1 · MIDI output

Looking for MIDI ports…

2 · Reaper

1. Options > Preferences > Audio > MIDI Inputs. Enable input on your virtual port. Older Reapers list it under MIDI Devices.
2. Insert > Virtual instrument on new track. Pick a synth.
3. Right-click the track's record arm button. Input: MIDI > your port > All channels.
4. Press Send test note above. The synth should sound.
5. Record in Reaper. Sing here.

Other DAWs work the same. Enable the port as a MIDI input and arm a track.

Notes land about a tenth of a second after you sing them. Nudge the recorded items back in Reaper, or record in the full app for corrected timing.

Keep this tab open. It keeps sending while Reaper has focus.

3 · Sing

Wear headphones. Separate repeated notes with a consonant: ta ta ta.

4 · Detection

Push Gate up if room noise triggers notes. Push New-note distance up if vibrato splits notes.

Pitch bend sends your exact pitch between semitones. Set the synth's bend range to ±2 semitones.