Downloaded a pack full of .flac files and the SP-404 MkII won’t take them? The direct SD-card import doesn’t accept FLAC at all. Here’s the fix.
Not on SD-card import. The direct SD-card path accepts only 16-bit linear WAV/AIFF/MP3. FLAC is a compressed container, so it’s rejected with “Unsupported File.”
The official SP-404MK2 desktop app does read FLAC (and M4A) and down-converts on its own, but it’s built around project transfer, not batch-prepping arbitrary packs. For a folder of loose FLAC samples, converting to WAV first is simpler and works with either import path.
FLAC is a lossless format, so decoding it to 16-bit linear PCM WAV preserves the audio exactly. You’re only swapping the container for one the SP-404 accepts. No quality is lost in the conversion.
| Codec | Linear PCM WAV (from FLAC) |
| Bit depth | 16-bit |
| Sample rate | 48 kHz (or 44.1 kHz) |
| Channels | Mono / stereo preserved |
By hand: ffmpeg -i in.flac -c:a pcm_s16le -ar 48000 out.wav per file,
or decode in a DAW/audio editor. Works, but slow across a big pack.
The fast way: It’s 404, yo! converts a whole folder of FLAC (mixed with WAV, AIFF, MP3, M4A) to SP-404-ready 16-bit WAV in one drag, resampling odd rates and preserving your folder structure. Native macOS, fully offline.
Related: Why the SP-404 says “Unsupported File” · Convert 32-bit float WAV for the SP-404