StretchwiseSwitching from Entropy Piano Tuner to Stretchwise
Stretchwise is a piano tuning app for iPhone and iPad, made by Tempore. It reads Entropy Piano Tuner's own files (.ept) and its CSV exports, so the pitches and inharmonicity you recorded come with the piano. Stretchwise is on the App Store for iPhone and iPad.
Entropy Piano Tuner at a glance
- Price and licence
- Free software under the GNU General Public License, version 3 or later
- Latest release
- 1.2.0, from 2017; the most recent commit to its source is from February 2025
- Platforms
- Its source includes builds for Windows, macOS, Linux, Android and iOS
- Where to get it
- The source is on GitLab. Its website, piano-tuner.org, showed a domain-parking page when we checked, and we found no listing on the US App Store.
Checked 5 November 2026 in the project's GitLab repository (its tags, changelog, copyright notice and build scripts), on piano-tuner.org and in Apple's US App Store search.
Before you switch: a fair comparison
Entropy Piano Tuner is free and open source, and it runs on desktop computers as well as phones. Stretchwise runs only on iPhone and iPad, and it hasn't yet been used to tune real pianos in the field. See what we've tested, and what we haven't.
What Stretchwise does differently:
- Stretchwise measures each note's inharmonicity as you tune and rebuilds the piano's stretch curve after every saved note, by three-part tuning in Clean, Average or Expanded styles (how the curve is built).
- Per-note corrections, the reference pitch, the temperament and the stretch style are saved with each piano.
- It has a pitch raise with overpull by section and one-string raises (how it works).
- It includes 56 historical temperaments, and you can back up every piano to a file you keep.
Get your Entropy files onto the iPhone or iPad
Copy the .ept file, or a CSV export, to the iPhone or iPad, for example through iCloud Drive, another cloud drive or email. The .ept file carries more, so use it when you have it.
Import an Entropy file (.ept)
- In Stretchwise, tap the piano bar at the top of the tuning screen.
- In the list of pianos, expand Import & backup and tap Import a tuning file…
- Choose the .ept file. Stretchwise creates a new piano and selects it.
| In the Entropy file | In Stretchwise |
|---|---|
| The piano's name | The new piano's name (the file name if the piano has none) |
| Concert pitch | The piano's reference pitch |
| Recorded frequency and measured inharmonicity of each recorded key | A saved reading for that note, which also shapes the stretch curve |
| Keys with no recording | Left for you to measure |
| Calculated and tuned frequencies | Not imported: Stretchwise calculates its own targets |
Keys are matched through the file's own keyboard layout, so A4 lands on A4. Keys outside A0 to C8 are left out.
Import an Entropy CSV export
Import the CSV the same way. Stretchwise reads its Key index, Recorded frequency and Inharmonicity columns. Keys with a recorded frequency of 0 Hz count as not measured and are listed as skipped. The CSV doesn't include the piano's name or concert pitch, so the piano is named after the file and uses the standard A440 reference: set the reference pitch yourself if the piano is tuned elsewhere.
After the import
The import message says how many notes came in and lists up to three skipped lines with the reason. The imported readings appear on the piano's Overview. Check a few notes you know well the first time you tune an imported piano. If something doesn't look right, email support@tempore.net. Please send the file only if you're happy to share it.
Handy while you compare: the free piano tuning calculators use the same stretch and pitch-raise maths as the app.