Scenario Ace Step

Scenario ACE-Step Music

Overview

ACE-Step 1.5, a music production family on Scenario, splits every mode into its own model: Text to Music, Cover, and Repaint each in a Turbo and a Quality lane, plus a full-quality edit trio (Add Layer, Complete Track, Stem Extract), nine members at authoring time. Discover them with search, pick the member by mode name, and treat model_schema_get as the contract.

Connection and the core loop: see the scenario skill in this repo; model-agnostic audio work: the scenario-audio skill. If a sibling skill named here is missing from your available skills, ask the user to install it (npx skills add scenario-labs/skills --skill <name>); unattended, proceed from tool schemas and flag the gap.

Quick reference

Numbers are at authoring time: read caps off model_schema_get. Stem fields take one of twelve fixed values (vocals, backing_vocals, drums, bass, guitar, keyboard, percussion, strings, synth, fx, brass, woodwinds), never free text. srcAudio is a single audio asset: upload_asset first, or reuse a generated asset id. Across members: numOutputs (1 to 4) multiplies cost, thinking (default true, absent on Stem Extract) runs a planning pass, vocalLanguage, where present, defaults to auto-detect. guidanceScale exists on the edit trio alone, audioCoverStrength on Cover alone, and repaintingEnd: -1 runs to the end of the track.

Lane choice

Turbo and Quality siblings take the same parameters, except audioFormat (mp3, wav, flac), at authoring time on Repaint Turbo alone. No member of the family exposed a seed, so two repaints of the same window are two takes, and the singer can change between them. Repaint regenerates the window; do not assume it preserves the source voice. Batch with numOutputs and pick, rather than re-running for a match, and read the next section before repainting to fix a sung line. The asymmetry runs the other way on some section composers in other families, which take a seed and no numOutputs; scenario-audio carries that rule. Quality is the full-size checkpoint tuned for fidelity and prompt adherence; Turbo is distilled for speed and at authoring time costs half as much. Iterate on Turbo (lyrics, structure, windows), then re-run the keeper's parameters on the Quality sibling. The edit trio has no Turbo lane. duration and numOutputs both move the price, so dry_run=true before a long track or a batch.

Writing the song

Keep prompt to a one-line style caption (genre, mood, instruments, production) and put the words in lyrics, shaped with section tags: [Verse], [Chorus], direction inside the tag like [Bridge - whispered], backing vocals in (parentheses), UPPERCASE for belted lines. Vocal-free music is instrumental: true, not "no vocals" in the caption. Tempo and key have dedicated fields (bpm, keyscale, e.g. "C Major"), not caption text.

Editing without regenerating

• Cover keeps the structure recognizable; audioCoverStrength: near 1 stays faithful to the arrangement, 0.5 to 0.6 transforms the genre while the hook survives, around 0.2 borrows only the mood. referenceAudio optionally donates genre and feel; rewritten words go in lyrics.
• For a lyric correction where the source voice matters (a flubbed line, a name that must change), try Cover: srcAudio the whole take, lyrics the corrected sheet, audioCoverStrength at the default 1, numOutputs up to 4 for takes to pick from. High strength favors the source, but does not guarantee the corrected words, singer, delivery, or timing. Waveform differences alone prove neither a voice change nor an audible splice. Audition the candidates against the master and locate the replacement boundaries in both recordings before editing. If listening is unavailable or no candidate matches, deliver the candidates for review and leave the master unchanged. After verification, keep only the corrected span: cut it out of the chosen take with model_scenario-audio-cut (a fixed first-party id, Scenario's single deterministic audio trimmer, so discovery would only re-derive it), asset_download it and the master, and splice it in locally. No MCP tool joins two audio files, so the join is editing work on the downloaded files, not a gap to bridge with another run; when the track rides a video, the compositor in scenario-video-assembly lays the span over the clip as an audio layer instead.
• To change sung lyrics in a Repaint window when a new take of that section is acceptable: start prompt with "Repaint the selected section with new sung lyrics:", pass the full lyric sheet in lyrics with the new section in place, and set thinking: false. Expect the section's voice to be a new take.
• Complete Track works best on a source with clear melody and rhythm.