Check1.2 - Feedback Checker
PA feedback & ear training
Only for iPhone
Free · In‑App Purchases
iPhone
Feedback-prone bands in Hz. Seven are free: Monitor check, Analyzer, Spectrogram, Register your voice, Metronome, Tuner, Speaker check. No sign-up or subscription.
Check1.2 finds the frequencies most likely to feed back, in Hz.
Before the show, you cannot tell which frequency to pull down.
The iPhone microphone is all you need. No measuring instrument, no external microphone.
The Full version is a one-time purchase. It is not a subscription.
FREE AND FULL
- Stereo recording: free is 5 minutes a take, 2 saved. Full records a whole show in one take and keeps as many as you like.
- Monitor check results: free keeps 3. Full keeps as many as you like, compares with your last visit to the same venue, and keeps what you changed.
- Normalize: free works on takes up to 5 minutes. Full works on longer takes too.
- Ear training quiz: free is Beginner, 6 bands from 250 Hz to 8 kHz, 2 sets a day. Full adds Advanced, 21 bands from 63 Hz to 16 kHz, and unlimited sets.
- A/B comparison: free is Pop. Full has four genres.
Deleting a recording or a result does not give the slot back. Use Restore Purchases on a new phone.
Analyzer, Spectrogram, Monitor check, voice registration, Metronome, Tuner and Speaker check are free. No account needed.
For people learning PA, people doing the PA on the day at a small venue with no dedicated engineer, and people training new PA staff at a live house.
FEATURES
- Stereo recording, no compressor and no limiter.
- Metronome with a volume slider and a beat-1 accent you can turn on or off.
- Tuner. Press a note name to hear it as a sine tone.
- Speaker check.
- The screen stays on while you check.
MONITOR CHECK (BEFORE THE SHOW)
From 15 seconds of ambient sound and your voice, it lists the bands most likely to feed back, as a number and a word, like "about 250 Hz (muddy)". While recording, a green, yellow or red lamp warns you when feedback is close. Hum and hiss are reported in words too. Register your voice and it also reports muddy (200-500 Hz), boomy low end (63-125 Hz), harsh (2-5 kHz) and sibilance (5-8 kHz).
A tone that stays after your voice stops is close to feedback. It listens 3 seconds to tell it from reverberation. Results stay on your iPhone with the venue name and a note, so you can compare next time.
What you do next is the real work. Turn the level down. Move the speakers or the microphone. If it still feeds back, cut the band you found with EQ, a little at a time.
ANALYZER (DURING THE SHOW)
50 Hz to 18,000 Hz, about 11.7 Hz steps, redrawn about 23 times a second.
- Green line: the sound now. White: Peak Hold. Orange dashed: the strong band.
- A tone that stands out from its neighbours and keeps doing so gets a solid red line. Musical notes are told apart by their harmonics and get no red line.
- Drag the screen to read the frequency there. Pick an instrument (All, Drums, Bass, Guitar, Vocals, Piano) for notes written for it.
- If the waveform goes flat on top, it tells you it is clipping.
- Press a note name for a sine tone, to check a speaker or a band.
FREQUENCY QUIZ
Name the frequency of a sine tone, or compare a band track with and without EQ and name the band that changed. With headphones and Advanced (full version), 63 Hz and 125 Hz join in.
HOW TO USE
1. Monitor Check measures the ambient sound levels for 15 seconds.
2. Record your voice.
3. Press "See results" and wait 3 seconds without speaking.
4. Read the bands most likely to feed back, and what to do next.
5. Fix the level and the speaker and microphone directions.
PRIVACY
Recording, analysis, voice registration, results and venue notes stay on your iPhone. The app never sends them anywhere. The only network use is Apple's in-app purchase. No ads, no tracking.
NOTES
This app is not a measuring instrument. Start quiet and raise the level slowly. Stereo recording works on supported models only; others record in mono, and the app tells you first. Below 150 Hz the iPhone microphone cannot measure accurately, so feedback detection is off there; the Analyzer still draws it. dB is not calibrated, so this is not a sound level meter.
Ratings & Reviews
- This app hasn’t received enough ratings or reviews to display an overview.
Compare with last time at the same venue (Full version).
- "Compare with last time" in Past results. For the same venue, the feedback-prone bands are listed as both times, this time only, and last time only. Each result can also keep "what you changed" (EQ cuts, etc.). Both are in the Full version.
- The Tuner and the Analyzer can now play the note you pick.
- Note buttons (C D E F G A B) on the Tuner and the Analyzer. Press one to hear that note as a sine tone. Flat and sharp step by a semitone, and you can change the octave. There is a volume slider.
- The Metronome has a volume slider. The accent on beat 1 is now on or off.
- The Monitor check start screen now tells you how to set up the microphones and the stage monitor send. The results now say when no band appeared at that level, and remind you to return to show level when you finish.
The developer, Daisuke Kawaue, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Collected
The developer does not collect any data from this app.
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- Daisuke Kawaue
- Size
- 16.6 MB
- Category
- Music
- Compatibility
Requires iOS 17.0 or later.
- iPhone
Requires iOS 17.0 or later.
- iPhone
- Languages
- English and Japanese
- Age Rating
4+
- 4+
- In-App Purchases
Yes
- Full version $6.99
- Copyright
- © 2026 Aiba