The Moving Sweeper

The street sweeper produces a distinctive recurring sound. Its movement across the square becomes audible as it approaches and recedes, making the spatial dimension of the place perceptible. The machine produces a sinusoidal tone centred approximately on D, combined with the broadband noise of the rotating brushes. As it approaches, the sound becomes louder and denser; as it moves away, it recedes. The sounds of playing children remain audible but are repeatedly masked by the sweeper.