Karaoke and practice on an iPhone: vocals out, key moved, bar looped

Learning a song off a record means playing the same four bars twenty times, slower than they were recorded, sometimes in a different key, and often without the original singer in the way. Here is how to do all of that to a file you own, on a phone, with nothing uploaded anywhere.

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The bMusic settings screen, with playback, library and sync options

Why the usual tools are the wrong shape

The tools built for this are either desktop software or a subscription that only works on its own catalogue. Neither fits the moment it is actually needed — on a train, in a rehearsal room, in the twenty minutes before a lesson — and the catalogue-shaped ones cannot touch the recording you were given by the person who wrote it.

Backing tracks have the same problem from the other end. A karaoke version exists for a few thousand songs, is a different arrangement from the one you learned, and often in a different key from the one you sing. The recording you want to practise against is the record itself.

What a player can do instead is process the file it is already playing: cancel what sits in the middle of the stereo image, shift the pitch without dragging the tempo with it, slow the whole thing down without dropping it an octave, and loop a section precisely enough to be useful. All of that is arithmetic on audio the phone already has, so it needs no catalogue, no account and no connection.

Step by step

Setting up a practice session

  1. 01

    Get the song onto the phone

    Any of the usual ways in: Wi-Fi transfer from a computer, AirDrop, the Files app, a link or your own WebDAV server. Lossless is worth using here — MP3, AAC, M4A, ALAC, FLAC, OPUS, WAV, AIFF all import untouched, and vocal cancellation has more to work with when the stereo image has not been through a low bitrate.

  2. 02

    Open Karaoke from the player

    Start the song and tap the karaoke button on the Now Playing bar. Karaoke is a page of its own and stays on from song to song until you switch it off, so everything below happens without leaving the music.

  3. 03

    Take the voice out, as far as it will go

    Karaoke cancels the centre of the stereo image between 150 Hz and 10 kHz, where a lead vocal usually sits, and leaves the kick drum and the bass alone. The strength is a slider rather than a switch, because how much can come out before the record starts sounding hollow depends on the mix.

  4. 04

    Choose Standard or Advanced

    Standard is the slider above, and it is free for good. Advanced takes the voice out far more cleanly, including on the records the slider can do little with, but only for a song you have processed: with Advanced chosen, tap Process on the Karaoke page and stay there for the few minutes it takes — the music keeps playing, and leaving the page or the app stops it. It is part of bMusic Pro, and everything is unlocked for the first 7 days. Whichever you pick is what you hear, what an exported backing track is made of, and what a sing-along take is recorded over.

  5. 05

    Move the key and slow it down

    Pitch shifts up to six semitones either way and leaves the tempo where it was; speed runs from half to double and leaves the pitch where it was. Both are useful on their own — a song a tone too high to sing, or a solo too fast to hear — and they compose.

  6. 06

    Loop the bar you keep missing

    Set an A–B loop around the passage and it repeats until you stop it. That, plus half speed, is most of what practising a part actually is. When it is time to hear yourself, the sing-along recording captures your take against the backing on the same clock, so the two line up when you play it back.

A mono recording has no middle to cancel, and bMusic says so instead of offering a slider that does nothing. Everything else on the page still works on it.

What the phone is doing

Cancelling, not separating
The vocal is removed by subtracting what is common to both channels in the range it lives in. It is honest arithmetic with an honest limit: a heavily processed or doubled vocal survives it, and reverb usually does too.
Pitch without tempo, tempo without pitch
A phase vocoder moves the key up to ±6 semitones with the timing intact, and the speed control runs 0.5–2× without dropping the singer an octave. Practising a part in your own key is a different exercise from practising it slowly, and neither should force the other.
A room, not a track
The ten-band equaliser and your headphones’ own correction curve are on the same page, so what you practise against sounds like the record rather than like a phone.
Everything stays on the device
No stems are uploaded, no account is involved, and it works on a song nobody else has heard. Nothing is processed behind your back: Advanced works on a song only when you tap Process, and keeps two files for it on the iPhone — the voice and the backing track — which you can preview on their own. Playback, the export and the sing-along recording all use those two files, so a song is processed once. They stay until you delete them — on the Karaoke page or in Settings → Karaoke Files — or delete the song, and they are not included in backups.
Free, with two parts that are not
Karaoke, the backing-track export and the sing-along recording are free for good — the mode itself, not a sample of it. Advanced is the better-sounding version of those same three things and is part of bMusic Pro: one purchase rather than a subscription, with every feature open for the first 7 days. After that karaoke carries on at the standard setting; the songs you processed stay on the phone and come back into use when you buy or restore Pro, and the files you exported while you had it stay yours. Deleting processed files costs nothing. Slowing a song down or speeding it up is the playback speed control, which is part of bMusic Pro too; the A–B loop is not.

FAQ

Karaoke and practice: the usual questions

How good is the vocal removal, really?
On a normally mixed stereo record — voice in the middle, instruments spread around it — it is good enough to sing over. On a dense modern master, a doubled or heavily panned vocal, or anything mono, the voice partly stays. It is centre cancellation rather than source separation, and the app does not claim otherwise. Advanced is the answer to exactly that limit: you process a song once on the iPhone, which takes a few minutes, and it pulls the voice out of records the slider cannot.
Does changing the key make it sound like a chipmunk?
No. Pitch and tempo are moved independently, so a song shifted down two semitones plays at its original speed and a song at half speed keeps its original key. Very large shifts on very dense material do get artefacts, which is why the range stops at six semitones.
Can I record myself singing along?
Yes. The take is recorded against the backing on the same clock, then mixed down, so the two stay in time and the result can be shared. It is not a multitrack studio; it is the thing you actually wanted when you pressed record.
Does any of this need a connection?
No. All of it runs on the device against files you already have, so it works on a plane, on the underground and in a rehearsal room with no signal. The one exception is the first time you process a song with Advanced, which asks before a one-time download of what it needs; after that it runs with no signal too.
Does it change my file?
Only if you ask it to. Effects are applied to playback and leave the file alone. Processing a song for Advanced keeps the voice and the backing track as two new files beside it, and exporting an instrumental writes a new file too; the original is never touched.
Does karaoke cost anything?
Taking the voice out with the slider, exporting the backing track and recording yourself over it are free for good, on as many songs as you like. Advanced — the much cleaner version — is part of bMusic Pro, and the line is the same wherever you meet it: listening, exporting and singing along all follow whichever of the two you chose, and a song not yet processed asks to be processed rather than quietly getting Standard under the Advanced name. Every feature is open for the first 7 days; after that karaoke keeps working at the standard setting, processed songs wait on the phone until you buy or restore Pro, and anything you already exported is a file of yours that nobody takes back.

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iPhone, iPad and Mac · iOS 18.0 or later · Android 8.0 or later · MP3, AAC, M4A, ALAC, FLAC, OPUS, WAV, AIFF