient energy.
Suite autoplayClassical score melodies are mapped into expressive low/high bongo phrases automatically.
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