Play a recording of the lead vocal and sing along. The purpose of a backing vocal is to support the lead vocal, so it's preferable to use the lead melody as the starting point for composing a backing vocal. If the same melody in a higher or lower octave works best, go with that. There's no need to over-complicate the backing vocals.
Record your backing vocal idea using the voice recorder or "Dictaphone" function on your cell phone, or another simple audio recording device.
Play the lead vocal again and hum a single note. Try to find a single note that sounds good with all of the notes in the melody to use in your harmony backing vocal. Typically harmonies are a major third, or three half-steps above the main melody. Some harmonies are a perfect fifth, or seven half-steps above the main melody. Use a piano to help you locate these notes, if necessary.
Sing along with the melody again, but this time sing in harmony, starting from the note identified when humming. To sing a harmony, sing the same or a very similar melody to the lead, but you start at a higher or lower note. You don't need to stick exactly to the same melodic structure as the lead melody, but don't deviate for the sake of doing so. Harmonies exist to add harmonic depth to the lead vocal.
Record your harmony vocal idea using your cell phone.
Click on the "Send To" button on the first backing vocal channel. Select "Bus 1."Routing to a bus channel lets you control multiple audio with one set of controls. Repeat this process for each backing vocal.
Click on "Bus 1" to highlight it. This assigns the subsequent commands to this channel only, not the entire mix. Slide the "Gain" fader for "Bus 1" up. This increases the volume. Set the backing vocals to approximately 80 percent of the volume of the main vocal.
Click "Effects" and select "Compressor." Adjust the threshold to 80 percent. This reduces the volume of the loudest 20 per cent of the vocals. This makes the vocals louder, but also makes them punchier and tighter, as there are less "spikes." Adjust the compressor "Output Gain" parameter by 20 percent.
Click "Effects" and select reverb. This effect adds ambiance and prolongs the decay of a sound, making the vocals blend better. Tweak the "Depth" and "Time" parameters to suit your taste.
Click "Effects" and select "Auto-tune" or "Pitch Correct." Set the "Tracking" setting high if there are a lot of out-of-tune notes in the recording. Set it low if there are just a handful of out-of-tune notes. Set the "Retune Speed" setting high for a natural-sounding pitch correction effect.