Halm

Acknowledgements

Halm is built on the work of others. This page lists the third-party source, binaries, and on-device voice models that Halm vendors, bundles, ships, or downloads, together with their licenses.

For questions about any attribution here, email support@halm.app.

espeak-ng

Halm bundles espeak-ng (the eSpeak NG speech synthesizer's phonemization / espeak-ng-data text-analysis data) as the grapheme-to-phoneme front end for the on-device Piper neural voices.

Written offer of source. In accordance with GPL-3.0, the complete corresponding source code for the espeak-ng version used by this app is available at https://github.com/espeak-ng/espeak-ng. On request we will also provide the exact corresponding source for the build we ship; contact support@halm.app.

sherpa-onnx

Halm uses sherpa-onnx (k2-fsa) as the on-device neural-TTS inference runtime that drives the Piper VITS voices.

ONNX Runtime

Halm links ONNX Runtime, the cross-platform ML inference engine that sherpa-onnx executes the voice models on.

Piper voices — "Amy" and "Alan"

The downloadable neural voices Amy (en_US-amy-medium) and Alan (en_GB-alan-medium) are Piper VITS voice models from the Piper / rhasspy sample set.

Attribution & ShareAlike. These voice models are used under CC-BY-SA 4.0. Credit is given to the Piper / rhasspy project and the original voice-dataset authors. As required by the ShareAlike term, any adaptation or redistribution of these models is licensed under the same CC-BY-SA 4.0 license.

SwipeCardsKit

Part of Halm's swipe-card UI is adapted from SwipeCardsKit, vendored and reworked for Halm.

Piper voices — Thorsten, Eva, Joe and Cori

Beyond Amy and Alan above, the shipped on-device voice roster consists of these Piper VITS voice models (upstream: Piper — https://github.com/rhasspy/piper · Piper voices — https://github.com/rhasspy/piper-voices):

Learning data sources

Halm's bundled learning data (word frequencies, CEFR level labels, example sentences, and the vocabulary calibration test) derives from these public sources:

Swift packages

Halm also uses the following open-source Swift packages, each under its own license (MIT unless noted):