When adding two trigonometric functions of different frequencies, one frequency is drawn inside the other. Like a curve undulating within the envelope formed by another curve, the two functions independently control different parameters of the resulting curve. Although this seems straightforward, a curve inside a curve can get out of control easily. It is highly recommended that if the frequency of a curve is increased by a certain value, its amplitude should be decreased by that same amount. This will maintain the amplitude of the overall curve (the envelope) while independently increasing the frequency of the texture (the inner curve).