There's always been the track artist that dances more than they sing, but lately I've been noticing more and more artists that rely heavily on tracks for more than a drum loop, or backing strings or sounds.
I was at a show a few weeks ago, and I knew going in that the band would be playing live to tracks. A singer, two guitar players, but everything else was tracks. I got a peek at the console, and this show was no joke. I was expecting a few mic inputs, and a MP3 player. I was wrong. The band travels with a full blown Pro Tools rig, and breaks everything out and sends it to FOH and monitors. Drums and loops, bass tracks, several keys and synth tracks, and several live and I think some boxed guitar inputs. 3 people on stage, but I think 22 inputs when you factored in the Pro Tools rig. What a great set up, and ability to really nail a mix that's mostly tracks.
I think the key with nailing any track mix, whether it's the solo artist with the MP3 player, or a larger situation, with multiple track inputs, is making the vocals sound like they are part of the track. This of course means the vocalist needs to be on pitch and time, but for the engineer, it means that the vocal needs to be treated as close to studio like as possible. All the EQ and tones and effects of the track are going to be perfect, so the EQ, tone, and effects of the vocal need to be perfect also. Make the audience think that the whole thing is a track. That would be the ultimate compliment, if someone asks you if the live track artist is lip syncing.
Pay attention to the dynamics of the track. You won't be fighting to get the vocal over the track like you would a live band, but the track is going to have more dynamic range, so if it gets quiet, it gets really quiet. Keep your finger on that vocal fader, to ride the level to match the dynamic of the track. There's nothing worse than a vocal sitting on a mix 16dB hotter than everything else.
I know the track artist isn't as fun as a 30 input prog rock band to mix, but don't forget the little details that can take a stock performance and mix to the next level, and get you recognized for a job well done. Who knows, maybe when that track artist gets a real band, you'll get the call to mix them too. Have fun, stay safe.