Gustav Mahler and Das Rheingold - Constant Note

Both pieces have a constant lingering note in the background while the other instruments take their time to enter/crescendo. In the Mahler its a constant high violin while in the Rheingold its a constant bass. Both have no particular rhythm at this specific time to allow each instrument to slowly enter / crescendo. Mahler's has a particular melody as each instrument enters while Rheingold's has an echo, almost like a canon for each instrument as they enter and build up.