webapp/src/params.ts at 96aec9ccbd1f32e3cd77483a10eb12ef0dfb023c

simulated_instruments / triangle

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1// Parameter definitions for the triangle model, mirroring triangle_defaults.m.

2// Each parameter is assigned a tier that determines how much recomputation a

3// change requires:

4// solve -> FEM assembly + eigensolve + strikes + radiation + output

5// radiate -> strikes + radiation + output only (the cached mode basis is

6// reused; the eigensolve is the expensive part of this model)

7// output -> output stage only

8//

9// Note that the render duration is not a parameter: it is

10// (strike_count - 1) / strike_rate_hz + tail_s.

12export interface TriangleParams {

13 // Rod geometry

14 side_length_m: number;

15 gap_m: number;

16 rod_diameter_m: number;

17 // Rod material

18 density: number;

19 youngs_modulus: number;

20 poisson_ratio: number;

21 stiffness_trim: number;

22 // Discretization / mode retention

23 n_elements: number;

24 min_mode_hz: number;

25 max_mode_hz: number;

26 // Damping

27 loss_factor: number;

28 loss_slope: number;

29 radiation_loss: number;

30 // Beater

31 beater_radius_m: number;

32 beater_mass_kg: number;

33 beater_youngs: number;

34 restitution: number;

35 // Strike / roll gesture

36 strike_velocity: number;

37 strike_pos: number;

38 strike_angle_deg: number;

39 strike_count: number;

40 strike_rate_hz: number;

41 roll_pos2: number;

42 timing_jitter_ms: number;

43 velocity_spread: number;

44 seed: number;

45 // Radiation / listener

46 direct_gain: number;

47 listener_x_m: number;

48 listener_y_m: number;

49 listener_z_m: number;

50 speed_of_sound: number;

51 air_density: number;

52 // Rendering

53 sample_rate: number;

54 oversample: number;

55 tail_s: number;

56 pre_delay_ms: number;

57 normalize: boolean;

58 peak_dbfs: number;

59 full_scale_pa: number;

60 bit_depth: number;

61}

63export const DEFAULTS: TriangleParams = {

64 side_length_m: 0.152,

65 gap_m: 0.015,

66 rod_diameter_m: 0.008,

67 density: 7850.0,

68 youngs_modulus: 2.0e11,

69 poisson_ratio: 0.3,

70 stiffness_trim: 1.0,

71 n_elements: 60,

72 min_mode_hz: 20.0,

73 max_mode_hz: 22000.0,

74 loss_factor: 6.0e-5,

75 loss_slope: 4.0e-10,

76 radiation_loss: 1.0,

77 beater_radius_m: 0.0045,

78 beater_mass_kg: 0.022,

79 beater_youngs: 2.0e11,

80 restitution: 0.6,

81 strike_velocity: 1.5,

82 strike_pos: 0.17,

83 strike_angle_deg: 20.0,

84 strike_count: 1,

85 strike_rate_hz: 12.0,

86 roll_pos2: 0.4,

87 timing_jitter_ms: 6.0,

88 velocity_spread: 0.15,

89 seed: 1,

90 direct_gain: 1.0,

91 listener_x_m: 0.2,

92 listener_y_m: 0.1,

93 listener_z_m: 0.4,

94 speed_of_sound: 343.0,

95 air_density: 1.204,

96 sample_rate: 48000,

97 oversample: 2,

98 tail_s: 5.0,

99 pre_delay_ms: 3.0,

100 normalize: true,

101 peak_dbfs: -3.0,

102 full_scale_pa: 2.0,

103 bit_depth: 24,

104};

105

106export type Tier = 'solve' | 'radiate' | 'output';

107

108// Keys whose change invalidates the cached mode basis (the eigensolve). The

109// strike process, the listener, and everything downstream are deliberately

110// absent: striking somewhere else or moving the microphone reuses the modes.

111export const SOLVE_KEYS: (keyof TriangleParams)[] = [

112 'side_length_m', 'gap_m', 'rod_diameter_m',

113 'density', 'youngs_modulus', 'poisson_ratio', 'stiffness_trim',

114 'n_elements', 'min_mode_hz', 'max_mode_hz',

115 'loss_factor', 'loss_slope', 'radiation_loss',

116 'speed_of_sound', 'air_density',

117];

118

119export const RADIATE_KEYS: (keyof TriangleParams)[] = [

120 'beater_radius_m', 'beater_mass_kg', 'beater_youngs', 'restitution',

121 'strike_velocity', 'strike_pos', 'strike_angle_deg',

122 'strike_count', 'strike_rate_hz', 'roll_pos2',

123 'timing_jitter_ms', 'velocity_spread', 'seed',

124 'direct_gain', 'listener_x_m', 'listener_y_m', 'listener_z_m',

125 'sample_rate', 'tail_s',

126];

127

128export const OUTPUT_KEYS: (keyof TriangleParams)[] = [

129 'pre_delay_ms', 'normalize', 'peak_dbfs', 'full_scale_pa',

130];

131

132export interface ParamSpec {

133 key: keyof TriangleParams;

134 label: string;

135 unit?: string;

136 min: number;

137 max: number;

138 step?: number;

139 log?: boolean;

140 integer?: boolean;

141 help?: string;

142}

143

144export interface ParamGroup {

145 name: string;

146 specs: ParamSpec[];

147}

148

149export const PARAM_GROUPS: ParamGroup[] = [

150 {

151 name: 'Strike',

152 specs: [

153 { key: 'strike_velocity', label: 'Strike velocity', unit: 'm/s', min: 0.1, max: 6.0, step: 0.05, help: 'Beater speed at contact. Dynamics and timbre together: a faster strike gives a shorter Hertz contact and a brighter attack.' },

154 { key: 'strike_pos', label: 'Strike position', min: 0.01, max: 0.99, step: 0.005, help: 'Arclength fraction along the rod, 0 at the free end on the base. ~0.17 is the middle of the base; a node of a mode silences that mode.' },

155 { key: 'strike_angle_deg', label: 'Strike angle', unit: '°', min: 0, max: 90, step: 1, help: '0 strikes in the plane of the triangle, 90 normal to it. The two mode families are excited in this proportion.' },

156 ],

157 },

158 {

159 name: 'Roll',

160 specs: [

161 { key: 'strike_count', label: 'Strikes', min: 1, max: 64, step: 1, integer: true, help: '1 is a single strike; more gives a roll, the beater rattling in a corner.' },

162 { key: 'strike_rate_hz', label: 'Roll rate', unit: 'Hz', min: 2, max: 30, step: 0.5, help: 'Hits per second during a roll.' },

163 { key: 'roll_pos2', label: 'Second contact', min: 0.01, max: 0.99, step: 0.005, help: 'A roll alternates between the strike position and this one (the other leg of the corner).' },

164 { key: 'timing_jitter_ms', label: 'Timing jitter', unit: 'ms', min: 0, max: 20, step: 0.5, help: 'Gaussian jitter on each hit after the first. 0 sounds mechanical.' },

165 { key: 'velocity_spread', label: 'Velocity spread', min: 0, max: 0.6, step: 0.01, help: 'Lognormal spread of hit velocities during a roll.' },

166 { key: 'seed', label: 'Random seed', min: 1, max: 9999, step: 1, integer: true, help: 'Any change redraws the roll timing and velocities; the same seed always reproduces them.' },

167 ],

168 },

169 {

170 name: 'Beater',

171 specs: [

172 { key: 'beater_radius_m', label: 'Tip radius', unit: 'm', min: 0.001, max: 0.012, step: 0.0005, help: 'Radius of the beater tip; enters the Hertz contact stiffness.' },

173 { key: 'beater_mass_kg', label: 'Beater mass', unit: 'kg', min: 0.002, max: 0.12, log: true, help: 'A heavy beater lengthens the contact and darkens the strike; a light one brightens it.' },

174 { key: 'beater_youngs', label: 'Beater modulus', unit: 'Pa', min: 1e9, max: 4e11, log: true, help: 'Steel ~2e11. Lower it toward wood (~1e10) for a soft, dark contact.' },

175 { key: 'restitution', label: 'Restitution', min: 0.05, max: 0.95, step: 0.01, help: 'Coefficient of restitution; scales the momentum each strike transfers.' },

176 ],

177 },

178 {

179 name: 'Rod geometry',

180 specs: [

181 { key: 'side_length_m', label: 'Side length', unit: 'm', min: 0.08, max: 0.3, step: 0.001, help: '0.152 is a 6-inch triangle. Mode frequencies scale roughly as 1/L².' },

182 { key: 'gap_m', label: 'Corner gap', unit: 'm', min: 0.004, max: 0.05, step: 0.001, help: 'Arclength removed at the open corner. The opening is what frees the ends and detunes the near-degenerate pairs.' },

183 { key: 'rod_diameter_m', label: 'Rod diameter', unit: 'm', min: 0.004, max: 0.016, step: 0.0005, help: 'Bending frequencies scale as d; a thicker rod is also a louder radiator.' },

184 ],

185 },

186 {

187 name: 'Rod material',

188 specs: [

189 { key: 'density', label: 'Density', unit: 'kg/m³', min: 2000, max: 20000, log: true, help: 'Steel 7850, brass ~8500, aluminum 2700.' },

190 { key: 'youngs_modulus', label: "Young's modulus", unit: 'Pa', min: 5e10, max: 4e11, log: true, help: 'Steel 2e11. Frequencies scale as sqrt(E).' },

191 { key: 'poisson_ratio', label: 'Poisson ratio', min: 0.0, max: 0.45, step: 0.01, help: 'Sets the shear modulus and with it the torsional mode family.' },

192 { key: 'stiffness_trim', label: 'Stiffness trim', min: 0.4, max: 2.0, step: 0.01, help: 'Overall pitch trim for departures of a real triangle from the ideal geometry.' },

193 ],

194 },

195 {

196 name: 'Damping',

197 specs: [

198 { key: 'loss_factor', label: 'Loss factor η₀', min: 1e-6, max: 2e-3, log: true, help: 'Frequency-independent material loss. Steel is tiny, which is why a triangle rings for seconds.' },

199 { key: 'loss_slope', label: 'Loss slope η₁', unit: 's', min: 1e-11, max: 1e-8, log: true, help: 'Extra high-frequency damping; controls how fast the shimmer fades into the ring.' },

200 { key: 'radiation_loss', label: 'Radiation loss', min: 0.0, max: 3.0, step: 0.05, help: 'Scales the acoustic radiation damping estimated from the element dipole powers.' },

201 ],

202 },

203 {

204 name: 'Listener',

205 specs: [

206 { key: 'listener_x_m', label: 'Listener x', unit: 'm', min: -2.0, max: 2.0, step: 0.005, help: 'In the plane of the triangle. Radiation-only: no re-solve needed.' },

207 { key: 'listener_y_m', label: 'Listener y', unit: 'm', min: -2.0, max: 2.0, step: 0.005 },

208 { key: 'listener_z_m', label: 'Listener z', unit: 'm', min: -2.0, max: 2.0, step: 0.005, help: 'Normal to the plane: where the out-of-plane modes radiate best.' },

209 { key: 'direct_gain', label: 'Direct click gain', min: 0.0, max: 3.0, step: 0.05, help: 'Broadband local response at the contact, standing in for the truncated high modes. 0 leaves only the resolved modes.' },

210 ],

211 },

212 {

213 name: 'Output',

214 specs: [

215 { key: 'tail_s', label: 'Tail', unit: 's', min: 0.5, max: 12.0, step: 0.1, help: 'Ring time rendered after the last strike. A triangle needs seconds.' },

216 { key: 'pre_delay_ms', label: 'Pre-delay', unit: 'ms', min: 0, max: 50, step: 0.5 },

217 { key: 'peak_dbfs', label: 'Peak level', unit: 'dBFS', min: -24, max: 0, step: 0.5, help: 'Used when normalize is on.' },

218 { key: 'full_scale_pa', label: 'Full scale', unit: 'Pa', min: 0.1, max: 20, step: 0.1, help: 'Used when normalize is off: this many pascals maps to 0 dBFS.' },

219 ],

220 },

221 {

222 name: 'Advanced / quality',

223 specs: [

224 { key: 'n_elements', label: 'Elements', min: 24, max: 120, step: 1, integer: true, help: 'Finite elements along the rod. More converges the high modes; the eigensolve cost grows as its cube.' },

225 { key: 'min_mode_hz', label: 'Min mode freq', unit: 'Hz', min: 20, max: 500, step: 10 },

226 { key: 'max_mode_hz', label: 'Max mode freq', unit: 'Hz', min: 2000, max: 24000, step: 500 },

227 { key: 'oversample', label: 'Oversample', min: 1, max: 4, step: 1, integer: true, help: 'Synthesis rate multiple; 2 for render, 1 for preview.' },