Playing, rendering and recording

PianoFlex can play MIDI files, turn them into audio files, and record what you play.

Playing a MIDI file

A MIDI file (ending in .mid) holds the notes of a piece of music, but no sound. PianoFlex plays those notes on the piano you've chosen.

1. Click Open MIDI…, then Browse for MIDI…, and choose the file.
2. The file starts playing as soon as you choose it. While it plays, the Play button reads Stop: click it to stop, and click Play to play the file again.

The strip beside Play shows how much is playing over the whole file: the taller a bar, the more is sounding there, loud notes counting most. A white line marks where it's playing, and the keys light up as they play. Click or drag on the strip to choose where to start playing from. That point is called the start point, and the file plays from there. A yellow line marks it, and the line under Play shows its time.

You can choose another piano or move any slider while a file plays. The notes that follow play with your change. Notes already sounding ring on for a moment as they were, then fade out.

Rendering a file to audio

Rendering makes an audio file of a MIDI file, played on your piano exactly as you've set it, layers included. The audio file is a FLAC file, which most music players and music programs can open, so you can listen to it or use it in a music project or a video.

1. Open a MIDI file, as above.
2. Click Render to audio.

Rendering works in the background and is faster than playing the file. Click Render to audio again if you want to stop it.

The audio file is saved as a FLAC file (24-bit), in the PianoFlex folder in your Documents, in a folder called recordings. Its name is made of the MIDI file's name and the preset's.

Recording what you play

1. Click Record. PianoFlex is now ready to record.
2. Start playing. Your first note starts the recording.
3. Stop playing. The recording ends by itself once the sound has died away, or, with the fade out ending, 8 seconds after your last note. To end it sooner, click Record: it fades out over 4 seconds (click again to end it at once).

Each recording is saved in the recordings folder in two ways: as an audio file (24-bit FLAC), and as a MIDI file of the notes you played. Both are named with the date, the time and the number of notes, for example 2026-10-18_222533_12_notes.flac.

Notes from ComposerFlex are recorded in the same way as notes from a keyboard.

How loud the files are, and how they end

The Files: button, which shows the level and ending you've chosen (at first "Files: -14 LUFS, fade out…"), lets you choose how loud your audio files are and how they end. The choice applies to both renders and recordings.

• Level:
  • -14 LUFS is the loudness that music streaming services play at. This is the setting PianoFlex starts with.
  • -16 LUFS is a little quieter.
  • peak -1 dB makes the file as loud as it can be without any limiting.
  • engine level leaves the level as the piano itself makes it, with nothing done and no limiting: quiet, with plenty of room above it, and quieter than PianoFlex plays it in the window.
• Ending:
  • fade out ends the file 8 seconds after the last note, fading out over the last 4 seconds.
  • ring out lets the file run until the sound has died away by itself, for two minutes at most after the last note.

After each file, the yellow line tells you how loud it came out.

Sending the notes to another instrument

PianoFlex can send a MIDI file's notes, or ComposerFlex's, to another instrument: a synthesizer connected to your PC, or another program on the same PC. PianoFlex stays silent while it does.

1. Choose where the notes go, once: click the port's name with its ▾ in the MIDI out box, beside the slots, or press Shift+5 (the % key). The list shows everything on your PC that can take MIDI right now: an instrument you've connected, a MIDI interface or a virtual MIDI port, each under its own name.
2. Switch MIDI out on: click the MIDI out box, or press 5. With a MIDI file open, the file's notes go to the port when it plays. With no file open, ComposerFlex's notes go there. What you play goes there too: your MIDI keyboard, the keys on the screen and the pedal bars.
3. Switch it off, to hear PianoFlex again: click the box or press 5 again, or click a slot.

You can switch back and forth as often as you like: the port you chose is used at once, with no list.

• The box shows On or Off (On, live or Off, live when it's ComposerFlex's notes, with no file open), and the name of the port you chose, or None. It shows No file when there's nothing to send.
• PianoFlex remembers the port for next time. If you switch MIDI out on before choosing a port, the list opens so you can choose one. If the port isn't connected, the yellow line says so, and the list opens so you can choose another.
• If your MIDI keyboard comes in on the same port that MIDI out sends to, PianoFlex doesn't send the keyboard's notes to MIDI out, since they would go round and round, and the yellow line says so. You hear the keyboard again when MIDI out is off.
• If no list opens and the yellow line says "No MIDI port to send to on this PC", connect an instrument, or install a virtual MIDI port (below), then try again.
• MIDI out is part of the PianoFlex program. The plugin doesn't have it, since your music program sends its MIDI wherever you choose.

Sending to another program on the same PC

To send the notes to another program, such as REAPER or any other music program, you need a virtual MIDI port. It's a small program, installed separately, that passes MIDI from one program to another. PianoFlex doesn't include one. Either of these two works with PianoFlex on Windows 10 and 11:

• loopMIDI, by Tobias Erichsen, free to download: tobias-erichsen.de/software/loopmidi.html. loopMIDI makes no port by itself. Open it once after installing and click + to make one, called "loopMIDI Port". Its ports exist only while loopMIDI is running, so leave it running, and check that Autostart loopMIDI is ticked in the menu of its icon by the clock. Then the port is there each time Windows starts.
• LoopBe1, by Nerds.de: nerds.de/en/loopbe1.html. Once it's installed, its port, "LoopBe Internal MIDI", is always there, with nothing to set up. Its maker gives it free for personal use. For commercial work, you need to buy a license from their page after 30 days.

Neither one is made by Flex Music Labs. Download them only from their makers' pages above.

Once a virtual port is installed, choose it in the MIDI out list. In your music program, choose the same port as a MIDI input, on the track that should play the notes.