As an example, the ideal low-pass filter with impulse response equal to a sinc function is not BIBO stable, because the sinc function does not have a finite L1 norm.
作为一个例子，冲激响应等于Sinc函数的理想低通滤波器不是BIBO稳定的，因为Sinc函数不具有有限的L1范数。