midiviz

Violinist biomechanics: what a standing, full-body rig needs

Research brief for the #037 violinist (18 Oct 2026): a MakeHuman man (default 163-bone rig, 180 cm) stands on a concert stage and plays the solo part of a MIDI file. Fingering, left-hand and bow motion and bowing physics exist for a floating violin (#033 / #034); this note covers the body that holds the instrument, the arms that reach it and the motion of the whole player. It does not repeat strings/research/01_violinist_rules.md, 02_algorithms.md (shifting data, bowing physics, score/audio → motion papers) or 03_violin_sound.md.

Tags: [V] checked in a source fetched for this brief; [T] teaching practice or observation, no measurement found; [calc] derived here. Body frame: x right, y up, z forward, origin on the floor between the heels unless stated. MakeHuman .L is the player’s left (−x).

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0. What the existing code gives us

strings/motion.js buildMotion(notes).poseAt(t) returns, per frame:

Field	Meaning	Use in the body rig
base, anchorU	hand position (semitones, cm from the nut, vibrato included)	left hand frame along the neck
thumb	thumb position flag (cello / bass)	– (violin: thumb rule §3.3)
vib	vibrato offset (cm, ±0.22 at 5.6 Hz, starts 0.15 s in)	wrist / forearm oscillation §3.5
fingers[1..4]	{ s, u, press, lift, held }	fingertip IK targets (hand3d.js, #029 solver)
bow	{ pos (cm from the frog, 0–65), dir, lift 0–1, speed cm/s, s (float string, 0 = G … 3 = E), playing }	bow pose → right hand frame §4

strings/sound/performance.js adds per-string curves at 250 Hz: bow velocity (m/s, signed), force (N) and β (bow–bridge distance / vibrating length).

strings/violin3d.js frame (cm): x along the strings (nut 0, bridge L = 32.8, body top x0 = 13.0, end button 48.6, scroll at −x, total ≈ 59 cm), y = top-plate normal, z across (G at +z). bowContact(s, β) gives the contact point; bowTilt(s) = lerp(−0.3, 0.3) rad, 34° G→E, about half the measured 65° (§4.3). hand3d.js has twoBone(A, C, l1, l2, pole), the left hand and a bow hold carried by the bow (thumb x ≈ 0.8, index ≈ 2.9, little finger ≈ −3.6 cm from the hair’s frog end). In #033 the shoulders are fixed points in the violin frame; in #037 the body places the violin. pianist/rig.js already poses this skeleton, measures UPPER, FORE, clavLen at load and spreads twist over upperarm01/02, lowerarm01/02: reuse it.

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1. Standing posture and whole-body motion

1.1 Stance [T]

• Feet about hip width apart: heels 20–30 cm, toes turned out 10–20°. Most players put the left foot slightly forward (5–15 cm) and the weight a little more on it, 55–60 % left at rest.
• Knees unlocked, 3–8° flexion; weight shifts start there.
• Pelvis level, the body turned 10–20° left of the audience direction so the violin (another 30–45° left of the chest) aims at the hall.
• Spine upright; the thorax turns another 5–10° left against the pelvis and tilts 2–5° left under the instrument’s weight.
• Sitting changes the right arm on the low strings only: standing gives more right glenohumeral abduction (max 47–74° vs 41–65° sitting) and less elbow flexion (max 95–112° vs 100–113°); 7 professionals, 240 Hz Qualisys [V, Roy et al. 2026].

1.2 How a violinist moves with the music

What the data say:

• In 12 professionals, the lumbar and thoracic spine, thorax, neck and left arm were “quite static”, and almost all motion was in the right arm [V, Wolf et al. 2019]. Whole-body motion is small and slow, but it is what makes the figure look alive.
• Experts move the bow-arm shoulder less in the sagittal plane than learners [V, Konczak et al. 2009].
• Sway carries leadership and emotion: a quartet leader’s sway predicts the others’ [V, Chang et al. 2017]; trio sway coupling rises in expressive takes [V, Chang et al. 2019]; a first violinist’s head moves more predictably in the quartet than solo [V, Glowinski et al. 2013].
• Violinists add motion and slow down at cadences, more at global than local resolutions [V, Chander et al. 2022]. Sway forms sinusoid-like and arch contours over phrases (trombonists) [V, Demos et al. 2017].
• No violin study with sway amplitudes in cm was found; the numbers below are estimates from concert video [T].

Suggested motion layers (amplitudes for “normal” expression; the expression slider scales them 0–2.5×) [T]:

Layer	What moves	Amplitude	Timing
Phrase sway	pelvis + chest translate left/right, weight shifts between the feet	±2–4 cm at the hips, ±3–6 cm at the head	one cycle per 1–2 phrases (4–8 bars); toward the right foot at phrase climaxes
Phrase lean	trunk pitches forward into a crescendo, back on a release	3–8°	follows the loudness curve, leading it by 0.2–0.4 s
Breath	inhale before phrase starts; shoulders and scroll rise	scroll +3–8°, shoulders +1 cm	0.3–0.6 s before the entry, exhale through the phrase
Cue	scroll lifts and drops on the downbeat (ensemble starts, after fermatas)	scroll 5–15° up, then down	lift one beat before, drop on the beat
Bow-driven trunk	chest turns left (toward the violin) and the right shoulder comes forward near the tip; turns back at the frog	2–5° yaw	in phase with long strokes (> 1 s); none for fast strokes
Violin meets bow	violin yaws a few degrees toward the bow on accents and long down-bows	2–4°	with the stroke
Knee bounce	knees flex on strong accents and chords	2–5°	on the accent, 0.1 s recovery
Head	nods on accents, turns slightly toward the scroll in high positions	2–6°	on beats; follows base

Keep two rules: sway is low-pass (no component faster than ~1.5 Hz except the knee bounce), and the violin is carried by the chest, so every trunk motion moves the instrument too (§2.4).

1.3 Three concert situations [T]

• Soloist with orchestra. At the conductor’s left, front edge, turned 15–30° toward the baton. In tuttis the violin comes down (by the neck at the left side or under the right arm, bow hanging), head toward the orchestra; re-raise 1.5–3 bars before the entry (lift ≈ 1 s, settle the jaw, bow on the string 0.3 s before the note). The orchestra carries the beat, so sway is free and largest at climaxes and cadenzas.
• Solo Bach. Nobody to cue: more centred, slower sway tied to harmonic rhythm, half the phrase sway, but stronger gestures on 3–4 note chords (arm sweep, small knee dip); head often still, eyes closed.
• Sonata with pianist. In the curve of the piano, turned 20–40° toward the pianist. Entrances cued with breath and scroll; both sway in phase on shared phrases (Chang et al.). During piano solos the bow comes off the string, the violin often stays up.

1.4 What anime exaggerates

• Your Lie in April (Kaori Miyazono). The director found violin far harder than piano (left hand and bow must be timed together). The studio filmed a model performer as reference, laid the violin out with 3D renders, drew most shots from above, and redrew fast passages with bigger, slower bow strokes because the real ones were too fast and small to read [V, Ishiguro 2015]. Kaori is written as free-spirited and improvising [V, fandom wiki]; on screen this comes out as large trunk leans, back-bends with the scroll up at climaxes, travelling steps, hair and dress in motion, eyes closed, and the bow flung off the string after final notes [T: general description, not checked shot by shot for this brief].
• Nodame Cantabile. Mine Ryutaro is a rock-minded violinist whose technique others call sloppy; in his exam performance, with Chiaki at the piano, he plays the violin part “in a metro and pop way” [V, fandom / MAL character pages]. For the rig that means hip swings, knee bends, head nods on the beat and wide bow flourishes [T]. Chiaki Shinichi, “a perfectionist gifted at both the piano and violin” [V, Rolling Stone India], is the opposite: upright, little sway, clean straight bowing.

Rig takeaways: an expression slider (§1.2 layers × 0–2.5) and an anime switch: visual bow strokes 1.5–2× longer at a lower rate in fast passages (sound unchanged), back-bends to 15–20° at climaxes, off-string bow flourishes at phrase ends, and a beat-locked “rock” style for Mine. Never exaggerate the left hand: viewers check the fingers.

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2. Holding the violin

2.1 Contact points [T unless marked]

• Lower bout on the left collarbone, the end button against the left side of the neck, 3–7 cm left of the suprasternal notch; a shoulder rest raises the back 2–5 cm and adds a contact on the front of the left shoulder.
• Jaw (left mandible, not the chin point) on the chin rest, over the tailpiece on the G side. The head’s weight, neck relaxed, stabilises the violin on the collarbone [V, violinist.com]. Rib 3.1 + arch 1.5 + chin rest 1.5–3 + shoulder rest 2–5 cm fill the 10–13 cm collarbone-to-jaw gap.
• Left hand at the index base and the thumb; it supports, the violin can be held briefly with no hand [V, The Strad].

2.2 Orientation, with numbers

Define the violin’s long axis (end button → scroll) and its lateral axis (across the top plate, G side → E side).

Angle	Range	Default	Source
Yaw: long axis vs the player’s facing direction, to the left	20–50° (standardised test positions); “approximately 45°+” in beginner checklists	40°	[V, Margulies et al. 2023; IUP checklist]
Roll: lateral axis vs horizontal, E side down	20–50°	30°	[V, Margulies et al. 2023]
Elevation of the scroll (pitch)	scroll between breast height (“low”) and shoulder height (“high”), ≈ −15° to +10°	+3°	[V, Frontiers 2026 playing types; calc]

Going from yaw 20° / roll 20° to 50° / 50° reduced the left upper arm’s adduction from vertical from 24.8 ± 2.7° to 18.6 ± 3.1°, left-shoulder elevation from 22.5 to 4.8 mm and protraction from 5.7 to 1.9 mm (30 students, 200 Hz mocap); low passive supination, high positions and the little finger increased these compensations [V, Margulies et al. 2023]. A second study found four playing types: scroll at shoulder or breast level, ≈ 20° or 45° to the frontal plane [V, Frontiers 2026]. Yaw 40° / roll 30° is a mid-range player; a flat, forward violin (20° / 20°) forces a raised, pulled-in left arm. The roll lets the bow arm reach the G string without lifting the elbow above the shoulder; from the audience the top plate faces up and to the player’s right.

2.3 Head [T]

• Rotation left 20–40°, lateral bend left 10–20°, flexion 10–20°; eyes down the fingerboard. Students with neck pain bend and rotate further left [V, Park et al. 2012, no numbers in the abstract]; use the low ends.
• Spread over neck01..03, head ≈ 20 / 25 / 25 / 30 %. The head may float off the chin rest in rests and low positions and presses more on down-shifts; nods ride on top.

2.4 How the violin moves with the body

• Attach the violin to a chest frame (spine01 orientation, left clavicle head position), plus its own small motion: breath and cue lifts, the bow-meeting yaw (§1.2), 1–2° wobble on heavy strokes; in total ±5° yaw, ±5° pitch, ±3° roll relative to the chest [T]. Scroll travel over a phrase is 5–15 cm, mostly from the trunk [T].
• The head follows the violin (solved after it), so the jaw stays on the chin rest.

2.5 Viola

• Body 38–43 cm vs 35.6, string length 36–38.5 cm vs 32.8, 25–35 % heavier [T; fingering.js L = 375 mm, violin3d.js scale ≈ 1.14]. Same hold, with more left-arm extension, the left elbow further right, yaw ≈ 45° [T]. Larger bow tilt (to 60° vs 45°) and higher force on the C string [V, Schoonderwaldt 2009]; bow ≈ 70 g.

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3. Left arm and hand

3.1 Arm posture in first position

For the default hold (§6.2) the hand at the nut is ≈ 45 cm forward-left of the left shoulder [calc]:

• Shoulder flexed ≈ 45–60°, horizontally adducted 30–45°, externally rotated so the forearm comes up under the neck [calc]; adduction from vertical 19–25°, elevation 5–23 mm [V, Margulies 2023].
• Elbow flexed ≈ 85–110° (interior 70–95°; ≈ 90° for the defaults, §6.4), more in high positions where the hand comes closer. It hangs under the neck, 25–30 cm below the strings.
• Forearm supinated 70–90°, near its limit [T]; less supination range means more shoulder compensation [V, Margulies 2023].
• Wrist straight in 1st position; the palm does not touch the neck [T].

3.2 Elbow swing [T]

So that each string gets the same finger shape, the elbow swings right (toward the midline) 2–3 cm per string from E to G, and further right and forward 1–1.5 cm per position, reaching the midline around 7th position on the G string. G vs D string playing differs measurably in the left wrist [V, Wolf et al. 2019].

3.3 Hand, thumb and wrist by position [T]

Position	Index base	Thumb	Wrist / palm
½–1st	touches the neck at the index MCP (first knuckle), level with the fingerboard on the E side	opposite finger 1 (or between 1 and 2), contact at the thumb’s tip joint, tip above the fingerboard edge by 0.5–1.5 cm	straight
2nd–3rd	same, the hand slides as a unit	moves with the hand, still opposite 1–2	straight; in 3rd the heel of the palm touches the rib at the neck heel
4th	the palm rests against the upper rib	starts to sit in the curve of the neck heel	starts to bend forward over the body
5th–7th	the hand comes over the upper bout	under the neck at the heel, then slides along the edge of the body	flexed forward 20–45° so the knuckles go over the fingerboard; the elbow is further right
8th+	over the body	only the tip under the neck heel, or off it	maximal

hand3d.js already parks the thumb at the neck heel for high positions and keeps the knuckles beside the fingerboard on the top-string side.

3.4 Fingers [T]

• Rounded fingers landing near the tip (flatter pads for wide vibrato and on the G string). PIP flexes most, DIP ≈ 0.6–0.8 × PIP (solveFinger, #029), MCP 30–60°: more on the E string, less on the G string where the finger reaches across. The fourth finger is flatter; it extends rather than curls.
• Lifted fingers hover 3–8 mm (2–4 mm in fast passages); fingers stay down under higher notes on the same string. Both are already in motion.js.

3.5 Vibrato

• Rate 5.9 Hz mean, ±15.2 cents [V, Mellody & Wakefield 2000]; 5.63 ± 0.48 Hz (4.1–6.8) in another corpus [V, Lionello & Ramírez 2018]; faster by 0.32 Hz and wider in high registers than low, and wider at louder dynamics [V, Influences of dynamic level… 2008]. Our performance.js uses 5.8 Hz, 15–35 cents.
• Fingertip travel [calc]: d(stop)/d(cent) = L·ln2/1200·2^(−d/12) = 0.19 mm·2^(−d/12) on the violin, so ±15 cents is ±2.5 mm in 1st position and ±1.7 mm at the 9th semitone. The motion.js amplitude (±2.2 mm) is right. The visible motion of the hand is larger than the fingertip’s because the finger rolls: the knuckles move 1.5–3× as far.
• Kinds, often mixed (Szeryng: “a combination of finger, wrist and forearm”) [V, The Strad]: arm (forearm swings about the elbow, ±1–2°, wide; high positions, G string), wrist (flexion/extension ±5–10°, forearm still; 1st–4th position), finger (the finger’s joints move, the hand yields passively, Galamian [V, violinist.com]; narrow, short notes, pp) [T for the angles]. Keep vib on the fingertip and add the matching wrist or elbow oscillation: arm mode for base ≥ 5th position or the G string.

3.6 Shifting

Measured shifts take 0.29–0.46 s regardless of tempo; tall players initiate up-shifts with the wrist and down-shifts with the thumb [V, Visentin et al. 2015, see 02_algorithms.md §6.1]. For the body:

• The arm leads up-shifts: the elbow starts swinging right/forward 50–100 ms before the hand, on the same minimum-jerk profile motion.js uses for the hand; on down-shifts the thumb moves first and the elbow follows [T].

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4. Right arm and bow

4.1 Bow dimensions and the hold point

• Violin bow 74–75 cm, 58–62 g, balance point 25–27 cm from the button end [V, Corilon]; hair 638–649 mm [V, Birmingham collection], ribbon ≈ 10 mm; frog ≈ 4.5–5 × 2 cm with the screw button behind it, a leather thumb grip and 8–10 cm of winding just ahead [T]. Viola bow ≈ 74 cm, 70 g [T].
• Hand on the bow (bow frame: x along the hair from the frog, y to the stick): bent thumb under the stick at the frog’s front (x ≈ 0–1), opposite the middle finger; index on the stick at x ≈ 3–4, near its middle joint; ring finger over the frog’s eye; curved little finger on top at x ≈ −2…−4 [T]. hand3d.js matches this.

4.2 The three bow holds [T]

Hold	Index contact	Pronation (forearm, at the frog)	Wrist / elbow	Look
Franco-Belgian	between first and second joint; fingers moderately spaced	30–45°	medium-high wrist, elbow at the bow’s level	the default (most modern players)
Russian (Auer)	deeper, at or past the second joint; index pressing more	45–60°, more toward the tip	higher elbow and wrist; flatter, longer fingers	Heifetz, Milstein
Galamian	between the two; fingers closer, little finger high and curved	30–40°	the arm “level” rule (§4.3)	US conservatory standard

Default Franco-Belgian; expose pronation offset and index depth as style.

4.3 Arm levels per string

Inclination (choosing the string) spans ≈ 65° from G to E in the instrument frame; tilt (stick toward the fingerboard) −10…45° on the violin, more at the frog and at pp; skewness ±10° [V, Schoonderwaldt 2009]. In fast patterns the crossing leads the bow change by ~15° of phase [V, Schoonderwaldt & Altenmüller 2014]. In the world the frog end drops by roll + local inclination [calc; roll 30°, ±22–32° about the A–D middle]:

String	Bow’s frog end vs horizontal	Right elbow height (180 cm man, shoulder at 147 cm)	Upper arm abduction
G	≈ 0–10° down	≈ shoulder level −5 cm (≈ 140 cm)	60–75°
D	≈ 15–25° down	≈ 133 cm	50–60°
A	≈ 30–40° down	≈ 125 cm	40–50°
E	≈ 45–60° down	≈ 118 cm	30–40°

This matches the standing abduction maxima of 47–74° on the low strings [V, Roy et al. 2026] and the “arm level” teaching: upper arm, forearm and bow roughly in one plane, the elbow at the bow’s height for each string [T]. Slow crossings move the whole arm to the new level; fast ones (arpeggios, bariolage) use wrist and fingers with the arm parked at the middle level [T].

4.4 Frog to tip: who does what

• Lower half: the upper arm moves (shoulder horizontal abduction), the elbow angle changes little; at the frog it is flexed 95–110° [V, Roy 2026 maxima; calc].
• Middle: the “square”, upper arm and forearm ≈ 90°, hand, wrist and elbow at one level [T].
• Upper half: the forearm opens to 20–40° flexion at the tip, pronation and index pressure increase, and the right shoulder protracts a few cm [T; §6.4 shows the arm cannot reach otherwise].
• Bow changes: wrist and fingers absorb the reversal; at the frog the fingers give 1–2 cm of “finger stroke” before the new down-bow [T].
• Speed: in an accelerando the velocity profile flips abruptly from rectangular to sinusoidal (7 Hz strokes for the violinist, max 15 Hz), and at the fastest rates wrist and elbow go from anti-phase to in-phase [V, Rasamimanana et al. 2009]. Fast détaché is forearm and wrist only.

4.5 Keeping the bow parallel to the bridge

The hand must travel on a straight line perpendicular to the strings. The arm does it by combining shoulder horizontal abduction/adduction, shoulder flexion and elbow extension, with the forearm rotating. Real paths are not perfectly straight: rounded paths and crooked bowing at the tip are normal even in renowned players, and skewness is used on purpose to move the contact point [V, Schoonderwaldt 2009, after Hodgson]; 0 ± 5° with a slight inward drift at the tip looks right. In the rig the bow is placed first and the wrist target taken from its grip, so the bow enforces the line and two-bone IK with the swivel rule (§6.3) supplies the elbow.

4.6 Wrist, fingers and pronation along the bow [T]

Bow position	Wrist	Fingers	Forearm pronation (added to the hold’s base)	Tilt
frog (0–10 cm)	flexed 15–30°, slight radial deviation	most flexed, little finger carrying the bow’s weight	+0°	largest (20–45°)
middle (25–35 cm)	neutral	medium	+10–15°	medium (10–20°)
tip (55–65 cm)	neutral to extended 10°	straight, index pressing	+20–30°	small (0–10°)

Tilt also rises at pp and falls at ff [V, Schoonderwaldt 2009]. Drive it from performance.js force: tilt ≈ lerp(35°, 5°, force / 1.5 N) blended with the bow-position term.

4.7 Strokes [T unless marked]

Stroke	Where on the bow	Motion	Typical numbers
Legato / long notes	whole bow	whole arm as in §4.4	10–30 cm/s at mf; whole bow in 1–4 s
Détaché	middle or upper half	forearm + wrist, upper arm still	20–60 cm/s; 5–20 cm per note
Martelé	upper half	a “bite” (force 1.5–3 N, index pressure) then a fast stroke and a stop on the string	stroke 10–25 cm, stop 50–150 ms
Spiccato	lower middle, near the balance point (20–35 cm from the frog)	bow dropped and lifted by wrist + forearm in a shallow arc	6–12 Hz, lift 0.5–2 cm
Sautillé	balance point / middle	bow bounces by itself, wrist and fingers keep it going	8–14 Hz, lift < 0.5 cm
Collé	at the frog	fingers pinch the string and lift: a finger stroke, the arm still	1–3 cm stroke, then lift 1–2 cm
Ricochet	upper middle	thrown, bounces 2–6 times on one stroke	10–15 Hz bounces
Bow lift / retake	–	circular path: lift, carry back to the frog, set down	lift 3–10 cm, 0.2–0.5 s

Bow speed 5–100 cm/s, force 0.1–2 N, 3–4 N on accents [V, Schoonderwaldt 2009]. motion.js already computes strokes, lifts and retakes.

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5. Motion data and models we could use

Source	What	Size / rate	Licence / access	Use
MOSA (Huang et al., TASLP 2024)	34 body/instrument markers (Qualisys, Vicon), audio, semantic labels; piano and violin	742 performances, 23 musicians, > 30 h	CC BY 4.0 with a research-use clause; Zenodo access restricted (request) [V]	best validation source for sway, head and violin angles vs audio
SPD (Jin et al., SIGGRAPH / TOG 2024)	markerless, 23 views, audio; 3D body, hands, instrument and bow	120 pieces, 3.0 h, cello and violin	HF repo tagged Apache-2.0; request form on the project page [V]	hands + bow + violin pose together: validate hand/bow frames and the violin hold
SPD-GEN / ELGAR (SIGGRAPH 2025)	whole-body cello motion from audio, SMPL-X, contact losses	–	form; SMPL-X licence applies [V]	method reference (hand–string and bow–string contact losses)
SyncViolinist (Nishizawa et al. 2024)	Vicon 120 fps, 57 body + 20 finger markers, bowing/fingering labels	3.1 h, 61 pieces, 75 joints	e-mail request [V]	richest labelled violin mocap: bow direction ↔ arm and fingers. Their avatar hangs the violin on the neck joint aimed at the left thumb’s first joint, and the bow on the right ring finger [V]
VioDat / VioPose (Yoo et al. 2024)	12-camera Vicon at 100 Hz with hand markers, video 30 fps, audio	639 videos, 12 players of mixed skill	project page; licence not stated [V]	vibrato and left-hand micro-motion
TELMI (Volpe et al. 2017); QUARTET (Papiotis et al. 2016)	marker mocap of body, instrument and bow	2.4 h violin; 0.5 h quartet	TELMI follow-up “made freely available” [V]; licences not checked	bow-arm kinematics by skill; ensemble sway
Kao & Su, ACM MM 2020	audio → 3D 15-joint violinist skeleton; dataset with several violinists per piece	11 h, 14 pieces	GitHub (one fold of preprocessed features) [V]; licence not stated	baseline for a learned sway layer
Audio2BodyDynamics (Shlizerman et al., CVPR 2018)	MFCC → LSTM → 2D keypoints of internet recital videos (violin and piano)	3.6 h	CC BY-NC [V]; starter data only	historical; 2D, not usable as 3D reference
Human–computer duet (arXiv 2009.07816, 2020)	a virtual violinist that follows a live pianist, body motion generated from audio	–	paper	sonata-with-pianist behaviour

The measurement papers (Schoonderwaldt, Rasamimanana, Margulies, Wolf, Roy, Turner-Stokes & Reid, Konczak, Visentin) give numbers but no downloadable data. None of the datasets can drive the rig without retargeting (marker sets, SMPL-X or 15-joint skeletons, access by request or research-only terms). Two uses are practical: (1) validation of the hold angles, elbow heights per string and sway amplitudes against MOSA or SyncViolinist (kept outside the repo like PIG and TNUA); (2) later, a learned sway layer (loudness / phrase features → pelvis, chest, head offsets) trained on MOSA, with the arms kept procedural: no dataset has bow contact as precise as our motion model.

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6. Rig recipe

6.1 Body numbers for a 180 cm man [T: Drillis & Contini ratios via Winter; measure the built skeleton at load]

Landmark / segment	Value
Eye height	≈ 168 cm (0.936 H)
Chin / jaw angle	≈ 156 / 158 cm
Shoulder (acromion) height	≈ 147 cm (0.818 H)
Suprasternal notch	≈ 146 cm
Shoulder joints, apart	≈ 36–40 cm (MakeHuman upperarm01 heads ≈ 35 cm in the scaled pianist rig)
Clavicle	≈ 15 cm
Upper arm (shoulder–elbow)	0.186 H = 33.5 cm; MakeHuman joints sit inside the landmarks (the pianist rig scaled to 180 cm: 26 cm upper arm, 24 cm forearm), so measure the male build
Forearm (elbow–wrist)	≈ 26 cm (0.146 H)
Hand (wrist–middle fingertip)	≈ 19 cm (0.108 H)
Hip joint height	≈ 95 cm

The pianist’s rig measures UPPER, FORE and clavLen from the skeleton; do the same, and scale the violin by 1.0 (a full-size violin for a 180 cm man).

6.2 Default hold in the body frame [calc]

Origin at the suprasternal notch N = (0, 146, 0); x right, y up, z forward.

• End button E = N + (−5, +1, +4) cm (left of the notch, on the collarbone, slightly forward because of the shoulder rest).
• Long axis d (end button → scroll) = yaw 40° left, elevation +3°: d = (−sin 40°·cos 3°, sin 3°, cos 40°·cos 3°) = (−0.64, 0.05, 0.77). The violin frame’s +x points along −d (scroll at −x).
• Roll 30° about d with the E side (violin −z) down, so the top-plate normal leans toward +x (the player’s right).
• Resulting points: nut ≈ E + 48.6 d = (−36, +3.5, +41) from N (hand in 1st position); bridge ≈ E + 15.8 d = (−15, +1, +16); scroll ≈ E + 59 d ≈ (−43, +4, +49); strings ≈ 5–6 cm above the collarbone along the top normal.
• Head: left jaw on the chin rest point (violin frame x ≈ 44, y ≈ +5.5, z ≈ +4); rotation left 30°, lateral bend 15°, flexion 15° as the starting guess, then solved (§6.3, step 4).

6.3 Per-frame order

1. Drivers (pure functions of t): phrase position, loudness (performance.js), beat phase, cue/breath events (entries after ≥ 1 bar rest), expression and style.
2. Legs: feet locked; pelvis offset from sway and weight shift; two-bone IK upperleg → lowerleg → foot, knee pole ahead + 10° out, 3–8° flex plus accent bounce.
3. Spine: chest yaw/pitch/roll from §1.2 layers, spread over spine05…spine01 (10/15/20/25/30 % from the pelvis up), plus the constant 5–10° left turn and 2–5° left tilt.
4. Violin: pose = chest frame × default hold (§6.2) × violin-own motion (breath, cue, bow-meeting yaw, chord wobble). Then the head: aim so the jaw point lands on the chin rest (solve a 2-DOF yaw/roll with fixed nod, spread over neck01..03, head); clamp rotation to 45°, bend to 25°.
5. Left hand frame from poseAt(t): origin at the index MCP, placed at x = anchorU from the nut, beside the fingerboard on the E side, 0.5–1 cm below the string plane; orientation from the neck (palm toward −z of the violin frame, fingers across the strings), with wrist flexion from §3.3 by base. Fingers by the existing hand3d.js solver.
6. Left arm: clavicle elevated 3–6° and protracted 2–4° (more for a flat hold); two-bone IK upperarm01.L → lowerarm01.L → wrist.L to the wrist point implied by the hand frame; twist split 50/50 into upperarm01/02 and lowerarm01/02; supination into lowerarm02.L + wrist.L. Pole: a point P_L below the violin = (violin centre under the neck heel) − 30 cm × top normal, shifted toward +x (body midline) by 2.5 cm × (3 − s) for strings E→G and by 1.2 cm × (base − 2)/2 per position, and forward by 0.8 cm per position. Add vibrato as ±1–2° elbow swing (arm mode) or ±5–10° wrist flex (wrist mode).
7. Bow: from bow and performance.js: contact point C = bowContact(s, β·L); bow axis a = across the strings in the plane given by inclination θ(s) (≈ ±32° about the D–A midpoint, i.e. 21.7° per string) and skewness 0 ± 5°; tilt from §4.6; lift along the string-plane normal (lift × 1.6 cm, more for retakes); position the bow so the hair point pos lies at C. The frog end is on the E side (player’s right).
8. Right hand frame = bow frame × the grip transform (hand3d’s bow hold), then the frog-to-tip blend of wrist flexion, finger flexion and pronation (§4.6) applied as small rotations of the hand about the grip point, so the bow stays put and the wrist target moves.
9. Right arm: if |wrist − shoulder| > 0.97 (l₁ + l₂), first protract and raise the right clavicle (up to 15°, ≈ 4 cm at the shoulder) and turn the chest up to 5° left; then two-bone IK upperarm01.R → lowerarm01.R → wrist.R. Pole (swivel): the elbow lies in the arm-level plane, the plane through the shoulder that contains the bow axis a; inside it, below the shoulder–wrist line. Offset the elbow from that plane by −8…−12 cm (below) at the frog, −3 cm at the middle, 0…+2 cm at the tip; add +2 cm for the Russian hold. Pronation goes into lowerarm02.R and wrist.R.
10. Constraints pass (§6.5), then apply secondary motion (sleeves, hair).

Timing details already in motion.js stay as they are (finger before bow ≤ 50 ms, string crossing leading the bow change by ≈ 15° of phase, shifts on a minimum-jerk path). Add: the elbows use the same profiles with a 50–80 ms lead for shifts (left) and string levels (right).

6.4 Reach check for the defaults [calc]

With shoulders at (±19, 147, −1) cm in the floor frame, contact point C ≈ (−15, 152, 17), bow axis toward the frog side (0.77, −0.3, 0.56) normalised:

• Frog on the E string: wrist ≈ (−12, 152, 18), 37 cm from the right shoulder → elbow interior angle ≈ 82° (flexion ≈ 98°), inside the measured 95–112° maximum [V, Roy 2026]. The right hand is in front of the left chest near the chin: correct, but watch the collisions (§6.5).
• Tip: wrist ≈ 65–67 cm further along the axis ≈ (36, 132, 55), ≈ 59 cm from the shoulder, more than l₁ + l₂ ≈ 56 cm. A real player reaches it by protracting the shoulder and turning the trunk, which is why step 9 moves the clavicle first. Keep the elbow at 15–25° flexion at the tip; never solve to a straight arm.
• Left hand in 1st position: hand ≈ 45 cm from the left shoulder; elbow ≈ (−24, 122, 20), under the neck; interior angle ≈ 85–95°.

6.5 Pitfalls

• The bow must stay on the string. Solve the bow from the contact point first and the arm second. If the arm cannot reach, move the shoulder and chest (step 9), never the bow. The hair touches the string; the stick must not touch it (tilt), and the bow must not pass through the adjacent strings (inclination per string, not the current 34° total).
• The bow-arm elbow must not cross the body. Keep the right elbow at x ≥ +8 cm (right of the sternum) and z ≥ −10 cm (not behind the back plane); at the frog on the E string, the right hand and the bow’s frog come within 10–15 cm of the face: check the hand against the chin and the frog against the left hand’s forearm.
• The left elbow must not intersect the violin. Keep it ≥ 12 cm below the violin’s back plane and the forearm ≥ 1.5 cm from the back and lower bout; test a capsule (forearm radius ≈ 3.5 cm with the sleeve) against the instrument’s outline every frame. High positions on the G string are the worst case.
• IK flips: clamp reach to 0.97 (l₁ + l₂), low-pass the pole (50–100 ms), keep it on one side of the shoulder–wrist line.
• Candy-wrapper forearms: split pronation over lowerarm01/02 and wrist.
• Head after violin, or the chin rest slides off the jaw on every nod.
• Feet must not slide when the pelvis sways.
• Scale: violin3d.js k must match the hold and the reach.
• Bow tilt sign: stick toward the fingerboard (toward the scroll), and more at the frog, the opposite of cello and bass [V, Schoonderwaldt 2009, after Trendelenburg].

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7. References (fetched or checked 18 Oct 2026)

• Chander et al. 2022, violinists’ gesture and timing at cadences, Music Perception 39(3) (abstract): https://online.ucpress.edu/mp/article/39/3/268/119730/Violinists-Employ-More-Expressive-Gesture-and
• Chang, Livingstone, Bosnyak & Trainor 2017, body sway and leadership, PNAS: https://pnas.org/doi/full/10.1073/pnas.1617657114
• Chang, Kragness, Livingstone, Bosnyak & Trainor 2019, body sway and joint emotion, Sci Rep 9:205: https://www.nature.com/articles/s41598-018-36358-4
• Corilon bow listings (length, weight, balance point): https://www.corilon.com/us/violin-bows/french-violin-bow-claude-thomassin; Birmingham Conservatoire collection (hair 638–649 mm): https://www.bcu.ac.uk/conservatoire/research/hic/the-collection/string-bow/10-31
• Demos, Chaffin & Logan 2017, sway and musical structure, Musicae Scientiae: https://musiclab.uconn.edu/wp-content/uploads/sites/290/2018/01/2017-Demos-Chaffin-Logan-1.pdf
• ELGAR, SIGGRAPH 2025: https://arxiv.org/abs/2505.04203, https://github.com/Qzping/ELGAR
• Frontiers in Psychology 2026, four violin playing types (abstract): https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2026.1944291/full
• Glowinski et al. 2013, quartet vs solo head movement, Front Psychol 4:841: https://pubmed.ncbi.nlm.nih.gov/24312065/
• Huang et al. 2024, MOSA dataset, IEEE/ACM TASLP: https://github.com/yufenhuang/MOSA-Music-mOtion-and-Semantic-Annotation-dataset, https://zenodo.org/records/11393449
• Influences of dynamic level and pitch register on the vibrato rates and widths of violin and viola players 2008 (authors not checked): https://www.researchgate.net/publication/249808850
• Ishiguro 2015, Your Lie in April director interview: https://myanimelist.net/featured/97
• IUP String Project checkpoints: https://www.iup.edu/musictheatredance/community-outreach/string-project/students/checkpoints-for-home-practice-violin-and-viola.html
• Jin et al. 2024, SPD, ACM TOG 43(4): https://arxiv.org/abs/2405.04963, https://github.com/Yitongishere/string_performance, https://huggingface.co/datasets/shiyi098/string_performance_dataset-SPD
• Kao & Su 2020, music-to-body-movement, ACM MM: https://arxiv.org/abs/2009.08015, https://github.com/hsuankai/Temporally-Guided-Music-to-Body-Movement-Generation
• Konczak, Vander Velden & Jaeger 2009, freezing degrees of freedom, J Mot Behav: https://pubmed.ncbi.nlm.nih.gov/19366657/
• A human-computer duet system for music performance 2020: https://arxiv.org/abs/2009.07816
• Lionello & Ramírez 2018, vibrato modelling, SMC: https://zenodo.org/records/1422607/files/smc_2018_048.pdf
• Margulies et al. 2023, left-arm compensation vs violin position, Front Psychol 13:1017039: https://pmc.ncbi.nlm.nih.gov/articles/PMC9901209/
• Mellody & Wakefield 2000, violin vibrato, JASA: https://pubmed.ncbi.nlm.nih.gov/10641668/
• Nishizawa et al. 2024, SyncViolinist: https://arxiv.org/abs/2412.08343, https://github.com/Kakanat/SyncViolinist
• Nodame Cantabile: https://nodamecantabile.fandom.com/wiki/Ryutaro_Mine, https://myanimelist.net/character/1187/Ryuutarou_Mine, https://rollingstoneindia.com/nodame-cantabile-manga-anime-live-action-series-comparison/
• Park et al. 2012, neck motion in violin students, MPPA 27(4): https://pubmed.ncbi.nlm.nih.gov/23247874/
• Rasamimanana, Bernardin, Wanderley & Bevilacqua 2009, bow stroke frequencies: http://articles.ircam.fr/textes/Rasamimanana09a/index.pdf
• Roy, Naaim, Hoegy, Verdugo & Duprey 2026, standing vs sitting, Multidiscip Biomech J 3: https://mbj.episciences.org/en/articles/17942/download
• Schoonderwaldt 2009, Mechanics and acoustics of violin bowing, KTH thesis: https://www.speech.kth.se/publications/pdfs/schoonderwaldt_e.pdf
• Schoonderwaldt & Altenmüller 2014, fast bowing coordination, PLoS ONE: https://pdfs.semanticscholar.org/9737/882fc7835aec8ff7a157dc5bc0257fcf35a1.pdf
• Shlizerman et al. 2018, Audio to body dynamics, CVPR: http://openaccess.thecvf.com/content_cvpr_2018/papers/Shlizerman_Audio_to_Body_CVPR_2018_paper.pdf, https://github.com/facebookresearch/Audio2BodyDynamics
• The Strad, arm/wrist/finger vibrato: https://www.thestrad.com/featured-stories/developing-arm-wrist-and-finger-vibrato/1859.article; nine steps to vibrato: https://www.thestrad.com/playing-hub/nine-steps-to-mastering-violin-vibrato/6748.article
• Turner-Stokes & Reid 1999, bowing-arm 3D analysis, Clin Biomech: https://pubmed.ncbi.nlm.nih.gov/10521625/
• Violinist.com, holding the violin: https://www.violinist.com/violin/how-to-hold-a-violin/; vibrato types: http://www.violinist.com/blog/annarougeheifetz/20124/13396/
• Visentin, Li, Tardif & Shan 2015, shifting, PeerJ 3:e1299: https://pmc.ncbi.nlm.nih.gov/articles/PMC4636401/
• Volpe et al. 2017, TELMI: https://telmi.upf.edu/; skill-level follow-up: https://www.researchgate.net/publication/345481353
• Winter, Biomechanics and Motor Control of Human Movement (segment ratios after Drillis & Contini)
• Wolf, Möller, Ballenberger, Morisse & Zalpour 2019, upper-body kinematics of violinists, MPPA 34(4): https://pubmed.ncbi.nlm.nih.gov/31800669
• Yoo et al. 2024, VioPose / VioDat: https://arxiv.org/abs/2411.13607