Web app detects guitar string pitch via phone accelerometer pressed against the guitar body; alias-correction maps low sample rates to actual string frequencies.
Key Takeaways
Press phone firmly against guitar body, pluck a string; pitch is detected from the strongest axis among X, Y, Z and combined |a| magnitude.
Alias-correction is applied so even undersampled IMUs can resolve target frequencies back to actual string pitches.
Works best on Android with high-rate IMU; motion permission required; iOS and low-rate sensors will struggle.
50 Hz or 200 Hz sample rates are typical phone IMU limits, both below the 82 Hz low E2 string without aliasing tricks.
Hacker News Comment Review
The alias-recovery approach is the core technical bet: if sample rate is known and targets are constrained to six string frequencies, aliased peaks are still exploitable, but noisy signals make alias rejection unreliable.
Microphone-as-surveillance concern is largely dismissed; phone mass vs. sound-wave force (F=ma) makes airborne audio pickup far below sensor sensitivity, unlike direct contact vibration.
Commenters confirm the sensor is surprisingly sensitive to contact vibration beyond guitar use, including heartbeat detection through a chest-placed phone.
Notable Comments
@JoheyDev888: Explains alias recovery: known sample rate plus constrained string targets makes aliased peaks usable; messy signals are where rejection fails.
@tiluha: Placing phone on chest while lying down shows clear heartbeat on the graph, confirming contact-vibration sensitivity.
