Complex sentence: Historically, strings were made of gut, which is still a preferred material today; however, metal strings have become common in the twentieth century, especially for the heavier drone strings or for lower melody strings if octave tuning is used.
Split into simpler sentences: Historically, strings were made of gut, which is still a preferred material today. However, metal strings have become common in the twentieth century, especially for the heavier drone strings or for lower melody strings if octave tuning is used.