Any linear time-invariant system bounded in reality has a frequency response that will drop off in magnitude before reaching infinity. An ideal triangular wave

Any linear time-invariant system bounded in reality has a frequency response that will drop off in magnitude before reaching infinity. An ideal triangular wave is an infinite sum of sine harmonics because of the discontinuity in its derivative. More generally, the order of the derivative in which the discontinuity happens relates to decay rate of the harmonics. A square wave decays as sinc(f) whereas a triangular wave decays as sinc^2(f).