Drum machine · qwen3.8-2.4t-a95b
Build a 16-step drum machine with a clickable grid for kick, snare, hi-hat, and clap, all sounds synthesized with the Web Audio API, plus play/stop and an adjustable BPM.
transcript · 14 messages
Build a 16-step drum machine with a clickable grid for kick, snare, hi-hat, and clap, all sounds synthesized with the Web Audio API, plus play/stop and an adjustable BPM.
thinking
Build a drum machine. Single file, sounds via Web Audio: kick (pitch-descending sine wave), snare (noise + tone), hi-hat (filtered noise), clap (noise burst). 16-step sequencer, play/stop, BPM slider, highlight the current step.
/tmp/ws/index.html (11501 bytes)Successfully wrote 11501 bytes to /tmp/ws/index.html
thinking
Noticed a bug I introduced myself: ` = audioCtx.createBuffer(1, len, audioCtx.sampleRate);` — the `noiseBuffer` declaration line is broken. Fixing it.
I spotted a typo in the noise buffer line — fixing it:
{"path":"/tmp/ws/index.html","edits":[{"oldText":" = audioCtx.createBuffer(1, len, audioCtx.sampleRate); const data = noiseBuffer.getChSuccessfully replaced 1 block(s) in /tmp/ws/index.html.
thinking
Let's check the syntax. I'll extract the JS and run a syntax check with node.
Let me verify the JS is syntactically valid:
{"command":"cd /tmp/ws && sed -n '/<script>/,/<\\/script>/p' index.html | sed '1d;$d' > /tmp/check.js && node --check /tmp/check.js && echo /tmp/check.js:27 noiseBuffer noiseBuffer = audioCtx.createBuffer(1, len, audioCtx.sampleRate); ^^^^^^^^^^^ SyntaxError: Unexpected identifier 'noiseBuffer' at wrapSafe (node:internal/modules/cjs/loader:1804:18) at checkSyntax (node:internal/main/check_syntax:76:3) Node.js v24.18.1 -rw-r--r--. 1 node node 11526 Aug 13 01:26 index.html
thinking
There was a duplicate "noiseBuffer" in the edit. I'll check the file.
{"path":"/tmp/ws/index.html","offset":186,"limit":8}const osc = audioCtx.createOscillator(); const gain = audioCtx.createGain(); osc.type = "sine"; osc.frequency.setValueAtTime(150, time); osc.frequency.exponentialRampToValueAtTime(40, time + 0.12); gain.gain.setValueAtTime(1.0, time); gain.gain.exponentialRampToValueAtTime(0.001, time + 0.4); osc.connect(gain).connect(audioCtx.destination); [196 more lines in file. Use offset=194 to continue.]
thinking
The oldText in my edit was ` = audioCtx.createBuffer(...)`, but the original line started with `noiseBuffer` — actually, the original file already had `noiseBuffer` written at the beginning of the line (it seems that during the write, "noiseBuffer" got dropped and it became ` = audio...`, but the error is showing a duplicate `noiseBuffer noiseBuffer`). Wait, the check is showing `noiseBuffer noiseBuffer = ...`. So does the original file have `noiseBuffer\n = ...`? Actually, my write already contained a truncated line, and the edit matched " = audioCtx..." which existed after "noiseBuffer". Therefore, currently that line reads `noiseBuffer noiseBuffer = ...`. Let me find it and fix it.
{"path":"/tmp/ws/index.html","edits":[{"oldText":"noiseBuffer noiseBuffer = audioCtx.createBuffer","newText":"noiseBuffer = audioCtx.crSuccessfully replaced 1 block(s) in /tmp/ws/index.html.
thinking
Wait — the original line: let me verify what that line looked like. The error indicated that there were 2 instances of `noiseBuffer` in the original text. In my initial `write`, I accidentally output `\n = audioCtx.createBuffer...` with a leading space, and before that... Actually, the `write` content I sent had ` = audioCtx.createBuffer(1, len, audioCtx.sampleRate); const data...` — hmm, it seems the content was garbled at that point. Well, whatever, it should be fixed now.
{"command":"cd /tmp/ws && sed -n '/<script>/,/<\\/script>/p' index.html | sed '1d;$d' > /tmp/check.js && node --check /tmp/check.js && echo JS OK -rw-r--r--. 1 node node 11509 Aug 13 01:26 index.html
thinking
JS syntax is OK. Let's also do a sanity check on the HTML (grep for tag pairs, and count the number of grid columns being built in JS — the grid is dynamically generated by JS, so that's fine). Done.
Done. `index.html` is a single self-contained file at `/tmp/ws/index.html` with no external resources, and its JavaScript passes a syntax check. **Features:** - **16-step grid × 4 tracks** (Kick, Snare, Hi-Hat, Clap) — click cells to toggle steps; activating a cell also auditions its sound instantly - **Fully synthesized Web Audio sounds:** - *Kick*: sine wave with exponential pitch drop (150→40 Hz) - *Snare*: high-passed white-noise burst + triangle-wave body - *Hi-hat*: short high-passed (7 kHz) noise tick - *Clap*: 4 staggered band-passed noise bursts - **Play/Stop button** (spacebar works too) using a **lookahead scheduler** — `setTimeout` schedules audio samples precisely against the AudioContext clock, while `requestAnimationFrame` syncs the visual playhead, so timing stays rock-solid - **BPM slider** (60–200, live-updating) with a numeric readout - Comes preloaded with a default groove so it sounds good immediately; beat-grouped cell shading, glowing active steps, and a white playhead outline; clicking a track name auditions that instrument
TAKE IT TO CODE
A single self-contained HTML file — copy it and open in any browser, or reuse the prompt with your own pi-agent run.
RUN
EVALUATION
16-step drum machine grid with kick/snare/hi-hat/clap, play/stop toggles, BPM slider, click programs steps and playhead advances.
Vision grade · anthropic/claude-sonnet-5
MEASUREMENTS
Raw readings from the capture, not a verdict — the grade above is the only judgement. Percentages are how much of the screen changed; the measure under-reports sparse motion on a dark background.