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Section 2Rus

Tempo-map synchronization when processing drums only (Drums Only)

Example files: Drums MIDI (drums-only result)

When converting in Drums Only mode (the "My file contains only drums" checkbox is ticked), the service returns only a MIDI file (example_drums_only.mid) — without stems. This section is short: its goal is to make sure the drum transcription came out correctly and the MIDI matches your audio exactly. The tempo-map here is taken straight from the MIDI — you can open it and start working.

2.1. Checking MIDI synchronization with the source audio

As in Section 1, we open the MIDI as a new project (don't drag it into an open one!) so Logic takes the tempo-map from the file, then lay the source audio underneath and check the match.

  1. Open example_drums_only.mid → Open With → Logic Pro. A Tempo track with the tempo-map from the file (here ~68 BPM) and a Drums region (Kick = C1) appear in the project.
  2. Drag the source example_drums_only.wav into the project at position 1 1 1 1.
  3. Check that the MIDI notes match the audio hits. The most precise way is to compare the time in milliseconds: place the playhead on the start of the MIDI note, then on the hit's transient in the waveform, and compare the LCD readings.
    • First hit: note 00:28,209 vs transient 00:28,204 → difference ~5 ms.
    • Last hit: note 03:59,090 vs transient 03:59,095 → difference ~5 ms.
    • Hit in the middle: note 02:21,149 vs transient 02:21,151 → difference ~2 ms.

The acceptable difference is within 10 ms (processing rate 100 FPS). As you can see, the synchronization stays within these limits along the whole length of the track. The transcription is correct — you can practice to it, and the tempo-map is already embedded in the MIDI.

2.2. Tempo-map mismatch with the target project

A separate task is to insert the produced drums-MIDI not into its own tempo-map, but into an already existing project with its own grid. Here, simply matching the source audio is no longer enough.

Example: in a finished project the full mix and drums sit at a constant 136 BPM. But DrumsMIDI calculated a tempo-map around ~68 BPM (exactly half, and fluctuating). The tempo-maps are different — if you just drag the drums-MIDI into such a project, the notes won't land on the grid and will drift apart.

To re-grid the drums-MIDI from its native tempo-map onto your project's tempo-map, the Adjust Tempo-Map utility is used — that's covered in the next section.