Tamal Krishna Goswami: It was wonderful to watch Prabhupada record bhajans. He would play the harmonium, and I’d gently play the kartals and try to keep the rhythm because there was no mridanga. Then Prabhupada would put on headphones and, while listening to the recording with the harmonium and kartals, he’d play the mridanga. On a lot of the taped bhajans, Prabhupada is playing both the harmonium and the mridanga. Prabhupada was an expert musician. When the recording engineer heard the chanting that Prabhupada did on the “Happening” album, the first Hare Krishna album, he said that Prabhupada had perfect pitch. He was very impressed with Prabhupada’s voice.
Source: Remembrances by Sidhanta Das – Folio Vedabase