Bluetooth MIDI vs USB vs the microphone: how should your piano talk to the app?
For learning with an app, Bluetooth MIDI and USB MIDI are equally good: both send every key, how hard you pressed it and the sustain pedal, with a delay too small to matter for most practice. USB is slightly faster and never drops out; Bluetooth needs no cable. The microphone works with any piano, acoustic included, but it hears notes rather than reading them, so it's less certain with fast passages and thick chords and can't see the pedal.
The rest of this page explains the differences, with measured figures where they exist, and what to buy if your piano has no Bluetooth.
What does each connection actually tell the app?
A digital piano describes your playing as MIDI: "middle C down, velocity 64", "pedal down", "middle C up". Bluetooth MIDI and USB MIDI carry exactly the same messages; only the cable differs. The microphone gets none of that. It gets sound, and the app has to work out which keys made it.
| Bluetooth MIDI | USB MIDI | Microphone | |
|---|---|---|---|
| Which keys | Exact | Exact | Recognised from the sound; occasionally missed or misheard |
| Velocity (how hard) | Exact, 1 to 127 | Exact, 1 to 127 | A rough estimate from loudness |
| Sustain pedal | Yes | Yes | No |
| Chords | Every note, however many | Every note, however many | Good for most beginner and intermediate chords; less sure with thick, low ones |
| Delay | A few to about 20 ms (see below) | A few ms | Noticeably longer: the app waits to hear the pitch |
| Reliability | Very good close to the piano; can drop out at a distance | Very stable once plugged in | Depends on the room: noise, other music and the app's own sound get in the way |
| Works with | Pianos with Bluetooth MIDI | Pianos with USB to Host (plus a cable or adapter) | Any piano, acoustic or digital |
Is Bluetooth MIDI fast enough? (latency)
Yes, for practice. When you play a digital piano, you hear the piano's own sound instantly: the connection only affects how quickly the app sees the note. That delay matters for scoring and for how quickly the screen reacts, not for what you hear.
Measured figures are scarce, so here is one careful study. In a 2019 paper from McGill University (Wang, Mulder and Wanderley), researchers timed the path from a button press to sound coming out of a computer:
- a USB MIDI device: about 4 ms;
- a minimal Bluetooth MIDI device: about 7.5 ms, and their own Bluetooth MIDI sensor interface about 19 ms;
- replacing a wired MIDI link with a Yamaha Bluetooth MIDI adapter added about 12 ms each way.
The reason is how Bluetooth Low Energy works: data goes out in regular "connection intervals", and the paper notes the Bluetooth MIDI specification asks for an interval of 15 ms or less (the Mac they tested chose 11.25 ms). These were measured on computers; phones and pianos differ, so treat them as orders of magnitude rather than promises.
For comparison, PianoKite gives full timing credit to a note played within 100 ms of the beat (75% within 200 ms, half within 300 ms). A Bluetooth delay of 10 or 20 ms is small next to that. Where it can matter is in fast, rhythmic playing at full speed, and there a cable is the safer choice.
Can a piano app hear my piano through the microphone?
Yes. PianoKite listens through the phone's microphone and recognises the notes as you play them, on an acoustic piano or a digital one without MIDI. How it does it explains its strengths and limits:
- Two kinds of listening. A short window of sound (32 ms) catches the moment a hammer hits the strings; a longer one (128 ms) is needed to tell the pitches apart. That's why a note is recognised a fraction of a second after you play it. The app knows the delay and subtracts it when it scores your timing, so you're not marked late for it, but in Wait mode the music moves on a moment later than it does over MIDI.
- Chords. It picks out several notes at once, removing each found note's overtones before looking for the next, so an octave or a fifth above isn't mistaken for a note you didn't play. It also knows which notes the score expects next and listens for them more readily. Thick, low chords are the hardest, because their overtones overlap.
- The app's own sound. When the phone plays the other hand or a count-in, the microphone hears it too. The app knows what it's playing and needs much more evidence before it counts those notes as yours, but headphones are still the cleanest fix.
- No pedal, rough velocity. Sound tells you roughly how loud a note was, not exactly how fast the key moved, and nothing about the pedal.
- Private. The audio is analysed on the phone and never uploaded. A short sound check the first time measures the room's background noise and your piano's tuning, which on an acoustic piano is often a little off standard pitch.
In practice the microphone works well for melodies and most beginner and intermediate pieces. For fast runs, dense chords, the pedal, or the most precise scores, MIDI is better. More tips in learning on an acoustic piano.
What the extra information is used for
With MIDI the app knows not just which notes but how you played them. In PianoKite, velocity lets the review after a run comment on your touch, how evenly you play. The pedal reaches the app too: in pieces with pedal marks you can choose to work the pedal yourself, and the app checks your pedalling instead of doing it for you. With the microphone these parts of the feedback are missing or rougher; notes and rhythm are still scored.
Which pianos have which connection?
| Piano | Bluetooth MIDI | USB to Host | Guide |
|---|---|---|---|
| Roland FP-10 | Yes | Yes | Roland FP-10 |
| Roland FP-30X | Yes (plus Bluetooth audio) | Yes | Roland FP-30X |
| Yamaha P-45, P-125 | No | Yes | Yamaha P-45 and P-125 |
| Casio, Kawai, Korg and others | Varies by model | Varies by model | Other Bluetooth MIDI pianos |
| Acoustic pianos | No | No | Microphone |
Watch out for Bluetooth audio on its own. It lets the piano play your phone's music through its speakers, but it doesn't send the notes you play. The word to look for is MIDI.
Which should you use?
| Your situation | Use |
|---|---|
| The piano has Bluetooth MIDI | Bluetooth. Nothing to buy, no cable across the music stand. |
| Bluetooth MIDI keeps dropping, or you play fast, rhythmic music at full speed | USB, if the piano has it. |
| The piano has USB to Host but no Bluetooth | A USB cable and adapter for your phone. |
| Acoustic piano, or a digital piano with neither | The microphone, ideally with headphones in a quiet room. |
| You're away from your piano | The on-screen keys: no piano needed, fine for learning a piece's notes. |
My piano has no Bluetooth: what should I buy?
A USB cable (cheapest and most reliable)
If the piano has a USB to Host port, a cable is all you need:
- Android: a USB-C to USB-B cable, or the usual USB-A to USB-B ("printer") cable with a USB OTG adapter. See connecting a piano to Android.
- A computer (the web app in Chrome or Edge): a USB-A or USB-C to USB-B cable straight into the computer.
On iPhone and iPad, a USB or Bluetooth connection needs the iPhone app, which is coming to the App Store. Safari doesn't support Web MIDI, so in the browser on an iPhone only the microphone and the on-screen keys work.
In the browser, USB is also the simpler route: a Bluetooth MIDI piano first has to be set up in the computer's own Bluetooth or MIDI settings before the browser can see it, and how depends on the system.
A Bluetooth MIDI adapter (wireless)
Small adapters can give a piano without Bluetooth a Bluetooth MIDI connection. Two kinds:
- For a USB to Host port: for example Yamaha's UD-BT01, which plugs into the piano's USB TO HOST port and needs power from a USB AC adaptor, or CME's WIDI Uhost, which adds Bluetooth MIDI to class-compliant USB MIDI instruments.
- For 5-pin MIDI sockets: adapters such as Yamaha's MD-BT01 or CME's WIDI Master plug into MIDI In and Out.
Compatibility varies. An adapter has to work with your particular piano (some need the piano's USB port to behave as a standard, driver-free MIDI device, some need their own power) and present itself as a standard Bluetooth LE MIDI device to the phone. Check the maker's compatibility notes for your piano model before buying. We haven't tested any adapter with PianoKite, so we can't recommend a specific one, and as the measurements above show, an adapter adds some delay compared with a cable.
If your piano has USB to Host, the honest advice is: try a cable first. It costs less, adds no delay and needs no charging. Buy an adapter if the cable really is in the way.
Does it matter for learning?
Less than it might seem. Any of the three lets you follow the score, learn notes in Wait mode, play along at a slower tempo and see which bars need work. MIDI makes the feedback sharper (touch, pedal, every note of every chord), so if your piano has Bluetooth MIDI or USB, use it. If it doesn't, the microphone is a real option, not a fallback to apologise for. Start with something slow and clear from the beginner pieces.