 The effect is accompanied by unexpected Neapolitan harmony in the orchestra, with all the violins playing in unison high on the G string to intensify the sound.The first singer to perform the aria onstage was Mozart's sister-in-law Josepha Hofer, who at the time was 32.By all accounts, Hofer had an extraordinary upper register and an agile voice and apparently Mozart, being familiar with Hofer's vocal ability, wrote the two blockbuster arias to showcase it.