3.3. Correcting BPM

Tempo detection is an estimate, and rhythmically ambiguous material can produce a half-time, double-time, or otherwise incorrect result. In the standalone APU Harmonic DJ application, double-click a local track’s BPM cell or open BPM Correction → Correct BPM from its track menu. Enter a value from 40 through 300 BPM. The same menu offers Halve BPM, Double BPM, and Reset to Detected BPM when those actions apply. Half and double use each track’s current BPM, including an existing correction.

To correct a batch, search for bpm:128, press Enter to focus the results, and use Ctrl+A on Windows or Command+A on macOS to select all matching rows. Right-click the selection and choose BPM Correction → Correct BPM to set every selected track to 64, or choose Halve BPM. The menu shows the selection count. All selected tracks must be analyzed local tracks, and half/double actions are disabled if any result would fall outside 40-300 BPM. A batch is saved together; cancellation or an invalid value leaves the whole batch unchanged. Tracks that no longer match the search disappear after the edit completes.

A correction does not overwrite the detector result. The BPM cell identifies a Manual correction, and its tooltip shows both the BPM Harmonic DJ uses and the original detected BPM with its confidence. Resetting removes the correction and immediately returns to the latest detector result.

The corrected value becomes the track’s used BPM everywhere: Library search and sorting, readiness, Mix targeting and generation, Gem Finder, BPM-aware audition playback, saved-Gem evidence, shared collections, and published Mix data. Key and loudness analysis are unchanged.

Corrections are tied to the SHA-256 identity of the complete local file. They survive rescanning unchanged audio, moving an unambiguously matched byte-identical file, removing and later re-adding the same file content, and Library Metadata backup/restore. If any file bytes change-including tag edits or transcoding-the old correction no longer applies, so review the new detector result and correct it again if necessary. Shared collections and published Mixes carry the BPM used for planning, but do not expose the private correction record or stale detector confidence.