MIDI generators: from first idea to finished part

First, understand what MIDI does

MIDI describes a performance: which note starts, when it starts, how long it lasts, and how strongly it is played. It does not contain the sound of a piano, bass, or synthesizer. An instrument turns those instructions into audio. This distinction explains the most common first-session problem: a generator can be working correctly while you hear nothing.

Think of a MIDI clip as an editable score. You can keep the notes and change the sound, keep the rhythm and change the pitches, or remove half the notes to make room for a singer. Exporting audio commits the sound you hear at that moment; keeping the MIDI clip preserves those musical choices for later.

Compare the two creative approaches

Start with the kind of control you enjoy. Both approaches still need your musical judgment.

Riffer’s publisher lists VST3, AU, AAX, and standalone desktop operation; the mobile edition has its own formats. MIDI Agent lists VST3, AU, AAX, and standalone operation, with account, API, or local-model access options. Check the exact edition and access requirements linked below. A plugin license and a third-party service allowance are separate buying decisions.

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Product references: Audiomodern Riffer 4 · MIDI Agent

Set up a small session before generating anything

1. Choose a role for the part

   Write one sentence such as “a sparse bassline under my verse” or “a short melody answering the vocal.” Avoid asking one new tool to create the entire arrangement. Decide which track will play the result and which existing part it must leave space for.

2. Set tempo, meter, and a short loop

   Use your song’s tempo and time signature, then loop four bars. If you are starting from scratch, use the practice session below. Put a simple chord or sustained root note underneath the loop so you can judge the generated part against something musical.

3. Make the instrument work first

   Load a familiar piano or bass sound on an instrument track. Draw one note in the piano roll or play a connected keyboard. Confirm that the instrument produces sound before adding a generator. This separates an audio problem from a MIDI-routing problem.

4. Use the simplest supported transfer method

   For a first session, exporting or dragging a MIDI clip to the instrument track is often easier to diagnose than a live routing chain. Follow the generator’s manual for export. If you use live MIDI output instead, follow your host’s MIDI-input and monitoring instructions; track names differ between DAWs.

Create your first usable musical part

1. Constrain the first attempt

   Use one role, one instrument, a limited range, and a four-bar length. With a sequencer, begin with a modest note density and a known key. With a text tool, specify the same constraints in the prompt. A focused request gives you something easier to evaluate.

2. Generate a few alternatives, then stop

   Keep three promising ideas as separate clips. Name them A, B, and C. Listen to each against the same backing part. Choose the one with the most useful rhythm or shape, even if it needs fewer notes or a different ending. Constant regeneration can hide a small edit that would already solve the problem.

3. Check pitches and range

   Look at the piano roll while listening. Remove notes that clash with the harmony you intend, and move uncomfortable notes into a playable register. Scale membership alone does not establish a good phrase: where a note lands against the chord matters too.

4. Edit rhythm and note lengths

   Shorten notes that overlap the next attack unintentionally. Leave gaps where the vocal or another lead needs attention. Check the last note before the loop returns to the start; a phrase that sounds good once may need a cleaner loop boundary.

5. Shape velocity and accents

   Make the important beats clear without forcing every note to the same velocity. Check how your chosen instrument responds: a velocity change may alter tone as well as level. Use deliberate accents rather than random variation for its own sake.

6. Commit the keeper and save the source

   Copy the selected MIDI clip into your arrangement and keep the original on a muted track or in a clearly named folder. Save the generator preset or prompt alongside it. You can now make musical decisions without losing the starting point.

Practice: build a four-bar idea into eight bars

Create a 4/4 session at 100 BPM. Use C minor for this exercise. The downloadable practice file contains original YRS MIDI bass and chord parts, with one bar each of C minor, A-flat major, F minor, and G minor. Assign the tracks to suitable instruments after importing. This is a teaching clip, not output claimed to come from either featured plugin.

Keep the chord part as a reference and create a new bass or melody above it. Compare your generated idea with the reference instead of stacking both basslines. If your DAW labels middle C differently, use MIDI note numbers when comparing registers; octave-name conventions vary.

Example prompt: Create a four-bar monophonic bass part in C minor at 100 BPM, in 4/4. Use a low register, leave space on beat four, and finish with a phrase that can return to C. Return editable MIDI.

Duplicate your chosen four bars. Change only the final bar of the second copy: leave a larger gap, simplify the rhythm, or change the approach to the first note of the next section. Listen to the full eight bars with the chords. Keep a change only if it improves the phrase in context. The prompt is an example of useful constraints, not a promise that a model will follow every instruction exactly.

Troubleshoot the signal path

If a file plays correctly after export but live output does not, the musical data is probably usable; concentrate on the host’s live MIDI route. If both methods fail, test a known MIDI file on the destination instrument. Change one part of the chain at a time and save the last working setup.

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Finish a part, rather than collecting variations

Listen with the rest of the song at a normal working level. Mute the generated part for a few bars, then bring it back. Decide what it contributes: movement, a hook, harmonic support, or an answer to another instrument. If it does not have a clear role, simplify it or leave it out.

Before exporting audio, keep an editable MIDI version and note the instrument preset. Check the first and last notes, any sustain-controller messages, and the clip’s relationship to the next section. The success test is a repeatable part that supports your arrangement, not the number of patterns the tool can produce.

Your buying and setup checklist

Work through the list here, or print the guide for your next session.

• I know whether I want rules-based sequencing, text prompting, or both.
• My host accepts the exact desktop plugin format and operating-system version.
• I have checked whether this license is desktop, mobile, an upgrade, or another edition.
• I have an instrument that can play the generated MIDI.
• I understand any separate AI access or ongoing usage costs.
• I can import a clip, hear it, edit it, and save an eight-bar arrangement.