Control

Speed Control

Speed control from 0.50x to 1.50x: semitone table, BPM and length changes, how it interacts with reverb, bass and tone, and values for slowed or sped up edits.

Open the free editor: upload MP3, WAV, AAC, OGG or FLAC, adjust speed, reverb, bass, tone, width and space, then export MP3 or a ZIP of many tracks. Everything runs in your browser.

Speed is the first control in the chain and the one that defines the edit. Everything else in the slowed reverb maker shapes a sound; Speed decides whether you are making a slowed edit, a sped up edit or neither. The slider runs from 0.50x to 1.50x with a default of 1.00x. This page explains what the slider does to the signal, how rate translates into pitch and tempo, how it changes the behaviour of the other controls, and where to set it for each kind of edit.

What Speed does in signal terms

The editor sets the playback rate of the decoded audio. At 0.85x the samples are read 15% slower than they were recorded, so every event in the song takes longer to happen and every frequency comes out lower. At 1.30x the opposite happens. With Preserve pitch off, which is the default, pitch and tempo are locked together exactly as they are on a turntable or tape machine. Slower is lower. Faster is higher.

That coupling is the sound of the genre. The lower, heavier voice in a slowed edit is the pitch drop. The bright, excited voice in a sped up edit is the pitch rise. If you want to change tempo without changing key, the preserve pitch toggle switches the editor to a time-stretch mode, covered on its own page. Note that the reverse, changing pitch without changing tempo, is not something this editor does. Pitch is tied to speed, so to lower the pitch of a song you slow it down.

Speed also changes the output length. The exported MP3 of a 3:30 song is 4:07 at 0.85x and 2:42 at 1.30x.

Rate to semitones

Pitch is logarithmic, so the relationship between rate and semitones is:

semitones = 12 x log2(rate)

A rate of 2.0x would be exactly 12 semitones, one octave, up. The slider does not go that far, but the formula gives every value in range:

Three values are worth memorising. 0.84x is almost exactly 3 semitones down, 1.19x is 3 up, and 1.26x is 4 up. If you want a slowed version that lands in a real key relative to the original, those are the rates to use.

How Speed interacts with the other controls

Speed sits before every other stage, so changing it changes what the rest of the chain receives.

Reverb and Space. The reverb decay is measured in seconds of output. Slowing the song does not lengthen the tail, but it does lengthen the gaps between notes that the tail has to fill. A 2.4 s decay on a 120 BPM song covers a little over one bar. Slow that song to 0.80x and the same 2.4 s covers less than a bar at the new 96 BPM. The tail feels relatively shorter and the mix can take more reverb before it smears. Conversely, at 1.30x the beats are closer together and the same decay rings across more of them. This is why sped up edits want little or no reverb.

Bass. Slowing moves the kick and bass down in frequency. A kick that sat at 60 Hz is near 51 Hz at 0.85x. Small speakers lose it, which is one reason slowed edits add bass. Speeding up moves it the other way and the low end thins out; a small bass lift helps there too.

Tone. Slowing drags the high end down with everything else, so a bright mix becomes duller before you touch Tone. Slowing also exposes any graininess in the source because every artifact is stretched. A negative Tone hides that. Sped up edits push energy upward and usually want a brighter top to match the energy, as the Lift preset does.

Width. Not affected by Speed in any direct way, though a wider reverb at a slower tempo reads as a bigger space.

Recommended Speed by goal

Within the classic band, 0.85x is the most common single value, and the best speed guide explains how to pick within the range by genre and tempo.

A method for choosing Speed

Do not pick a number and move on. Audition.

1. Load the track and leave Reverb at 0% for now.
2. Play the chorus at 0.90x. Ask whether it already sounds slowed. For fast songs it usually does.
3. Drop to 0.85x. Ask whether the singer still sounds like themselves. For most pop and rap vocals the answer is yes.
4. Drop to 0.80x. Ask whether the words are still crisp. This is where consonants start to soften.
5. Pick the slowest value that passed all three questions. Then add reverb.

For sped up edits, run the same test upward: 1.15x, 1.25x, 1.35x, and stop at the fastest value where the vocal is still a voice rather than a character.

Mistakes with Speed

• Choosing by number instead of by ear. 0.80x is right for one song and wrong for the next. Tempo and vocal register matter more than the rate.
• Changing Speed after setting reverb. Speed changes how the tail sits against the beat. Set Speed first, then dial in Reverb and Space.
• Mixing speeds across an album. A batch posted at four different speeds sounds like four different projects. Pick one and apply it to all selected tracks.
• Slowing a song that is already slow. A 70 BPM ballad at 0.80x is 56 BPM, which has no pulse left. Slow songs often want 0.90x or a different treatment.
• Expecting Preserve pitch to fix everything. Time-stretching below about 0.70x introduces its own warble. Below that, the classic coupled mode often sounds cleaner.
• Slowing a 128 kbps MP3 and blaming the tool. Stretching a low-bitrate file exposes every compression artifact. Use the best source available.

Speed and the export

The exported MP3 reflects whatever Speed you previewed, because the preview and the export run through the same chain with Preserve pitch off. With it on, the export will be pitch-shifted: Preserve pitch changes the live preview only; exported files keep the speed-linked pitch. The file is 96 kbps, 32 kHz, encoded in a web worker in your browser. Slowed material compresses well at that rate because the high-frequency content, where MP3 encoders spend most of their bits, has been shifted down. Sped up material has the opposite profile, so start from a lossless or 320 kbps source when you can. For YouTube, TikTok and Shorts the export is fine either way since those platforms re-encode. For a distribution master, use a WAV source in a DAW.