engram

iOS app that listens to live audio and generates a continuous thermal print strip — a procedural visual record of a performance.

Every 5 seconds, the mic captures a window of audio. A spectral analysis pipeline extracts features from it. Those features drive a flow fiber renderer that draws a unique 32×32 pixel glyph. Twelve glyphs composite into a 384×32 row. Rows accumulate into a strip meant to scroll out of a thermal printer in real time.

No two performances produce the same strip.

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How it works

mic → ring buffer → FeatureExtractor → SigilRenderer → GlyphState → PrintQueue
                         (5s tick)           (32×32)     (384×32 rows)

Audio pipeline (Audio/)

• MicCapture — ring buffer at hardware sample rate (48 kHz on device)
• FeatureExtractor — vDSP FFT → spectral centroid, rolloff, bandwidth, flatness, chroma, MFCC, onset detection, HPSS ratio, tempo

Glyph renderer (Glyph/)

• SigilRenderer — flow fiber algorithm. Builds a 32×32 vector field from chroma interference waves, traces streamlines through it. Each pixel is computed, not drawn.
  • chroma[12] → field shape (each pitch class bends the field in its angular direction)
  • hpssRatio → fiber length (harmonic = long smooth curves, percussive = short tangles)
  • rms → seed density (loud = dense, quiet = sparse)
  • spectralFlatness → turbulence (tonal = smooth, noise = chaotic)
  • onsetTimes → seed positions (rhythmic events leave their mark)
  • deltaRms / deltaSpectralCentroid → burst turbulence at transitions
• GlyphContext — smoothed RMS, glyph index, previous frame (persists across renders)
• GlyphState — accumulates 12 glyphs into a 384×32 composited row

Pipeline (Pipeline/)

• AnalysisCycle — 5s Timer drives the full mic → features → glyph → row cycle

Archive (Archive/)

• SessionStore — saves glyphs and rows as PNGs to Documents/sets/<session>/
• StripStitcher — composites all rows into a single full-strip PNG on stop

Printer (Printer/)

• PrintQueue — actor-backed async queue; dequeues rows and sends to printer
• PrinterProtocol — printRow(_ image: CGImage) async throws
• ConsolePrinter — logs row dimensions (placeholder for ESC/POS)
• MockPrinter — no-op, used in DEBUG builds

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UI

Two tabs:

• Record — START/STOP, live 12-cell row preview, elapsed time, glyph count
• Archive — browse past sessions, view strips, inspect individual glyphs

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Requirements

• iOS 16+
• Xcode 15+
• XcodeGen (brew install xcodegen)

Build

xcodegen generate
open Engram.xcodeproj

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Project layout

Engram/
  App/          EngramApp.swift
  Audio/        MicCapture, FeatureExtractor, FeatureFrame
  Glyph/        SigilRenderer, GlyphState, GlyphContext
  Pipeline/     AnalysisCycle
  Archive/      SessionStore, StripStitcher
  Printer/      PrintQueue, PrinterProtocol, ConsolePrinter, MockPrinter
  UI/           ContentView, LiveStripView, StripScrollView,
                ArchiveBrowser, StripDetailView, RendererPreviewView