Check One Two - Howling Check App

Howling that occurs at live events and performances. You can check the frequency bands where it's most likely to occur before actually causing feedback.

In front of the stage monitor, stay silent for 15 seconds. Then say "Check, one, two."
In about 30 seconds total, the dangerous frequency bands appear in Hz. You don't need a dedicated measurement microphone. It works with just your iPhone's microphone.

Lower the volume slightly. Change the direction of the microphone or speaker. The next steps to take also appear on the screen.

What's included:
・Monitor Check: Before the performance, identify the frequency bands most prone to causing howling.
・Analyzer: During the performance, display the sound currently being produced and highlight the frequency bands prone to howling with a red line. You can also switch to a spectrogram view.
・Stereo Recording: Record the performance or rehearsal audio as-is, without passing through any compressor or limiter.
・Register Your Voice: Simply read the words displayed on screen for 20 seconds.
・Metronome: Produces sound and light at a steady tempo. You can select the time signature and volume of the first beat.
・Tuner: Shows whether the note you play is in tune. The straighter the line, the more stable the pitch.
・Speaker Check: Plays sound in sequence from the audience's perspective: left, right, left and right simultaneously, and inverted phase.
・Frequency Guessing Quiz: Two types available—single note identification and A/B comparison.
・Recording Management: Delete any recordings anytime from here.

What you can use for free:
Even with the free version, you can use the Analyzer, Spectrogram, Monitor Check, voice registration, Metronome, Tuner, and Speaker Check. No account registration required.

The full version is a one-time purchase of 1,200 yen. It's not a subscription.
・Stereo Recording …… Free version: up to 5 minutes per recording, max 2 recordings / Full version: can record performances over 5 minutes in a single file and save unlimited recordings
・Monitor Check results …… Free version: up to 3 results / Full version: save unlimited results and compare with previous sessions at the same venue
・Frequency Guessing Quiz …… Free version: beginner level with 6 frequency bands (250Hz–8kHz), 2 sets per day / Full version: advanced level with 21 frequency bands (63Hz–16kHz), unlimited sets per day
・A/B Comparison …… Free version: pop music only / Full version: 4 genres

iPhone, iOS 17.0 or later. No account registration. No data collection.

Information page: https://check12.da-win.net/