Centerline

Available now on Android

Pitch-standard guide

A4 calibration guide for guitar tuners

Most guitars live at A4 = 440 Hz, but some rehearsals, keyboard rigs, or recorded backing tracks drift to another center. Centerline's public Android release supports A4 calibration from 432 to 446 Hz after the one-time unlock. The practical use case is matching another instrument or session that has already declared the target, then keeping your guitar aligned to that same center.

Get it onGoogle Play

Free standard tuningUS $3.99 one-time unlock

How to use it

Change the center only when another source requires it.

A4 calibration changes what "in tune" means across the entire instrument. At 440 Hz, standard E, A, D, G, B, and E match modern concert pitch. If a rehearsal keyboard, reference track, or ensemble is set to 442, 438, or anywhere from 432 through 446 Hz, your tuner must adopt that same center or every note will be slightly offset even when your strings look visually perfect. That is why A4 matters more in group contexts than in solo practice.

Centerline keeps the control straightforward in the current Android release: pick the calibration, then tune as normal. Because there is no reference tone generator, it is not designed for "guess and compare" workflows. You should already know the target from another instrument, a conductor, a rehearsal note, or the session engineer. Once that target is set, the app will keep your guitar aligned to the chosen center just like it does at 440.

Centerline workflow

  1. Leave the app at 440 Hz unless another instrument or session explicitly says otherwise.
  2. Unlock calibration once if the alternate A4 control is still locked.
  3. Set the app to the required standard anywhere from 432 to 446 Hz.
  4. Tune each string normally in Guitar, Simple, or All strings after the new center is active.
  5. Return to 440 Hz after the rehearsal if that is your default home setup.

What the public app can do today

  • The Android release includes four displays: Simple, Guitar, Strobe, and All strings.
  • A4 calibration is part of the one-time unlock and covers the practical 432 to 446 Hz range.
  • It works best when you are mirroring an already known calibration standard from another instrument, room, or session.

If nobody else in the room asked for a different standard, stay at 440 Hz. Changing A4 "just to try it" creates unnecessary mismatch with recordings, pedals, and bandmates.

When it matters

Useful in ensembles, sessions, and careful practice.

Guitarists do not usually think about A4 until something else is dictating the pitch center. Pianists, orchestral instruments, or archived recordings can do that. Some players also practice against material that was transferred slightly off concert pitch. In those cases, a tuner that can match the agreed standard saves time because every open string and every fretted note start from the same reference.

Centerline remains intentionally narrow: it is a fast, private guitar tuner, not a full lab instrument. That is why the current app focuses on a clean adjustable center, clear pitch displays, no ads, no account, and a one-time unlock instead of layering on extra audio or network features that most tuning sessions do not need.

Related guides

More Centerline tuning references

Drop D tunerKeep the sixth string aligned after you move away from standard. DADGAD tunerRepeated notes make a clean target sequence more important. Open G tunerAnother whole-instrument retune that benefits from a final cleanup pass. Half step downLower every string evenly while the neck tension settles. Strobe vs needleChoose the display that makes fine calibration corrections easiest. Privacy policySee how the app stays offline and how the website measurement is sanitized.

These notes describe the Centerline Android release available today.