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Meter tab: a short line under START now explains that the app uses the microphone to measure sound frequency (not screen refresh rate) and that audio is analyzed live and never recorded. If you declined the microphone once, the system permission explanation now appears in your language instead of English.
Measure sound frequency in Hz — audio tuner, RPM counter & 50/60Hz meter
Frequency Counter is an audio frequency meter, Hz counter, and instrument tuner for Android. Measure the dominant sound frequency in real time with your phone's microphone — no extra hardware needed. Turn your Android phone into a four-in-one frequency lab: read any tone in hertz, tune instruments, count RPM, and verify 50/60 Hz mains hum. ▶ MAIN FEATURES • Frequency meter — dominant frequency in Hz, live from the microphone • Instrument tuner — tune guitar, piano, violin and more with cents precision • RPM counter — measure rotation speed from sound or vibration • 50/60 Hz mains mode — check power-line and electrical hum frequency • Real-time FFT with high-resolution peak detection (20 Hz–20 kHz) • Adjustable averaging, smoothing and sensitivity • Hold mode to freeze the reading • Dark mode, works fully offline, no account needed ▶ HOW TO USE 1. Open Frequency Counter and allow microphone access 2. Pick a mode: frequency, tuner, RPM or 50/60 Hz mains 3. Point the phone at the sound source 4. Read the live frequency in hertz, the musical note, or the RPM ▶ WHO USES FREQUENCY COUNTER • Musicians and instrument makers tuning by exact frequency • Audio and AV engineers checking tones and signal pitch • Electricians and technicians verifying 50/60 Hz mains • Mechanics and makers measuring motor and fan RPM • Piano tuners needing cents-accurate pitch • Students learning acoustics, sound and signal processing • DIY hobbyists testing speakers, buzzers and alarms Microphone permission required. External USB microphones supported.