I have a couple of ways to split a song:

• With Logic Pro for iPad - In the update for 2024, there’s a way to split a song into tracks (bass, drums, other, vocals), this feature is called stem splitter.
• With demucs which is an open source tool capable of separating drums, bass, and vocals from the rest of the accompaniment
  • It has a feature where it can split a song using more instruments (bass, drums, guitar, other, piano, vocals), in this mode I can keep important tracks in the backing track such as the “other” and “piano” tracks which make the backing track feel complete.

In this article I show how to use demucs to split a song into tracks.

Splitting a song with Demucs

High level steps

• Install essential tools
  • git
  • python
• Download dependencies (there’s an automated step to download these below)
  • Install yt-dlp to download your song (if you have your song skip this step).
  • Install demucs to split the track.
  • Install ffmpeg to combine selected tracks into a combined track.
• Download your song with yt-dlp
• Separate the track with demucs
• Join the drums/bass/other tracks with ffmpeg into a track that you can use as your backing track!

Download demucs dependencies

The assumption is that you already have git and python installed.

I’ve created a project that has a file with all the dependencies to install, you just need to clone the repository and use the requirements.txt file to install the dependencies.

git clone https://github.com/mauriciopoppe/open-mic/
cd open-mic
python3 -m venv venv
source venv/bin/activate
python3 -m pip install -r requirements.txt

Download your song

I’ll create a backing track with bass, drums, piano and other for the song December 21 by Prince Royce

First let’s download the song assuming that it’s on Youtube:

yt-dlp -x --audio-format mp3 <link-to-song>

Example:

yt-dlp -x --audio-format mp3 "https://www.youtube.com/watch?v=A9B1Uo-VQas"
[youtube] Extracting URL: https://www.youtube.com/watch?v=A9B1Uo-VQas
[youtube] A9B1Uo-VQas: Downloading webpage
[youtube] A9B1Uo-VQas: Downloading ios player API JSON
[youtube] A9B1Uo-VQas: Downloading android player API JSON
[youtube] A9B1Uo-VQas: Downloading player b46bb280
WARNING: [youtube] A9B1Uo-VQas: nsig extraction failed: You may experience throttling for some formats
         n = CN0_8RV0LjPMw_i9xJs ; player = https://www.youtube.com/s/player/b46bb280/player_ias.vflset/en_US/base.js
WARNING: [youtube] A9B1Uo-VQas: nsig extraction failed: You may experience throttling for some formats
         n = it19Djd_eJ-wpANfMuK ; player = https://www.youtube.com/s/player/b46bb280/player_ias.vflset/en_US/base.js
[youtube] A9B1Uo-VQas: Downloading m3u8 information
[info] A9B1Uo-VQas: Downloading 1 format(s): 140
[download] Destination: Prince Royce - Dec. 21 (Official Video) [A9B1Uo-VQas].m4a
[download] 100% of    3.30MiB in 00:00:00 at 7.11MiB/s
[FixupM4a] Correcting container of "Prince Royce - Dec. 21 (Official Video) [A9B1Uo-VQas].m4a"
[ExtractAudio] Destination: Prince Royce - Dec. 21 (Official Video) [A9B1Uo-VQas].mp3
Deleting original file Prince Royce - Dec. 21 (Official Video) [A9B1Uo-VQas].m4a (pass -k to keep)

The track is downloaded in the same location as where the command was run.

Next let’s use demucs to separate the track into different instrument tracks.

demucs -n htdemucs_6s --mp3 -j 2 <path-to-downloaded-song>

Example

demucs -n htdemucs_6s --mp3 -j 2 "Prince Royce - Dec. 21 (Official Video) [A9B1Uo-VQas].mp3"
Selected model is a bag of 1 models. You will see that many progress bars per track.
Separated tracks will be stored in /Users/mauriciopoppe/go/src/github.com/mauriciopoppe/open-mic/separated/htdemucs_6s
Separating track Prince Royce - Dec. 21 (Official Video) [A9B1Uo-VQas].mp3
100%|██████████████████████████████████████████████████████████████████████| 216.45/216.45 [01:28<00:00,  2.46seconds/s]

demucs created multiple files in the directory separated, let’s list them:

tree separated/
separated/
└── htdemucs_6s
    └── Prince Royce - Dec. 21 (Official Video) [A9B1Uo-VQas]
        ├── bass.mp3
        ├── drums.mp3
        ├── guitar.mp3
        ├── other.mp3
        ├── piano.mp3
        └── vocals.mp3

Finally let’s join the bass, drums, other, piano tracks with ffmpeg into the combined file combined.mp3.

cd separated/htdemucs_6s/Prince\ Royce\ -\ Dec.\ 21\ \(Official\ Video\)\ \[A9B1Uo-VQas\]/
ffmpeg -i bass.mp3 -i drums.mp3 -i other.mp3 -i piano.mp3 -filter_complex amix=inputs=4:normalize=0 combined.mp3

Let’s compare the original song with two versions of the backing track, one with bass and drums (no voice or guitar) and the other with bass, drums, other and piano (no voice or guitar).

demucs is an amazing tool and so useful for open mics!