What your microphone hears stays on your device.

Resonance Piano Tuner makes no network connections of any kind. It has no server to talk to. It works the same with Wi-Fi switched off.

• No account and no sign-in.
• No analytics, no advertising, no tracking, and no crash-reporting service.
• No third-party code. The app is built only on Apple's own system frameworks.
• No iCloud and no sync between devices. (If you back up your iPhone or iPad, Apple's backup includes the app's files, as it does for any app.)

Because nothing is sent off your device, the developer receives no data from the app. That is what Data Not Collected means on the App Store.

The app needs the microphone to hear the piano. Your iPhone, iPad or Mac asks for your permission the first time, with these words:

Resonance listens to your piano to measure inharmonicity and to tune it.

The sound is analysed on the device, in memory. The app keeps a rolling buffer of roughly the last ten seconds, which is overwritten continuously as it listens. What you see on screen are numbers worked out from that sound: frequencies, cents, levels.

While the app is open and the input is running, it listens in every view. The app never plays the microphone back, and it produces no sound of its own.

• iPhone and iPad: it listens only while the app is on screen, and the system shows its orange microphone dot while it does. You can take the permission away at any time in the Settings app, under Resonance › Microphone.
• Mac: you can stop it with Stop input in Setup, and take the permission away at any time in System Settings, under Privacy & Security › Microphone.

We will not tell you that audio is never recorded, because that would not be true. One kind of short sound file is saved, inside the session of the piano you are working on:

• Measurement clips. Each time a measurement strike is accepted, the app saves a clip of it, up to about 4 seconds long, next to the numbers it worked out. This happens automatically, both in the Measure step and when the app learns from clean strikes while you tune. It is there so that a measurement can be examined again later. There is no setting to turn it off.

A clip holds whatever the microphone heard during those few seconds: the note, the room, and possibly a voice if someone was speaking. The Survey, the needle and the strobe save no sound.

These files are stored inside the session on your device and nowhere else. The app cannot send them anywhere. They leave the device only if you export or copy the session yourself. (A developer command that saves the last 8 seconds of input also exists. It is switched off, and nothing in the normal app can trigger it.)

Sessions. A session is a folder on your device that holds one piano: the name you gave it, its layout, the survey, the measurements and their clips, the tuning curve, your progress and your settings. It also notes which audio input was used, by the identifier the system gives it. It holds no e-mail address, no account, no location and no contacts.

Logs. Each time it runs, the app writes a plain-text log of what it did, and passes the same lines to the system's own log. A log contains technical numbers, the names of your microphones, file paths and session names. It never contains sound.

Nothing is deleted automatically. Sessions and logs stay on your device until you remove them, and the app does not tidy up old logs by itself.

• iPhone and iPad: sessions and logs are in the Files app, under On My iPhone (or iPad) › Resonance. Remove a session in the app's Sessions list, or delete any folder there. Deleting the app deletes all of them.
• Mac: to remove a session, select it in Sessions and choose Move to Trash…. The folder, its measurements and its recordings go to the Trash, and you can put it back from there until you empty it. Reveal in Finder shows where a session lives, and Settings › Session storage shows how much space your sessions use.
• To remove logs on a Mac: the app has no button for this yet. Write to us and we will tell you where the folder is. Logs hold no sound.

A few commands exist so that you can ask for help. None of them sends anything by itself. Each puts something where you can see it, and what happens next is up to you.

• Export session makes a zip file of one session, including its sound clips. On the Mac it is Tuner › Export session folder (zip)…; on iPhone and iPad it is in Settings, and opens the share sheet.
• On iPhone and iPad, Settings also has Share log, which opens the share sheet with the log file, and Copy diagnostic data, which puts a block of text on the clipboard: your settings, the measurements, recent log lines, the name of the microphone and the session's name and file path. It contains no sound.

It goes nowhere unless you send it somewhere. So think before you send: a clip can hold a voice if someone was speaking.

Resonance Piano Tuner is sold through the App Store and the Mac App Store. Apple handles the purchase, the payment and the download under Apple's privacy policy. We never see your payment details. Apple may show developers combined sales figures, and usage or crash statistics from people who have agreed to share them with developers in their own Apple settings. The app itself adds nothing to that.

This website sets no cookies and has no analytics. It loads nothing from other companies: the fonts, the film and the scripts all come from the site itself.

It keeps two small preferences in your browser, and they never leave it:

• whether you have already seen the intro in this tab, so that it plays only once. This is forgotten when you close the tab.
• whether you switched the film's captions on, so that they stay the way you left them.

The live instruments on the home page run on made-up values in your browser. They do not use your microphone and make no sound.

Like any website, the pages are delivered by a hosting provider, which may keep ordinary server logs, such as the address a request came from and the page asked for. We do not use them to identify anyone. The App Store and Mac App Store buttons take you to Apple.

If you send an e-mail to support, we receive your address and whatever you put in the message, including any session you attach. We use it to answer you and to fix the problem, and for nothing else. We do not sell it, share it, or add you to a mailing list.

The app collects nothing from anyone, whatever their age.

If the app ever changes in a way that affects this page, the page will change first, with a new effective date at the top.