AI music BPM control: set the tempo in the prompt

You control the BPM of AI-generated music by writing it into the prompt, as a number: "72 BPM" or "142 BPM half-time". Neither Sume's music API nor Google's Lyria 3.5 documents a tempo parameter; Sume's docs say the request has no seed, temperature, guidance or duration field, and the tempo is a creative direction, not a guaranteed setting.

Sume's guidance is from the Music 1.0 and Music Router docs. Google's Lyria page says to mention instruments, BPM, key and mood, and its Flow Music post lists easier tempo control as a Lyria 3.5 gain. Read 2026-09-29.

How do I write the tempo?

Give a number and a feel, and pair it with a key and lead instruments, as the Music 1.0 brief does. One line of the docs' example: "Hushed and slightly melancholic neo-soul nocturne, 72 BPM, D minor."

curl -X POST https://api.sume.com/v1/music-router/generate \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: bpm-128-001" \
  -d '{
    "prompt": "Driving synthwave, 128 BPM, F minor. Pulsing bass, gated snare, bright arpeggio. A 1-minute track. Instrumental, no vocals."
  }'

Will the track hit that exact BPM?

Not guaranteed. Sume's docs call the brief axes "creative directions, not guaranteed output settings" and tell you to verify the generated audio. They also note that a lyrics field, when present, is model-reported metadata and not an audio measurement, so do not read tempo off it. Measure the track in an audio editor or a BPM tool and regenerate if it is off.

How do I keep several tracks in the same tempo?

Repeat the number and the key in each brief, and change the arc. For contrasting scenes, the docs go the other way: vary the tempo by at least 12 BPM, the genre family and the lead instrument.

Can I change the tempo after the track exists?

Not through Sume's music API, and Google says Lyria music generation is single-turn: refining a result with more prompts is not supported. Generate a new take with a changed number in the prompt. Each take is billed as its own generation.