How to Slow Down a Song for Practice Without Changing the Pitch
Slowing a record down to learn from it is older than the software. Jazz players in the 1950s put 45 rpm singles on at 33 rpm: 26% slower, a fourth lower, and transposed in their heads. The first programs that slowed a recording without lowering it followed in the late 1990s: Roni Music's Amazing Slow Downer in 1997 and Transcribe! version 2 in August 1999. Today the same job runs in a browser tab, and a stem player adds the one thing none of the earlier tools had: the instrument you are learning can be taken out of the mix while the rest plays slower.
Four ways to slow a song down, pitch kept
| Way | Cost | Range | Loop a section | Mute one instrument | Keeps a file |
|---|---|---|---|---|---|
| YouTube playback speed (gear icon, Playback speed) | free | 0.25x to 2x, in steps | no | no | no |
| Audacity, Effect > Pitch and Tempo > Change Tempo | free | any value | select and play | no | yes, after export |
| Amazing Slow Downer, Transcribe!, Music Speed Changer | paid or freemium apps | wide, 20% to 200% in Amazing Slow Downer | yes | no | some |
| StemPlayer slow downer | free, browser | 50% to 100% | yes, drag on the waveform | yes, six stems | yes, export at the set speed |
All four keep the pitch, because all four time-stretch rather than resample. The difference that matters for practice is the last two columns.
What each percentage means in beats per minute
A slow downer shows a percentage; a metronome and a chart show beats per minute. The table converts one into the other for five common song tempos, and gives the length of one beat at the slower speed. One bar of 4/4 is four times the beat.
| Speed | 90 BPM | 100 BPM | 120 BPM | 140 BPM | 160 BPM | One beat at 120 BPM |
|---|---|---|---|---|---|---|
| 100% | 90 | 100 | 120 | 140 | 160 | 500 ms |
| 95% | 85.5 | 95 | 114 | 133 | 152 | 526 ms |
| 90% | 81 | 90 | 108 | 126 | 144 | 556 ms |
| 85% | 76.5 | 85 | 102 | 119 | 136 | 588 ms |
| 75% | 67.5 | 75 | 90 | 105 | 120 | 667 ms |
| 70% | 63 | 70 | 84 | 98 | 112 | 714 ms |
| 60% | 54 | 60 | 72 | 84 | 96 | 833 ms |
| 50% | 45 | 50 | 60 | 70 | 80 | 1 000 ms |
The presets on the slow down music page are 50% and 75%, with any value in between. YouTube's player steps through 0.25, 0.5, 0.75 and 1. Amazing Slow Downer's range is 20% to 200%, so it also doubles as a speed-up tool.
How many repeats a loop gives you
A two-bar loop at 120 BPM lasts four seconds at full speed and 5.3 seconds at 75%. The table counts the repetitions in one minute of practice for the loop lengths the tools offer, at three speeds, for a song at 120 BPM in 4/4.
| Loop | Length at 100% | Repeats per minute at 100% | at 75% | at 50% |
|---|---|---|---|---|
| 1 bar | 2 s | 30 | 22 | 15 |
| 2 bars | 4 s | 15 | 11 | 7 |
| 4 bars | 8 s | 7 | 5 | 3 |
| 8 bars | 16 s | 3 | 2 | 1 |
| 16 bars | 32 s | 1 | 1 | 0 |
On the slow downer page the loop is set by dragging across the waveform, and the speed applies inside the loop the same as outside it.
Which stem holds which instrument
The six stems come from Hybrid Transformer Demucs, the separation model Meta's research group published in 2022, in its six-source version: vocals, drums, bass, guitar, piano and other. The model's own documentation notes that the piano source is the weakest of the six. Where an instrument lands decides what can be muted or soloed at the slower speed.
| Instrument on the record | Stem it lands in | Noted in the model's documentation |
|---|---|---|
| lead and backing vocals | vocals | harmony vocals share the stem with the lead |
| kick, snare, cymbals, percussion | drums | |
| bass guitar, synth bass | bass | the kick drum's low end can bleed in |
| electric and acoustic guitar | guitar | added in the six-source model; distorted rhythm parts can share with other |
| piano, electric piano | piano | added in the six-source model; the weakest source |
| synths, strings, pads, brass, everything else | other |
The separation is the one described on the free stem splitter page: six stems, a few minutes per song, in the browser. Muting the stem of the part being learned leaves the rest of the band at practice tempo; soloing it leaves the part alone, slower, for writing it down.
What slowing does to the sound
A time-stretcher repeats short frames of audio to fill the longer duration. SoundTouch, the library on this site and in Audacity, works with a default sequence of 82 milliseconds, a seek window of 28 milliseconds and an overlap of 12 milliseconds. Anything shorter than a frame is repeated whole: at 50% a snare hit is played twice in a row and a crash cymbal turns into a wash, while a held note, a bass line or a sung vowel passes through unchanged in pitch. The Audacity manual says the same of its own Pitch and Tempo effects: "Small corrections are usually clean; anything drastic is a creative effect rather than a repair." With the drums muted, the loudest transients are out of the mix before the stretch, which is why a stem player at 60% sounds cleaner than a whole mix at 60%.
From the practice room to the gig
The count-in before beat one, baked into the same file, is what CountIn, the sibling tool, adds once the song is learned; it can also move the song to another key with the tempo left at 100%.
Frequently asked questions
How do I slow down a song without changing the pitch?
With a time-stretching tool: YouTube's Playback speed menu, Audacity's Change Tempo effect, Amazing Slow Downer, Transcribe!, or the slow downer on this site. A turntable or a tape deck slowed to 75% would also drop the pitch by about five semitones; these do not.
What speed is 75% in BPM?
Three quarters of the song's tempo: 90 BPM for a song at 120, 105 for a song at 140. The table above covers 50% to 95% for five tempos.
Can I slow down one instrument only?
With stems, yes. Each of the six stems has its own mute and solo, and the speed applies to all of them together, so a soloed bass stem plays at 60% on its own and a muted guitar stem leaves the rest of the band at 60%.
Does slowing down lower the quality?
The pitch is unchanged. Short sounds are repeated by the stretch, so drums soften and cymbals smear, more so below 70%; long notes, bass lines and vocals stay clear. The numbers behind this are in the section on what slowing does to the sound.
Can I save the slowed version?
On this site the export renders the mix at the speed set on the slider, as a WAV. Audacity exports a file after Change Tempo. YouTube's speed setting applies to playback only.
Sources
- Seventh String Software, Transcribe! History (versions 1 to 6).
- Roni Music, Amazing Slow Downer product pages (copyright 1997; range 20% to 200%).
- Audacity Manual, Pitch and Tempo (2026).
- Olli Parviainen, SoundTouch Audio Processing Library, 2001 to 2024: default sequence, seek window and overlap values.
- S. Rouard, F. Massa, A. Défossez, Hybrid Transformers for Music Source Separation, Meta AI, 2022; Demucs repository notes on the six-source model.