I remember a while back (maybe 10 years?) NPR spent some airtime trying to address head-on their alleged liberal bias. I respect that, I think their effort was sincere.
What left me frustrated, though, was they never addressed what I saw as their main vector of bias: they seemed to broadcast many more interviews with people unhappy about conservative policies, than people happy with conservative policies.
E.g., illegal immigration was a hot topic at the time. NPR provided a lot of sympathetic interviews with illegal immigrants, both adults and children. I don't think I heard even one NPR interview with individuals in other groups, e.g. construction companies that get out-bid by competitors who pay illegal immigrants under the table, or would-be immigrants who are awaiting their turn to legally enter the U.S.
Again, I don't doubt the integrity of Bob Edwards and other NPR staff who tackled that project. But I think it shows how hard it can be for liberals to accurately understand conservative perspectives.