Behind many expressive instruments is a quiet piece of infrastructure: sample conversion. ConvertWithMoss, the free open-source tool by Jürgen Moßgraber, reached version 20.3 on September 22, 2026. As Synth Anatomy reports, the release adds support for Sequential Prophet X/XL and classic E-mu Emulator formats. It is not an MPE tool by itself, but it matters for anyone who builds or migrates sampled instruments for expressive playing.
What ConvertWithMoss does
ConvertWithMoss converts multi-sample files between formats used by hardware samplers and software instruments. It runs as a standalone application on macOS, Linux and Windows, and it is completely free. You can find the project and its documentation on mossgrabers.de, and the source on GitHub.
The idea is simple: you point it at a library in one format, choose a target format, and it rebuilds the instrument with its key ranges, velocity layers and loops.
What is new in 20.3
Version 20.3 focuses on hardware and vintage formats:
- Sequential Prophet X/XL sample formats (GRP/ZIP), with read and write support
- Compatibility with the original 1981 E-mu Emulator and its formats (HFE, EMUFD, IMG)
- Extended E-mu Emax and Emax II support across many formats (EM1, EB1, EM2, EM1FD, EM2FD, EZ1, EZ2, IMG, ISO, HFE)
- Assorted bug fixes and improvements
Versions 20.0 to 20.2 were released through the summer, steadily expanding hardware compatibility, so the project is clearly active.
Why this matters to MPE players
Modern samplers increasingly add per-note expression. One recent example is Audiomodern's Soundbox 1.3, which added MPE support and integrates ConvertWithMoss for bringing in libraries from other formats. A converter closes the gap between the enormous body of existing sample content and the new instruments that can play it expressively.
Consider what that unlocks:
- Reviving classic sounds. A vintage sampler library can be reborn on an MPE-capable engine, where pressure and slide can shape it in ways the original hardware never allowed.
- Reducing lock-in. Converting between formats lets you move your instruments to whichever platform best suits your controller.
- Testing ideas quickly. Sound designers can try one library across several samplers to compare expressive behavior.
A practical workflow
If you want to prepare a sampled instrument for expressive playing, this is a sensible path:
- Convert the library with ConvertWithMoss into the format your MPE-capable sampler reads.
- Check the mapping. Verify key ranges, loops and velocity layers after conversion.
- Map expression. In the target instrument, assign pressure to volume or filter and slide to brightness or another timbre control.
- Set the pitch bend range so it matches your controller's MPE settings.
- Play and refine. Sustained sounds, strings, pads and winds usually respond best to expressive gestures.
Expect to review the results
Conversion is rarely perfect. Different formats handle loops, envelopes and layering in different ways, so features can be approximated or dropped. Treat the converted instrument as a starting point and audit it by ear. Make sure you also have the right to convert and use any library you work with, since licensing terms vary by publisher.
The bigger picture
The MPE ecosystem depends as much on content and tooling as on controllers. Open-source utilities like ConvertWithMoss lower the barrier for sound designers and small developers, helping expressive instruments reach a wider audience. Version 20.3 is a reminder that some of the most useful tools in a musician's kit are free, community-driven and quietly maintained.