A big help to that is in the casting, as here we have Mark Ruffalo as a down on his luck, alcoholic, washed out music producer named Dan who was once at the top of the industry but hasn't signed anyone in over seven years. Ruffalo has this unabashed, scruffy charm that you just can't scrub off of him, and he excels at these kinds of characters because that natural, ragged authenticity just can't help but shine through. He's also got an estranged wife and teenage daughter (Catherine Keener and Hailee Steinfeld) and even though he's a total screw-up we're immediately drawn to him simply because he's Mark Ruffalo, and he is a talented producer who's just been unlucky lately. His luck's about to change though, because in the movie's first scene he comes across a mild singer-songwriter in a club one night, performing a soft folk song in front of a crowd of distracted patrons, and his producer's mind immediately starts working overtime as he catches on to her style and imagines the song in his head, arranged with the background instruments playing themselves to accompany and bolster her sound. It's a magical musical moment, one that sets the tone for the optimistic arc the story will take.
Keira Knightley is Greta, the singer (yes, she did her own singing!), and she's also at a down moment in her life, having come to New York City with her boyfriend Dave (Adam Levine), with whom she worked as his songwriting partner, but who's now made it big from having his own music featured in a film, and quickly falls in love with the rock world that opens up for him from becoming successful. As a result of that, Dave reveals himself to be kind of a tool (most obviously represented by his growing a beard "as big as neck," as one character notes) and dumps Greta for a floozy, leaving her stranded in New York, sleeping on the couch of her pal from back home (James Corden). When Corden talks her into performing that fateful night, she gives a quiet, un-showy performance but of course it's a showstopper for Dan, who accosts her with his personality and offers her a chance to record a demo. The chemistry between Ruffalo and Knightley is wonderful and the rapport that develops between them over their shared love of music makes this film into an old-fashioned semi-romantic comedy of the kind Hollywood really doesn't make anymore. The two set out on their goal of recording an album on the streets of the city with no studio behind them in order to get the authenticity of the real life hustle and bustle. The shooting on location in and around the various clubs and corners of New York make it a summer love letter to the city in the best possible way- one of my favorite scenes is when Dan and Greta share a headphone splitter as they stroll through the streets at night and share each other's playlists.