In the period from the end of the 1960s to the middle of the 1970s, advances in technology allowed for the increased power of amplification and sound systems without losing sound quality, thus giving hard rock bands the opportunity to use larger and larger venues. Attributing the birth of arena rock to the Rolling Stones' 1969 US tour, "The Guardian" ranked the tour number 19 on their list of the 50 key events in rock music history. Prior to the tour the loudest sound at big-capacity shows was often the crowd, so the Stones ensured they had lighting and sound systems that would allow them to be seen and heard in the biggest arenas, with "The Guardian" stating their "combination of front-of-house excellence and behind the scenes savvy took the business of touring to an entirely new level."