In other words, the tone of the room is essentially applied like a filter to the raw sounds recorded from the artist onstage. This filter, known as impulse response, takes readings from actual physical places, then “synthetically reproduces the sound of a real space like a club or stadium,” said Jake Davis, the lead mix engineer at SeisMic Sound, an audio facility in Nashville that specializes in concert films.
Mixers like Jake and his father, Tom Davis, the SeisMic founder, have a lot of control over the sound in a concert film, and making adjustments is a large part of their job. Some are minor refinements. Others are more like corrections: They make the concert film sound more like what the artist wanted than what necessarily occurred on the night it was filmed. “When you lock something down for a DVD or for streaming or whatever it is, once it’s done, it lives forever,” Tom Davis said. “It never goes away. So you kind of want it to be as good as it can be.”
Mixers can blend parts of a song recorded on one night with parts from another night to create the best combined version. They can fix an errant flat note in a guitar solo by manipulating it in postproduction, or they can ask an artist to rerecord a weak vocal in a studio, layering it into the mix so that it sounds as if it had been delivered live. “We copy, cut and paste, like you do on a word processor,” Davis said. “If there was a little clam in the first chorus, but he did it fine in the second chorus in the same part, we can cut and paste that. We can do vocal maintenance. We can fix a little pitch issue, or bend a note a little bit.”
Although sound mixers record the crowd with a bevy of microphones hidden around the arena, it’s possible — and indeed, common — to exaggerate the sound of that audience, to artificially give the cheering fans some extra kick. “It’s kind of a dirty secret,” Davis said. “But the sound of the real audience is weak. It’s not enough. You end up adding to it, pumping it up. There’s something psychological to hearing other humans having a good time and reacting — it’s like a sitcom and a laugh track.” Jake Davis said that the ideal balance is to “start with the real reaction” and then simply “make it bigger and more obvious.”
Of course, part of the appeal of a live show, even on film, is the impression of reality, and a sense of truth is critical. “The goal of the mix is to enhance the energy of the performance that exists as it went down in the best way possible,” Jake Davis said. “You maintain some element of rawness while taking out things that are distracting, the nuances of a wrong note or a background singer being a little bit off.”