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 the effects page from the player

    Start the song and tap the effects button on the Now Playing bar. Equaliser, Karaoke and Pitch are three tabs of the same page, so everything below happens without leaving the song that is playing.

  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

    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.

  5. 05

    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. An instrumental you export is cached by content, so a song is only ever processed once.

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.
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.
Does it change my file?
Only if you ask it to. Effects are applied to playback and leave the file alone. Exporting an instrumental writes a new file and keeps the original, and the export is cached by content so a song is separated once rather than every time.

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Bring your own music

Every part of bMusic works for 15 days from the day you install it, with nothing held back. Send one album across and hear it on your own headphones.

Download on the App Store

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