チェックワンツー - ハウリングチェックアプリ

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

In front of a 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.

The Analyzer, Spectrogram, Monitor Check, and Voice Registration features are all free.
The only paid feature is unlimited access to ear-training quizzes (one-time purchase of 500 yen). It's not a subscription.

iPhone・iOS 17.0 or later. No account registration required. No data collection.

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