"Barney and the Choir" is a charming and amusing episode, but I will have to go with the reviewers who have found it a bit too implausible, especially from a musicianly point of view. Singing is not an all-or-nothing matter, and someone could easily have taken Barney aside and explained to him kindly and diplomatically that they would coach him on his pitch and voice production later, but for the impending concert they would have to get someone else. Who knows how Barney would have reacted, but this would at least have been more true-to-life. In addition, no choir director would accept a new member sight unseen without hearing him sing first. The fourth-season episode "The Song-Festers" is a much superior choir episode, better-written and with more emotional depth. Still, "Barney the Choir" is still quite funny, with the scene of Barney "singing" into the microphone to a deep bass voice (provided by Glenn Cripes) arguably one of the series' classics.
Review of Barney and the Choir
