[Roadmap] Audio polish

[Otaiki1]

Overview

A second-pass audio design pass after the base audio integration ships. Goal: a cohesive, cinematic audio layer tightly coupled to the visual escalation system.

Status: Post-MiniPay launch roadmap. Depends on Audio integration issue #9.

Improvements

Dynamic music system

• Three intensity layers: ambient (sparse) → active (driving beat) → intense (max BPM + percussion)
• Layers crossfade based on current score tier (Tier 0 = ambient, Tier 2 = active, Tier 3+ = intense)
• Implemented via Web Audio API AudioBufferSourceNode with crossfade gain nodes

Positional audio

• Piece placement pitch varies by column (left = lower, right = higher) — creates a xylophone effect
• Line clear pans from the direction of the cleared row/col (left pan for vertical clears, stereo for horizontal)

Haptic + audio sync (MiniPay)

• Every navigator.vibrate() call gets a matching audio cue at the same frame
• Short vibration = short click SFX; long vibration = longer swoosh SFX

Combo crescendo

• Pitch of the clear sound rises one semitone per streak level
• At UNSTOPPABLE tier: +7 semitones above base pitch
• Implemented via AudioBufferSourceNode.playbackRate (1.0 + streak × 0.06)

Game over swell

• Background music fades to silence over 2 seconds while a descending tone plays
• New personal best: triumphant fanfare replaces the descending tone

Contract change required: No