v1.2.0

The StableStep release. Two flagship features: StableStep, a Stable Audio 3-powered instrumental refiner that finally kills VAE fizz at the source, and MIDI Studio, audio-to-MIDI transcription running on our own native GGML port of MuScriptor. Plus timestep-gated adapters, parameter profiles, two new MDMAchine plugins, and a stack of fixes.

✨ StableStep — Stable Audio 3 instrumental refining

Generated tracks carry a characteristic high-frequency "fizz" from the ACE-Step autoencoder. StableStep re-renders the instrumental through Stable Audio 3 (SDEdit-style partial re-noising, 8-step distilled rectified flow) so the fizz band is regenerated with real spectral detail instead of filtered. Vocals are never touched: BS-RoFormer splits them out (lead and backing), PP-VAE polishes them, and they're remixed over the refined instrumental — the exact complement split guarantees nothing is lost, and lyrics stay bit-identical.

One toggle + a strength slider (0.10–0.60) in Post-Processing. The refine prompt is derived from each track's own caption automatically (vocal descriptors stripped).
Runs natively in the C++ engine — no Python. Two backends, selectable in-app:
- GGML (4 GGUF files, ~5.8 GB): CUDA, Vulkan, and CPU. The fastest option on NVIDIA in our testing — ~2 s of compute for a 30 s clip on an RTX 5090.
- ONNX Runtime / TensorRT (~12 GB): NVIDIA alternative path.
Numerically validated end to end: every ported component matches the reference implementation at cosine > 0.9998; the two backends agree with each other at 0.9999.
Model Manager → StableStep tab downloads either backend set from scragnog/HOT-Step-CPP-StableStep, with license acceptance built in (Stability AI Community License — free for individuals and orgs under $1M revenue). Powered by Stability AI.
New engine surface for tinkerers: POST /sa3-refine (strength/steps/sampler/backend) and SuperSep level=4 — a dedicated vocals+instrumental split.

🎼 MIDI Studio — audio-to-MIDI on the native engine (#80)

Transcribe any library track or uploaded WAV/MP3 into multi-track MIDI (34 instrument groups + drums) using MuScriptor (Kyutai & Mirelo) — ported phase by phase to our own C++/GGML ace-midi engine and validated byte-exact against the reference implementation. A 3.5-minute track transcribes in ~50 s on an RTX 5090; no Python anywhere.

Live piano roll fills in while transcription runs, with per-channel instrument coloring; crossfade playback slider between the original audio and the MIDI rendition, plus per-instrument mute/solo.
Three model sizes (small 103M / medium 307M / large 1.4B) with in-app gated-weight download flow (weights are CC BY-NC 4.0 — non-commercial).
Engine work along the way: exact-parity mel frontend + KV-cache greedy decode, F16 KV cache to fix CUDA decode corruption, byte-exact event decode + MIDI writer.
ace-midi ships in every platform bundle.

🎛 Adapter system

Timestep-dependent adapter gating (interval experts / MoE) — restrict any stacked adapter to a step window, e.g. one adapter shapes structure early, another handles detail late. UI windows are evaluated per step (not raw t), and they now compose correctly with Adapter VRAM quant (previously a silent 32 GB blowup).
PEFT DoRA support + per-module alpha_pattern.
runtime_lowrank mode — factor-apply without materialized deltas: the lowest-VRAM way to run big adapter stacks.
Merge (low VRAM) — opt-in requant of merged weights back to the base's native quant type (~¼ merged-DiT VRAM on a Q8 base).
LoKr Kronecker-apply self-test (HOTSTEP_KRON_TEST); gain_domain parse fix.

📋 Parameter profiles

Save, apply, and delete named full-state snapshots of your generation parameters — in-app, with JSON import/export, inline rename, and click-to-inspect.

🔌 Plugins (MDMAchine)

MD HT Scheduler V3 and MD Trajectory Anchor V5, with user manuals.
Max inference steps raised 200 → 300 (UI + engine clamp).

🔧 Fixes & polish

Storm streaming: stream died instantly (premature close on body consumption); "Keep DiT & VAE loaded" is now honored between stream slots.
In-app restart was dead on Windows (ping-as-sleep hang meant taskkill never fired).
Queue: deleted songs pruned from the persisted queue on load; Nuke All Generations clears the queue store and recent-songs cache.
Logs: GGML debug spam dropped at source with digit-insensitive dedup; terminal stick-to-bottom pin survives layout shifts.
MCP: generating model name appended to song titles.

Models: StableStep sets are on Hugging Face or one click away in the Model Manager. MuScriptor weights are gated (free) — request access via the links inside MIDI Studio.

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