An SFZ instrument is a plain text file that tells a sampler which WAV file to play on which keys. Turning a folder of one-shots into one means finding the pitch of each sample and giving each a range of keys around it. The free WAV to SFZ mapper does both steps in your browser, lets you play the result on a keyboard, and exports a ZIP.
What an SFZ file actually is
SFZ is a text format that points at audio files and sets, for each one, a root note and the lowest and highest key it covers. It is not an audio format, so the samples stay as ordinary WAV files next to the text file. The mapper also writes a DecentSampler preset, which uses the .dspreset format, into the same ZIP.
Keep the samples with the preset when you move the instrument, because the text file only refers to them by name. Neither format is a Kontakt .nki instrument, so check what your sampler can open before you rely on it. A free player such as sforzando opens SFZ.
Root notes and zones
The root note is the key at which a sample plays back at its original pitch. Every other key in that sample's zone plays the sample faster or slower, which changes its pitch. The mapper detects each root note, puts the sample there, and fills the gaps between samples with zones.
A basic sampler changes pitch by changing playback speed, so pitch and length move together. Each semitone is a speed change of 2 to the power of one twelfth, about 1.0595. A 1.000 s sample played 7 semitones above its root runs at 1.498 times speed and lasts only 0.667 s.
How many samples you need
The further a key sits from a sample's root, the more the sound is stretched out of shape, with the tone going thin or muffled and the note length changing. One sample per octave is playable, and one sample every major third, which is 4 semitones, sounds natural to most ears. The table shows the speed change and the resulting length for a 1.000 s sample.
| Distance from root | Speed | Length of a 1.000 s sample |
|---|---|---|
| 1 semitone up | 1.059 | 0.944 s |
| 3 semitones up | 1.189 | 0.841 s |
| 4 semitones up | 1.260 | 0.794 s |
| 7 semitones up | 1.498 | 0.667 s |
| 12 semitones up | 2.000 | 0.500 s |
Even four to six well-spread one-shots make a usable instrument once the zones fill the gaps. The mapper takes up to 24 samples.
Where detection and playback go wrong
Pitch detection is an estimate. Noisy, percussive or layered samples can give a wrong note, including an error of a whole octave, so listen to each sample against its assigned key. If one is wrong, click the sample and choose the correct key to remap it.
Detection only makes sense for samples with a clear pitch, such as keys, bass notes, plucks and stabs. A kick or a snare has no root note to find, so a drum kit belongs on pads rather than a keyboard. For that, use the Chop-to-Kit Builder.
Exporting a preset does not change the rights attached to the samples inside it. If you did not have the right to use the recording, the instrument inherits that problem.
Getting the samples in the first place
Good instrument samples are clean single notes with room to ring out. Song Chopper cuts a track into slices, and the audio reverser can turn a hit into a swell that you map as a pad sound. The related note on reversing audio covers where that goes wrong.
SongChop in the studio can turn a song you upload there into categorized one-shots and beat-aligned loops for your sampling workflow. The folder you used in the free mapper stays in your browser. Free usage has limits, so review the cost before you process a song.
Free tools for this job
Free browser tools that go with this post.
- WAV → SFZ Instrument Mapper (vstchop.com) — Drop one-shots, auto-detect their root notes, play the keyboard, export SFZ + DecentSampler.
- Chop-to-Kit Builder (vstchop.com) — Slice any track into hits, audition on pads, export a labeled kit ZIP.
- Song Chopper (songchop.com) — Split any track into transient-cut slices and download them as WAV or ZIP.
- Audio Reverser (songchop.com) — Reverse a whole track or just a selection — plus a one-tap tape-stop effect.