CadenceSync – Music That Matches Your Stride

2 min read Original article ↗

CadenceSync app icon

Adjust music playback speed to match your running cadence. Pitch-preserving time-stretching keeps songs in key while you move.

Download on the App Store

100% on-device · Requires iOS 17+

Tempo matching

  • Detects each song's BPM during playback using peak detection, spectral onset analysis, and autocorrelation
  • Maps your target SPM to BPM using musically consonant ratios (1:1, 2:1, 1:2, 3:2, and more)
  • Applies changes gradually in 8% steps; small adjustments apply immediately
  • Toggle Tempo Match on or off; manually adjust speed from 0.5× to 1.5× when off

Cadence

  • Manual: set a target SPM from 100–200 (default 170)
  • Auto Detect: live cadence from the device pedometer during walking or running
  • Motion activity detection ensures cadence tracking only when you're on the move

Music library

  • Import a folder of audio files (MP3, M4A, WAV, AIFF, AAC, MP4, CAF)
  • Three bundled demo tracks load when the library is empty
  • Browse, search, play, delete tracks, or erase the whole library
  • Export library metadata as CSV from Settings

Shuffle

  • Persistent: tracks play history so songs aren't repeated until the full library has been heard
  • Classic: standard random shuffle that resets each session
  • Always Shuffle: optionally start each session with shuffle on and a random track
  • Play History shows recent tracks and remaining-songs count

Car Mode

  • On-device automotive activity detection, no GPS required
  • After sustained vehicle motion, Tempo Match turns off so music plays at normal speed
  • Stays latched until you turn Tempo Match back on
  • Optional: enable shuffle automatically when Car Mode activates

Pro & playback

  • Free tier: up to 10 songs in the library
  • Pro (one-time purchase): unlimited songs
  • Lock screen and Control Center controls via Now Playing
  • Background audio playback

1

BPM detection

Overlapping 20-second windows are analyzed with multi-threshold peak detection, spectral onsets, and autocorrelation. Results are clustered and normalized for double/half-time relationships.

2

Cadence mapping

Candidate SPM-to-BPM ratios are scored by tempo-shift size, ratio simplicity, and musical context. The best mapping is applied, capped at roughly 8% slowdown.

3

Playback

AVAudioEngine with pitch-preserving time-stretching changes tempo while keeping songs in key. Cadence changes are debounced and playback rate ramps smoothly in steps.

All processing runs on-device. Imported files stay in the app sandbox.