Free online FLAC to SF2 converter

A sampler, MIDI device, or music program that supports SoundFont 2 may require an .sf2 instrument instead of a standalone .flac recording. This is not a simple audio re-encoding: the recording must be imported as a sample and assigned to an instrument zone inside a SoundFont bank.

What the FLAC format is

FLAC is a lossless compressed audio format. It preserves the original PCM audio while reducing file size, so it is common for CD rips, music archiving, sample libraries, and exports from audio tools such as Audacity, Exact Audio Copy, foobar2000, and digital audio workstations.

A FLAC file normally contains a recording, not playable-instrument information. It has no SoundFont key mapping, root-note assignment, velocity layers, loop points, envelope, or MIDI preset definition.

What the SF2 format is

SF2, or SoundFont 2, is a sample-based instrument-bank format used by MIDI synthesizers, software samplers, game-audio systems, and applications such as FluidSynth and MuseScore. An SF2 file can contain PCM samples plus instruments, presets, key and velocity ranges, tuning, filters, envelopes, effects, and loop settings.

Its advantage is that one sample can be mapped across a keyboard and triggered by MIDI rather than played only as a fixed recording. SF2 is appropriate for creating a playable instrument, drum kit, or collection of presets; it is not an alternative container for ordinary stereo music.

How to actually convert FLAC to SF2

Use FFmpeg to decode the FLAC and Polyphone to build the SoundFont. Polyphone is a desktop SoundFont editor; the conversion requires editing instrument metadata because no automatic mapping can infer the intended root note or playable range reliably.

1. Check the source. Use a one-shot, sustained note, drum hit, or other isolated sample if you are building an instrument. A complete stereo song can technically be imported, but it will behave as one long sample rather than a useful keyboard instrument.
2. Decode the file to a SoundFont-compatible WAV sample:

ffmpeg -i input.flac -ac 1 -ar 44100 -sample_fmt s16 sample.wav

-ac 1 makes the sample mono, -ar 44100 sets a broadly compatible sample rate, and -sample_fmt s16 produces 16-bit PCM. Omit or change these options when the target sampler specifically supports stereo, another sample rate, or a different workflow.

3. Open Polyphone, create a new SoundFont, and import sample.wav into its sample list using the sample import command or the sample-list context menu.
4. Create an instrument and add the imported sample to an instrument zone. Set the sample's root key to the note at which it was recorded, then set the key range over which it should play. For example, a sample recorded at C3 normally receives root key C3.
5. For a sustained sound, define loop start and loop end points and enable looping. Set amplitude envelope, tuning, attenuation, and velocity ranges as needed. For a multisample instrument, repeat the import and create separate zones for each recorded note or velocity layer.
6. Create a preset, assign the instrument to it, and set its bank and program number if the receiving MIDI device expects a particular program.
7. Save the project as an editable Polyphone project if desired, then use File → Save as and choose the .sf2 format. Test the resulting bank in Polyphone, FluidSynth, MuseScore, or the target sampler.

You can also convert the file on the 101convert.com website for free without installing software, where the available conversion workflow supports this format pair.

Quality, compatibility, and limitations

FLAC decoding itself is lossless; quality changes occur only when you resample, reduce bit depth, convert stereo to mono, or edit the sample. SF2 stores sample data and synthesis parameters, not the original FLAC compression, so the resulting file is usually larger than the source sample.

A single FLAC produces only a basic one-sample instrument unless you manually add key ranges, loops, envelopes, and additional samples. Transposing one sample across a wide keyboard changes its duration and timbre; multisampling produces better results.

SoundFont compatibility varies. Older synthesizers commonly expect 16-bit PCM, mono samples, valid loop boundaries, and conservative sample rates. Extremely long samples, unusual rates, malformed loop points, or unsupported modulators may fail or sound differently in another player. Keep the original FLAC because the SF2 build may involve irreversible downmixing, resampling, trimming, and loop edits.