Is Clearsing free?
Yes. Every exercise, the programs and the progress view are free, and there is no account. I may add a paid Pro tier with extras later, but what you see today stays free.
Do I need to read sheet music?
No. You hear a pattern and sing it back; the target notes are blocks on a piano roll, not notation. Note names are shown on the side if you want them.
What microphone do I need?
The one built into your laptop or phone works. If you have a USB microphone, or an audio interface such as a Focusrite Scarlett with a dynamic or condenser mic, the pitch tracking is cleaner and less bothered by room noise. You pick the input device and, on an interface, the channel in Settings. Headphones matter more than the mic, though: without them the piano leaks back in.
Does it work on iPhone and Android?
Yes, in the browser. On iPhone use Safari; on Android and on a computer, Chrome or Edge. Firefox I haven't tested. There is nothing to install, though you can add it to your home screen.
Is my voice recorded or sent anywhere?
No. The pitch detection runs in your browser and the audio is discarded as soon as it's analyzed. I don't record anything, and there is no server that hears you. Progress is saved only in the browser on your device, so clearing site data clears it too.
I don't know my vocal range. Where do I start?
Take the vocal range test in Tools; it takes about two minutes. You sing a low note, then a high one, and the app finds your comfortable limits. Every exercise is then transposed to fit that range. You can also pick a preset such as tenor or alto and measure later.
How accurate is the pitch detection?
On a steady tone, within a few cents (a cent is a hundredth of a semitone). The detector listens roughly between 60 and 1100 Hz, bass to soprano. The scoring tolerance is yours to set, from ±20 to ±100 cents; the default is ±50, half a semitone. Glides and lip trills get a wider tolerance on purpose.