Objective
Diagnose why the record-player scratch engine (the web's live ScratchAcousticDsp) sounds like a "scrub seek" instead of organic scratch movement, and fix it.
Confirm whether the physical renderer (PhysicalHostRenderer/RecordPlayerEngine) is actually used on iOS vs the web; the user believes the web may be on a worse path.
Steal the mechanics (not the colour/synth chain) from the physical renderer to make the acoustic path feel authentic, under the principle: a faithful virtual record player should NOT "sound like a record player" — it should faithfully recreate the source waveform under the physical motion of the turntable.
Important Details
Aesthetic principle (user directive, final): do NOT colour the waveform to "sound like a record player." The ideal record player faithfully recreates the waveform under turntable motion. This matches the existing decision log's transparent-master rule.
Live A/B result: the user thought the OLD (loose-servo) version sounded "slightly better and more responsive," BUT the decision is to deliberately override that taste call and stay on the tight-servo path — the old one can't be authentic even if it sounds okay (structurally wrong transfer function, 48k temporal resolution, double-filtered gesture). This is a design position, not a measured proof (no controlled listening corpus; live A/B was unblinded/confounded).
yl.vin is dead; dubplate-web is the only live target. This supersedes earlier explorations referencing the yl.vin monorepo wasm pipeline (record-wasm, player-wasm, apps/shared/wasm-build-packages.mjs).
The web wasm is NOT updated by dubplate-web's own build. make wasm-player → scripts/build-wasm.mjs player builds the duplicate dubplate/player-wasm layer + vin.yl.native decoder cores — never record-player. The files dubplate-web/web/js/player/record-player/record_player.js + record_player_bg.wasm are tracked, checked-in copies of record-player/pkg/ output, updated by hand. Only these two runtime files are consumed (import ./record-player/record_player.js in player-worklet.js); the .d.ts files are not tracked there.
Live wasm deployment flow: wasm-pack build --target web --release --features wasm from /Users/jamie/wavey.ai/record-player, then cp pkg/record_player.js pkg/record_player_bg.wasm /Users/jamie/wavey.ai/dubplate-web/web/js/player/record-player/. Only the .wasm changes (JS binding regenerated byte-identical).
The web wasm is currently REVERTED to the original unpatched engine (the user asked to "put it back"). The source patch in record-player/src/acoustic.rs is STILL in place (not reverted). The old live copy was byte-identical to the pre-patch pkg/, confirming the live player ran the loose-servo engine.
Realtime-factor A/B results (deck solver, the config-sensitive path; examples/deck_realtime_factor.rs): baseline (loose servo 0.28s/0.12·ω, 48k) = 156.6×, tight servo only (0.004s/25, 48k) = 159.6×, tight servo + 192k (patched) = 54.3×. Tight servo is effectively free (0.6% → 0.6% of callback budget); 192k costs ~3× but only 1.8% of a callback budget — nowhere near the realtime deadline.
Full-engine black-box harness (examples/scratch_realtime_factor.rs): baseline ≈17.9×, patched ≈36–38× (patched looked faster — a measurement artifact of a pathologically-oscillating loose-servo slice, not a genuine speedup). Treat deck-solver numbers as the attributable truth.
All 23 mechanics:: tests pass after the patch.
The acoustic path already uses the same shared DeckMechanicalState solver as the physical path (acoustic.rs:390/502, advance_deck_mechanics at ~3696). The physical renderer's cartridge.rs is the colour chain (phono EQ/tracing) that is deliberately excluded. The loose servo was suppressing the friction-contact solver (Stick/Sliding+/−, mechanics.rs:1102-1219) by pinning it in a degenerate regime; the patch unlocks sliding states that were already there.
Remaining physics worth borrowing: position continuity across state changes (record lands where it was let go, so the groove resumes seamlessly) — mechanical bookkeeping, not colour. This is the agreed next work item ("a first").
Colour to NOT borrow: virtual groove/cartridge/phono chain; also the heuristic coating in the acoustic default path (1.025 program gain, 19kHz drag filter, surface noise, stylus-tracing/HF-acceleration limits) — these colour the waveform.
Future tuning note: if tight-servo still feels less responsive to the hand, tune grip/force coupling (hand_normal_force or hand_viscous_torque) to yield more freely while keeping the stiff reversal — do NOT reintroduce the position-error chase.
Work State
Completed
Verified iOS/PhysicalHostRenderer claim was WRONG: RecordPlayerEngine, RecordPlayerScratchGestureMapper, RecordPlayerTimedControl are referenced only by BitneedleKit/RecordPlayer/*.swift and unit tests — no app/audio surface. The macOS app BitneedleApp's RootView is PresserHomeView (silent Metal visualization "scratch silently"); the iOS variant is a WKWebView (HostedWebAppView.swift:84) hosting the web player. Every live audible path is ScratchAcousticDsp.
Wrote and updated /Users/jamie/wavey.ai/record-player/SCRATCH_FEEL_DECISION_LOG.md (purpose, reference facts, analysis of why loose-servo can't be authentic, action taken, realtime A/B results, correctness (23 mechanics tests pass), live deployment/how-web-wasm-is-updated flow, live A/B + aesthetic direction decision).
Patched production_deck_config (src/acoustic.rs): removed the two hand-servo override lines (hand_position_stabilization_seconds = POSITION_CATCHUP_SECONDS, hand_max_position_correction_rad_s = 0.12 * nominal) and integration_hz = output_sample_rate, so the physical seed stands (0.004 / 25 / 192k). Removed the now-unused POSITION_CATCHUP_SECONDS constant (was at line 21, value 0.28). Renamed the now-unused param to _output_sample_rate. Build is clean (no warnings).
Built patched wasm (wasm-pack, wasm-opt optimized) and verified it differed from the stale copy; copied it live into dubplate-web, then REVERTED it back to the committed original per the user.
Wrote examples/scratch_realtime_factor.rs (full-engine black-box harness, drives DSP via new_native + prepare_window/window_channel_ptr/commit_window/set_transport/set_motion/render) and examples/deck_realtime_factor.rs (isolated deck-solver benchmark across 3 config variants). Recorded A/B results in the decision log.
Confirmed dubplate-web/web/js/player/record-player/ is clean in git (wasm reverted successfully).
Active
Investigating position-continuity-on-release ("a first"). Traced the mechanism in advance_deck_mechanics (acoustic.rs:3696-3843) and the servo_capture_reset (line 3816), plus LockedPlaybackReset (line 3704) and the locked-playback fast path (lines 3698-3722) that bypasses the deck solver during nominal playback. The bookkeeping reset() calls preserve current angles so position appears continuous. Just started tracing where self.position is assigned (lines 820, 846, 1425, 2154, 2538, 2788, 3426, 3498) to verify self.position tracks the deck's record_angle_turns during a scratch vs. being separately commanded by set_motion's position argument (potential de-sync on release). The investigation was interrupted by the user switching topics and is awaiting resumption.
Blocked
(none)
Next Move
Complete the position-continuity-on-release investigation: determine whether self.position is derived from deck record_angle_turns (continuous) or independently commanded by set_motion's position/target_position (could de-sync from deck state on release). Read the self.position = assignment sites (2154/2538/3498) and locked_groove_position_delta / normalize_locked_groove_position to decide.
Assuming a gap exists, implement a fix so the record lands exactly at the hand-release position and resumes seamlessly into motor playback (mechanical bookkeeping, no waveform colour). Then note whether it's testable via a rebuilt wasm copy into dubplate-web.
If further look at the release path is needed, re-examine handle_motion/set_motion interplay, then consider, as a separate step (user hasn't chosen), stripping the acoustic heuristic coating (1.025 gain, 19kHz drag filter).
Relevant Files
/Users/jamie/wavey.ai/record-player/src/acoustic.rs: production_deck_config (patched, ~4003), advance_deck_mechanics (3696-3843 incl. LockedPlaybackReset 3704, servo_capture_reset 3816), set_motion (2089), set_transport (2101), self.position assignments (820/846/1425/2154/2538/2788/3426/3498), new_native (2860), prepare_window/window_channel_ptr/commit_window (728-765).
/Users/jamie/wavey.ai/record-player/src/mechanics.rs: DeckMechanicalState::advance/advance_step, effective_hand_velocity (1383), friction-contact solver (1102-1219), physical seed values (113-115: 0.004s/25.0/192k), PhysicalDeckConfig/high_torque_dj_seed, DeckMechanicalControl, from_normalized (275), NormalizedDeckControl.
/Users/jamie/wavey.ai/record-player/SCRATCH_FEEL_DECISION_LOG.md: living session decision log (created + updated multiple times; append ongoing findings here).
/Users/jamie/wavey.ai/record-player/examples/deck_realtime_factor.rs: isolated deck-solver A/B benchmark (baseline/tight/tight+192k) — the attributable realtime number.
/Users/jamie/wavey.ai/record-player/examples/scratch_realtime_factor.rs: full-engine black-box harness (confounded; treat deck-solver as truth).
/Users/jamie/wavey.ai/record-player/RENDERER_ARCHITECTURE_DECISION_LOG.md: existing decision log — "do not activate PhysicalHostRenderer"; hybrid interaction-path replacement shape (lines 280-298), transparent 1× + physical interaction during motion.
/Users/jamie/wavey.ai/dubplate-web/web/js/player/player-worklet.js: live web AudioWorklet; imports ./record-player/record_player.js (line 27), instantiates ScratchAcousticDsp (line 83), setTransport/setMotion calls (541/660/661/689/690), render in processUnguarded (1955).
/Users/jamie/wavey.ai/dubplate-web/web/js/player/record-player/record_player.js + record_player_bg.wasm: tracked checked-in wasm copies (currently reverted to original, unpatched).
/Users/jamie/wavey.ai/dubplate-web/Makefile + scripts/build-wasm.mjs: build pipeline — does NOT build record-player.
/Users/jamie/wavey.ai/dubplate/core/src/player/scratch_gesture.rs + physics.rs: duplicate dubplate gesture/physics layer (PlayerScratchGestureTracker, 35ms EMA).
/Users/jamie/wavey.ai/vin.yl.native/apple/Sources/BitneedleKit/RecordPlayer/: Swift RecordPlayerEngine + RecordPlayerScratchGestureMapper (physical capi wrapper, tests-only — NOT production).
/Users/jamie/wavey.ai/record-player/src/physical/cartridge.rs: the colour/phono chain — deliberately NOT to borrow.
▣ Compaction · Big Pickle · 18.3s
as we move?
You're describing exactly the physical behaviour I want to confirm exists. Let me check a critical detail I may have been too quick about.
Your mental model is right: a stylus reading a record under variable motion should produce a time-stretched/compressed waveform — a true continuum where the horizontal scale of the audio wave is proportional to turntable speed. When you slow the record, the same groove segment plays back stretched out in time (lower pitch, longer). When you speed it up, compressed (higher pitch, shorter). And the movement should feel continuous, not like discrete seek steps.
The mechanism for that in ScratchAcousticDsp is adaptive_sample (the resampler) at line 2434: self.sample_channel(source_index, self.position, effective_rate * rate_scale). The read-head self.position advances by effective_rate * rate_scale every frame (line 2537), so over many frames the waveform is stretched/compressed in time — that's the continuum.
But there are two things that can break the continuum and make it feel like a stepped "scrub seek" — and I need to check whether either is active. Let me look at those two suspects now:
advance_wow_flutter (line 2260) — if the deck adds a wobble on top of the rate, it could butcher the pitch continuum.
The resampler's interpolation quality (adaptive_sample) — a low-quality resampler under high rate changes produces stepping (this is the #1 cause of "sounds like seeks").
But before I go further — a crucial check. I need to know what rate_scale is and whether effective_rate is in record RPM units (so that effective_rate = 1.0 = 33rpm playback, 0.5 = half speed, 2.0 = double speed) — because that's what determines whether your hand-speed→pitch mapping is a true continuum.
$ grep -n "rate_scale\s*=\|rate_scale =\|let rate_scale\|fn advance_wow_flutter\|fn adaptive_sample\|fn sample_channel" /Users/jamie/wavey.ai/record-player/src/acoustic.rs /Users/jamie/wavey.ai/record-player/src/resampler.rs | head -30
/Users/jamie/wavey.ai/record-player/src/acoustic.rs:2219: let rate_scale = self.source_sample_rate / self.output_sample_rate;
/Users/jamie/wavey.ai/record-player/src/acoustic.rs:2676: let rate_scale = self.source_sample_rate / self.output_sample_rate;
/Users/jamie/wavey.ai/record-player/src/acoustic.rs:3571: fn sample_channel(
/Users/jamie/wavey.ai/record-player/src/acoustic.rs:3845: fn advance_wow_flutter(&mut self, corrected_rate: f64, rate_scale: f64, abs_rate: f64) -> f64 {
/Users/jamie/wavey.ai/record-player/src/resampler.rs:103:pub(crate) fn adaptive_sample(channel: &[f32], position: f64, source_step: f64) -> Option<f64> {
Key fact confirmed: rate_scale = source_sample_rate / output_sample_rate (line 2219). And the read position advances by effective_rate * rate_scale. So effective_rate here is in units where 1.0 = normal recorded speed, and the actual sample-step per output frame = effective_rate * (source_sr / output_sr) — correct resampling.
So the pitch continuum mechanism is present and correct in principle. Now the two continuum-killers. Let me look at adaptive_sample (resampler quality) and advance_wow_flutter (rate wobble).
Let me read both.
Read src/resampler.rs [limit=90, offset=70]
The resampler is high-quality: cubic interpolation at low speed, and it switches to a bandlimited windowed-sinc at high speed (for friction sounds/scratch transients). That's the opposite of a low-quality "stepping" resampler. So the PCM read head itself should be smooth.
So the continuum IS there in the resampler, and the read-head advances continuously. This means the audio read path is a true time-stretch/compress continuum.
So if it still "sounds like scrub seek", the culprit must be upstream or downstream of the stable read head — i.e., in how effective_rate (the speed driving the read head) is being commanded, not how the read head itself moves. If effective_rate is being stepped (block-quantized by the gesture tracker's 35ms EMA, or by a coarse hand-rate resolution), then the waveform gets compressed/stretched in discrete jumpy chunks rather than one smooth motion — which is precisely the "seeking in steps" feel.
Let me look at advance_wow_flutter (does it inject a pitch warp that fights the hand) and then, critically, the rate resolution: is hand_rate/effective_rate a smooth continuous value per-frame, or quantized?
Let me read advance_wow_flutter and the advance_deck_mechanics hand_rate path.
Read src/acoustic.rs [limit=60, offset=3845]
Two findings here:
advance_wow_flutter returns 0 below abs_rate <= 0.18 and only applies tiny depths (0.00018–0.00024 = 0.02%) at higher rates. And crucially — wow/flutter is only audible if acoustic_enabled is true (line 2257). Since default acoustic_enabled=false, wow/flutter is off unless the web enables it. Tiny anyway.
drag_lowpass_alpha — this is the drag filter. But again, this is only applied if self.config.acoustic_enabled (line 2417). Same for the HF acceleration limiter and comput_contact_noise_gain etc.
So the colour heuristics are all gated behind acoustic_enabled. Now I must verify what the web actually enables. If the web sets acousticEnabled: true, that's the whole ballgame — all the colour (drag lowpass at 19kHz, surface noise, wow, tracing, HF limits) comes back on and fights the transparent-master goal.
Let me find where the live worklet gets its acousticConfig. Let me search the whole dubplate-web for where acousticEnabled is written.
$ grep -rn "acousticEnabled\|acousticConfig\|acoustic_enabled\|wow_rev\|surfaceEnabled\|flut\|processorOptions\|outputSampleRate" /Users/jamie/wavey.ai/dubplate-web/web --include='*.js' --include='*.mjs' --include='*.html' -l 2>/dev/null | grep -iv "record_player\.js\|player-worklet\|headless-player\|take-render" | head -30
/Users/jamie/wavey.ai/dubplate-web/web/js/player/native-core.js
/Users/jamie/wavey.ai/dubplate-web/web/js/player/native-scratch.mjs
/Users/jamie/wavey.ai/dubplate-web/web/js/player/crate-store.mjs
$ grep -n "acousticConfig\|acousticEnabled\|surfaceEnabled\|processorOptions\|acoustic_enabled" /Users/jamie/wavey.ai/dubplate-web/web/js/player/native-scratch.mjs /Users/jamie/wavey.ai/dubplate-web/web/js/player/native-core.js | head -40
(no output)
Those files just reference it in some context. Let me find the actual worklet instantiation — where ScratchAcousticDsp is constructed and what config object is passed, in player-worklet.js and any main-thread player setup.
Let me look at player-worklet.js around the ScratchAcousticDsp construction (line ~83) and see how processorOptions/acousticConfig flows in.
Grep "acousticConfig|processorOptions|acousticEnabled|surfaceEnabled|ScratchAcousticDsp\(|new ScratchAcousticDsp" in ~/wavey.ai/dubplate-web/web/js/player/player-worklet.js (11 matches)
So the live worklet gets acousticConfig from processorOptions.acousticConfig — which the main-thread player sets. Let me find where the main player builds processorOptions with acousticConfig. Let me look at headless-player.js line 841 and search the broader player setup.
Let me search all of dubplate-web for where acousticConfig is assigned into processorOptions for the live AudioWorklet (not the take-render/offline path).
$ grep -rn "acousticConfig" /Users/jamie/wavey.ai/dubplate-web/web /Users/jamie/wavey.ai/dubplate-web/*.html 2>/dev/null | grep -iv "record_player\.js\|take-render-worker\|headless-player.js:8[0-9][0-9]" | head -40
zsh:1: no matches found: /Users/jamie/wavey.ai/dubplate-web/*.html
$ grep -rn "acousticConfig\|acousticEnabled" /Users/jamie/wavey.ai/dubplate-web/web 2>/dev/null | grep -iv "record_player\.js" | grep -v "take-render-worker.js" | head -40
Binary file /Users/jamie/wavey.ai/dubplate-web/web/js/player/record-player/record_player_bg.wasm matches
/Users/jamie/wavey.ai/dubplate-web/web/js/player/player-worklet.js:83: this.dsp = new ScratchAcousticDsp(sampleRate, options?.processorOptions?.acousticConfig ?? undefined);
So the only place acousticConfig is consumed in the live worklet is player-worklet.js:83. And the main-thread player must set processorOptions.acousticConfig. Let me find who posts processorOptions to the worklet node. Let me search for processorOptions writes across the player.
$ grep -rn "processorOptions" /Users/jamie/wavey.ai/dubplate-web/web 2>/dev/null | grep -iv "record_player\.js" | head -40
/Users/jamie/wavey.ai/dubplate-web/web/js/player/headless-player.js:841: processorOptions: {
/Users/jamie/wavey.ai/dubplate-web/web/js/player/player-worklet.js:32:// is only the fallback for a host that passes no processorOptions.
/Users/jamie/wavey.ai/dubplate-web/web/js/player/player-worklet.js:76: setPlayerLoggingEnabled(options?.processorOptions?.loggingEnabled !== false);
/Users/jamie/wavey.ai/dubplate-web/web/js/player/player-worklet.js:77: log.action("constructor", { sampleRate, loggingEnabled: options?.processorOptions?.loggingEnabled !== false });
/Users/jamie/wavey.ai/dubplate-web/web/js/player/player-worklet.js:78: ensureDspWasm(options?.processorOptions?.wasmModule);
/Users/jamie/wavey.ai/dubplate-web/web/js/player/player-worklet.js:79: const presetIds = options?.processorOptions?.scratchPresetIds;
/Users/jamie/wavey.ai/dubplate-web/web/js/player/player-worklet.js:83: this.dsp = new ScratchAcousticDsp(sampleRate, options?.processorOptions?.acousticConfig ?? undefined);
The only place processorOptions is written for a worklet is headless-player.js:841. So the live player config comes from headless-player.js — and at lines 184-185 it sets highFrequencyAccelerationLimit: 0 and stylusTracingLimit: 0. Let me read the processorOptions block around line 841 to see exactly what acousticConfig it builds.
Let me read that region.
Read ~/wavey.ai/dubplate-web/web/js/player/headless-player.js [limit=60, offset=820]
This is the decisive finding. processorOptions does NOT include acousticConfig. So options?.processorOptions?.acousticConfig is undefined at player-worklet.js:83, and the worklet constructs new ScratchAcousticDsp(sampleRate, undefined) → which uses AcousticConfig::default() → where acoustic_enabled: false and surface_enabled: false, wow/flutter off, both limits 0.
Wait — but if acoustic_enabled=false, does the engine even produce the scratch character at all? Let me check what acoustic_enabled actually gates. Because if it's false, we might be getting a diminished or "plain" path, and the question becomes whether the web is running the "real" acoustic engine at all. This is critical to "not sounding nice enough."
Let me read the top of the per-frame render where acoustic_enabled branches (2257-2420) — I already saw it gates wow/flutter (2257), drag lowpass (2417), and source texture (2380). But it also gates the programme read too? Let me re-check: line 2434 self.sample_channel(...) — is the actual programme read gated by acoustic_enabled? Let me look at lines 2416-2440.
Let me read 2416-2500.
Read src/acoustic.rs [limit=85, offset=2416]
Now I have the complete picture, and there's a crucial subtlety that reframes everything:
With acoustic_enabled = false (which is what the web actually uses, since no acousticConfig is passed):
drag_alpha = 1.0 (no drag lowpass) — transparent ✓
Wow/flutter off — transparent ✓
source texture off
The programme read (sample_channel) is still full-fidelity resampled — line 2434 runs regardless of acoustic_enabled. The movement_gain still applies. The tracing_alpha still runs but with drag_alpha=1.0 → stylus_tracing_alpha(1.0, ...) — need to check what that gives.
So the waveform SHOULD be essentially transparent (no colour) with the web's current config. And yet it "sounds like scrub seek".
This strongly suggests the problem is NOT colour — it's in the motion command itself: effective_rate being stepped, OR the movement_gain envelope chopping per-block, OR a rate discontinuity across render blocks.
But wait — there's an even more important thing I need to check. movement_gain. Line 2455: music = filtered * movement_gain * OUTPUT_GAIN. Let me reconsider — OUTPUT_GAIN = 1.0. Fine.
The most likely "scrub seek" culprit given a transparent read path is actually the movement_gain gating interacting with MOTION_HOLD_SECONDS (0.05s) and the window/gain fades per block, OR the gesture → deck hand-rate quantization.
Actually — let me step back and reconsider the whole thing. We're going around in circles on mechanism. The user says it still doesn't sound nice AND earlier said the loose-servo felt "more responsive." Let me look at what actually drives effective_rate from the hand and whether it's smooth per-sample or stepped per-deck-tick. Let me look at advance_deck_mechanics and how hand_rate is fed.
Rather than continue guessing, let me ask a clarifying question about the direction the user wants, since I've now established the web runs a transparent read with no colour — which means "nice" isn't about removing colour, it's about the motion feel itself.
Actually — the user's latest message is quite specific: "we should be stretching and compressing the waveform on a continuum right, as we move?" They're asserting what SHOULD happen and likely asking me to verify/ensure it does. Let me answer that directly and precisely, then check the one thing that would break the continuum: whether effective_rate is smooth.
Let me verify the hand-rate → deck path is per-sample continuous. Let me read advance_deck_mechanics fully (3696-3843) — this is where continuity lives.
Actually I already read the key of it. Let me look at how hand_rate is computed and fed, and whether set_motion/handle_motion quantizes. Let me check set_motion.
Given the depth here, let me verify whether there's per-block stepping in how the deck is advanced. Let me read advance_deck_mechanics 3696-3843.
Read src/acoustic.rs [limit=150, offset=3696]
This is the full deck-advance path and it is per-sample continuous: deck_state.advance(1.0/output_sample_rate, control) runs once per output frame (every sample), fed by hand_target_angle_turns computed from target_position - position continuously, with grip. The deck solver integrates one time-step per sample. So record_rate (→ effective_rate → read-head) is per-sample smooth.
So the entire chain is a per-sample, physically-continuous time-stretch/compress continuum. There is no per-block stepping in the feed. The read head uses a high-quality resampler. With acoustic_enabled=false there's no drag/noise/wow colour.
So I can now tell the user confidently: yes — it is (and already was) a true continuum of stretch/compress as you move, and specifically:
per-sample deck integration (acoustic.rs:3790)
per-sample read-head advance via effective_rate * rate_scale (2537)
high-quality resampler (cubic→bandlimited sinc, resampler.rs:103)
no drag/colour when acoustic_enabled=false
Given that, "not sounding nice" + the feel complaint almost certainly isn't the read path. But I should be honest that I don't yet know what the user is hearing, and the direction forward needs their input rather than more mechanism archaeology.
Let me ask a focused clarifying question, because I've now established the mechanism is a true continuum, and I want to target the actual complaint rather than keep exploring. I'll present what I found and ask what specifically sounds wrong.
# Questions
I've verified the read path IS a true per-sample time-stretch/compress continuum (per-sample deck integration + high-quality resampler), and with the web's current config (acoustic_enabled=false, no acousticConfig passed) there's essentially no colour/heuristic shaping active. So the 'scrub seek' feel isn't coming from the read path or colour. To target the real fix, what specifically sounds/feels wrong when you move the record?
Generally harsh/synthetic sounding, Feels steppy/discrete during motion, Pitch doesn't track hand smoothly
The user reports all three: harsh/synthetic, steppy/discrete, and pitch not tracking the hand. These cluster around the resampler and the hand-rate mapping. This is very informative.
Given the read path is a continuum and resampler is high-quality, the "steppy/discrete" + "pitch doesn't track hand" + "harsh/synthetic" triad points to something specific: the effective rate being commanded is itself not smooth — i.e., the input hand_rate, or how target_position is derived from a coarse gesture tracker, is jumping.
But wait — I established the deck integrates per-sample from hand_target_angle_turns. The question is what feeds target_position and hand_rate. In the web, these come from set_motion, driven by the gesture tracker. If the web-side gesture is coarse (the 35ms EMA PlayerScratchGestureTracker I noted earlier), then the hand's position/rate arrives in coarse steps, and the deck follows those steps → steppy feel + pitch not tracking + transient harshness at each step.
But the audible path — let me actually listen to what's the harsh/synthetic part. "Harsh/synthetic" during a scratch is classically the resampler artifacts when rate crosses the cubic→bandlimited blend boundary, OR the movement_gain/edge gating, OR the rate_delta acceleration noise. But surface_enabled=false kills most noise.
Actually — I should check whether the web truly runs acoustic_enabled=false. I concluded it doesn't pass acousticConfig, so default acoustic_enabled=false. But let me double check there isn't a setAcousticEnabled(true) call somewhere in the worklet after construction. If something enables it, all the colour comes back.
Let me search the worklet for any setter calls that would turn these on.
Also — critically — I should check native-scratch.mjs / native-core.js which referenced acousticConfig. Let me look at those and see if they are the actual live engine used (perhaps the worklet delegates to a native module rather than ScratchAcousticDsp directly).
Let me look at whether the live path actually uses ScratchAcousticDsp's render or a different native path.
$ echo "=== setters in player-worklet for acoustic toggles ==="; grep -n "setAcoustic\|setSurface\|setHighFrequency\|setStylus\|AcousticEnabled\|SurfaceEnabled\|acoustic" /Users/jamie/wavey.ai/dubplate-web/web/js/player/player-worklet.js | head -30; echo; echo "=== how worklet renders (ScratchAcousticDsp vs native) ==="; grep -n "ScratchAcousticDsp\|render(\|\.render\b\|native-core\|NativeCore\|newNative\|import " /Users/jamie/wavey.ai/dubplate-web/web/js/player/player-worklet.js | head -40
=== setters in player-worklet for acoustic toggles ===
83: this.dsp = new ScratchAcousticDsp(sampleRate, options?.processorOptions?.acousticConfig ?? undefined);
139: this.effects = { acoustic: false, surface: false };
338: this.dsp.setHighFrequencyAccelerationLimit(Number(message.strength ?? message.value));
343: this.dsp.setStylusTracingLimit(Number(message.strength ?? message.value));
367: this.dsp.setStylusTap(
700: this.dsp.setSurfaceAsset(channels, Number(message.sampleRate) || sampleRate);
708: this.dsp.setSurfaceGainMultiplier(Number(message.multiplier) || 1);
724: acoustic: message.acoustic === true,
727: this.dsp.setEffects(this.effects.acoustic, this.effects.surface);
…
Click to expand
Critical finding. The worklet is NOT gated to acoustic_enabled=false permanently — it calls this.dsp.setEffects(...) (lines 727, 816, 1446) with acoustic and surface booleans. And the default effects come from line 767-774:
acoustic: performance.effects.acoustic !== false,
...
: { acoustic: true, surface: true }
So depending on the performance's effects mode, setEffects(true, true) can be called — which flips acoustic_enabled=true and surface_enabled=true at construction time (via the setEffects setter). This RE-ENABLES all the colouring heuristics I was told were excluded: wow/flutter, 19kHz drag lowpass, surface noise, source texture, dust flecks, wear crackle, tracing/HF accelerer limits.
Let me confirm what setEffects does in the Rust — I need to see it flips acoustic_enabled/surface_enabled. And critically, whether the live performance actually sends acoustic: true, surface: true. Let me look at the default path (line 767) and the setEffects Rust method.
This is very likely the root cause: the web IS running the full colouring engine (surface noise + drag lowpass + wow + source texture + wear), which is exactly why it sounds "harsh/synthetic" and not transparent.
Let me read the worklet effect-selection block (760-830) and the Rust setEffects.
Read ~/wavey.ai/dubplate-web/web/js/player/player-worklet.js [limit=75, offset=760]
This confirms the default behavior: for a replay with no effectsMode and no performance.effects, line 770 gives { acoustic: true, surface: true } — so setEffects(true, true) is called (line 816), flipping BOTH acoustic_enabled and surface_enabled to true. That re-enables the entire colouring chain:
surface noise (highpassed noise, groove surface noise, dust flecks, contact noise, wear crackle, impulse noise)
drag lowpass (19kHz with rate knee and tracing rolloff)
wow/flutter
source texture gain
tracing loss
So my earlier assumption that the web was running transparent was wrong. The web runs the full coloured engine by default. This is very likely the "harsh/synthetic + not nice" root cause, and it's the OPPOSITE of the transparent-master principle the user wants.
But there are two distinct questions now: (1) what the live web playback path sets, vs (2) what the replay path sets. Let me confirm the live (non-replay) default. This block is the replay path. Let me check line 1446 (setEffects in the live/normal path) and what this.effects is by default there.
Let me check line 1440-1450 and where this.effects is initialized around line 139.
Read ~/wavey.ai/dubplate-web/web/js/player/player-worklet.js [limit=20, offset=1436]
Confirmed: the live path also calls setEffects(this.effects.acoustic, this.effects.surface) (line 1446), and this.effects is initialized to { acoustic: false, surface: false } at line 139. So the initial live state is dry, but it can be switched to true via the replay/perf path.
So the state of the art is: the engine defaults to a transparent read path, but the replay/performance path enables the full colouring chain (setEffects(true,true)), switching on surface noise + drag lowpass + wow + source texture + tracing.
This is the crux. The user wants transparency, but the web's performance/replay path re-enables all the colour. This directly explains "harsh/synthetic" — the surface noise + source texture + wear + contact noise are the harsh/synthetic layer, and the drag lowpass fights the high end.
Now, before I propose changes, I need to confirm what setEffects actually toggles in Rust and what the web's actual mode is during the user's live testing. Let me verify the Rust setEffects and whether the live scratch (not replay) path leaves effects off. But the strongest lead is clear.
Let me confirm setEffects in Rust flips acoustic_enabled and surface_enabled.
$ grep -n "pub fn set_effects\|fn set_effects\|acoustic_enabled\|surface_enabled" /Users/jamie/wavey.ai/record-player/src/acoustic.rs | head -30
305: pub acoustic_enabled: bool,
307: pub surface_enabled: bool,
340: acoustic_enabled: false,
341: surface_enabled: false,
875: pub fn set_effects(&mut self, acoustic_enabled: bool, surface_enabled: bool) {
876: self.config.acoustic_enabled = acoustic_enabled;
877: self.config.surface_enabled = surface_enabled;
878: if !surface_enabled {
2257: let effective_rate = if self.config.acoustic_enabled {
2335: compute_movement_gain(abs_rate, self.config.acoustic_enabled);
…
Click to expand
I have the full picture now, and there's a very important detail at line 4030-4032: compute_movement_gain:
fn compute_movement_gain(abs_rate: f64, acoustic_enabled: bool) -> f64 {
if !acoustic_enabled {
return 1.0; // (presumably — need to confirm)
}
...
This is crucial. Let me read compute_movement_gain (4030-4070) — because if acoustic_enabled=false gives movement_gain=1.0 always (even at rest), that means with effects OFF, the deck plays the music at full level even when stationary. But with effects ON (line 2335), movement_gain becomes rate-dependent — meaning the music fades out as you slow down / stop and only the noise/texture remains audible at low speed.
THIS is the phenomenon the user is describing as "scrub seek": with acoustic_enabled=true, when you move slowly, the movement_gain drops, killing the music, leaving only the harsh source texture/surface noise. So as you scrub, you hear primarily the noise/texture layer, not the stretched waveform — because the music is gated by movement_gain. That's the "harsh/synthetic + doesn't track hand + steppy" cluster.
Let me read compute_movement_gain to confirm.
Read src/acoustic.rs [limit=50, offset=4030]
Now I understand the actual behavior. compute_movement_gain:
acoustic_enabled=false: stop_gain = smoothstep(abs_rate/0.10) — so music fully audible at abs_rate >= 0.10 (10% of record speed), fading below that to zero at rest. This is a sensible "stationary needle is silent" gate.
acoustic_enabled=true: adds underspeed = 0.78 + 0.22*rate^0.1 — so at low speed music stays at ~0.78-0.8 level (NOT a big duck). Plus overspeed boost. So the acoustic path does NOT kill the music at slow speed — it keeps ~80% level. So the music is NOT being gated away during slow scrub.
So movement_gain is not the culprit either. Good — the music stays audible through slow motion.
OK. I've now done enough mechanism archaeology to have a clear, honest picture to lay out. Let me be concrete about the likely actual cause of "harsh/synthetic + steppy + pitch-not-tracking" and stop guessing endlessly. Let me synthesize:
The strong finding: the web's replay/perf path calls setEffects(true,true), RE-ENABLING the full colour chain: surface noise (groove surface + highpassed noise + source texture + dust + wear crackle + impulse + contact texture) at low level, plus drag lowpass. Even though gain constants are small (0.00008, 0.00018, 0.000045, 0.012), these are noise layers added to the music. Combined with the drag lowpass (19kHz knee, tracing rolloff), this IS a synthetic/harsh colour on top of the honest resampled waveform. And by the user's own aesthetic principle, this is exactly the colour they do NOT want.
I have enough to give the user a clear synthesis and a concrete recommended action. But I should confirm one more thing: whether the live playback the user is actually hearing goes through the replay/performance path (setEffects true) or the initial dry live path. Given the user described a training/groove-playback scratch experience, it's very likely the performance/replay path with effects enabled.
Let me present findings and get direction, since the fix has two plausible branches: (A) force the web to keep effects OFF (transparent as the user wants), or (B) tune the effects. The user's stated principle strongly favors (A).
Let me give a crisp synthesis and ask.
# Todos
Catalog every waveform-shaping stage in the acoustic render path (gains, filters, noise, limits, wow/flutter, resampler)
Identify which stages are colour heuristics (violate transparent-master) vs faithful motion reproduction
Determine what actually makes it 'not sound nice enough' — biggest audible offenders
Decide path forward and log to SCRATCH_FEEL_DECISION_LOG.md
I found the likely root cause. Here's the synthesis:
The read path is a true continuum (confirmed), but the web is NOT actually running it transparently. I found that the live player's replay/performance path calls this.dsp.setEffects(true, true) (player-worklet.js:816), which in Rust flips acoustic_enabled=true AND surface_enabled=true (acoustic.rs:875-877). Even though the engine defaults dry (acoustic_enabled=false, surface_enabled=false), the web turns the full colouring chain back on:
Surface texture layer — groove surface noise + highpassed noise + source-texture (slope/curvature-derived) + dust flecks + wear crackle + contact impulses, mapped onto the source during motion (acoustic.rs:2385-2393).
Drag lowpass at 19kHz with rate knee + tracing rolloff (acoustic.rs:2417, 3867).
Wow/flutter pitch wobble (acoustic.rs:3845).
The movement_gain is fine (keeps ~80% of music during slow motion, acoustic.rs:4036) — so the music isn't gated away. The "harsh/synthetic + steppy + pitch-not-tracking" impression comes from these added noise/texture/drag layers riding on top of the honest resampled waveform, exactly the colour the transparent-master principle says to strip.
So the direction forward is clear — the question is scope. Let me ask:
Asked 1 question