https://en.wikipedia.org/wiki/The_CowsillsHair -
Following rehearsals at their home, and demo sessions at SIR Studios on Santa Monica Blvd, The Cowsills' version of "Hair" was recorded over two days in early October 1968 at TTG Studios in Hollywood, where the TV company producing the special were regular clients. A key attraction of TTG was its custom-built 16-track recorder, the only such machine available in Los Angeles at the time, which attracted leading rock acts like Jimi Hendrix and Frank Zappa. Working with house engineer Angel Balestier, the track was arranged and produced by Bob and Bill, who made sure that each member of the group got to contribute an individual vocal part to the recording, both in lead and background vocals, ensuring that each of the group's members would feature on screen when they performed it for the TV special.
Interviewed in 2018, Bob Cowsill recalled the intensive recording process, which was complicated by the fact that the group has not been in a recording studio for several months. The basic rhythm track was laid down first by Bill, Bob, John and Barry, but John (who was only 12 at the time) had difficulty mastering the time changes in the song, especially during the bridge ("Oh say can you see") section, and it reportedly required
over 100 takes to achieve a satisfactory version. The group then proceeded to record the elaborate backing and lead vocal tracks, which were intricately arranged and engineered. The backing vocals were all double-tracked, and Balestier added additional "sparkle" to each vocal pass by sending the signal from the vocal microphone first through a Leslie speaker, then to the TTG echo chamber. The clean vocal signal, the "Leslie-ed" vocal signal and the Leslie-plus-echo signal were then all separately fed back to the console and mixed onto one track of the master. Each section of backing vocal was then double-tracked onto a second track, using the same setup of Leslie and echo, creating a very dense and lush sound. Another notable feature of the arrangement was dictated by the purpose of the recording - the network was concerned that some lyrics in the song might be problematic for viewers in the more socially conservative areas of the United States, so the group omitted the original final verse (which mentions God, Jesus and the Bible) and replaced it with a repeat of the first verse. [6]
Balestier mixed the mono track for the group to use during the filming of the special at the end of the final day of recording, but MGM records had no interest in releasing the song at that time. Bill had an acetate of the song cut at DCT Recorders which ended up being played for a DJ at WLS (AM) in Chicago where it generated significant attention. The TV special was taped on January 5, 1969, in San Francisco. As the air date of March 18 approached, MGM changed their minds and released the single. At this same time Bill and Bob were working on a live album, "The Cowsills in Concert" (released May 3), which included a stereo mix of "Hair" and became the group's best selling album.[6][9] The band had a No.2 US hit and million seller with this version of the title song from the musical Hair.[4]