Barbara Arens Piano Vivace - Piano Tranquillo: 15 Sunny Pieces – 15 Relaxing Pieces for Piano. “Piano Vivace – Piano Tranquillo” is the name of the new music book just released by our successful author Barbara Arens. It's a book that's divided in two: turn it upside down and you can start on either side. Grouped around the two basic moods "Vivace" and "Tranquillo," the finely honed pieces range from easy to medium difficulty. There are 15 pieces in each group, no piece longer than two pages.