Turntable RPM: Platter Check

Turntable RPM and speed checker: lay your phone on the platter and Platter Check reads the speed from the phone's gyroscope, showing the deviation on a ±% needle so you can set 33⅓, 45 or 78 while you turn the pitch control. The same app measures wow & flutter and makes a printable strobe disc. ▶ SPEED • Measures until you tap Stop, with no time limit — adjust the pitch and watch the needle. • Target speeds 33⅓, 45, 78 and 16⅔, or a custom speed from 10 to 100 rpm. • Live speed, the average of the last 10 revolutions, deviation from the target in % and drift in %/min. • Repeatability: the spread of the per-revolution averages, so you see how steady the reading is. • The speed comes from the rotation rate itself, so the phone's distance from the spindle doesn't change it. • Calibrate once on a still table (5 seconds) to remove the gyroscope's offset. ▶ WOW & FLUTTER • Gyro mode: how evenly the platter turns — speed deviation as peak and 2σ in %, a 10-second trace and a spectrum up to 20 Hz with the once-per-revolution line marked. Slow (below 4 Hz) and fast parts are shown separately. • Test-tone mode: play a 3150 Hz or 3000 Hz test-tone record and hold the phone near the speaker. The app follows the tone's frequency and shows its deviation (peak and RMS, unweighted) and the speed worked out from the tone. This also catches an off-center or warped record. ▶ STROBE DISC • Create a printable strobe disc as a PDF for 50 Hz or 60 Hz mains. • Only rings with a whole number of bars: 50 Hz → 33⅓ (180 bars); 60 Hz → 33⅓ (216) and 45 (160). Any print size works. ▶ A LOG FOR EACH TURNTABLE • Save a result to a named turntable, with its cartridge and a note. • Compare two measurements of the same kind, for example before and after a belt change. • Delete with Undo. Export the log as a file and restore it from the exported text. • Up to 50 turntables and 2,000 measurements. ▶ GOOD TO KNOW • Speed and gyro mode need a phone with a gyroscope; the test-tone mode and the strobe disc work without one. • The gyroscope's scale can't be calibrated in the app. For the absolute speed, cross-check with a strobe disc. • Wow & flutter figures are plain, unweighted percentages and include sensor noise. You need your own test-tone record. • The strobe disc needs a light that flickers at twice the mains frequency (an incandescent bulb or a non-smoothed LED). The phone's screen is not used as a strobe. • Sensors and the microphone run only while a measurement is on screen. The microphone is used only in test-tone mode; the sound is analyzed live and no audio file is saved. • Your log is saved on this device. No sign-in. • Ads appear on the Log tab; full-screen ads can appear when the app opens, when you come back to it and sometimes after you save — never while a measurement or calibration runs.

Calibration no longer ends with “Too few sensor readings” on many recent phones: the gyroscope is now read at the phone's full sensor rate, so the 5-second calibration completes and speed measurements can start.