外差频率 meaning in English

heterodyne frequency

After discussing this kind of filter in this paper in detail , the grads algorithm in time domain and frequency domain is set up when the change of frequency is slow , so it means the algorithm only process the narrowband interference what it changes slowly
论文对数字自适应外差滤波器进行了详细的研究，建立了自适应外差滤波器的时域和频域的梯度算法，该算法的推导使用了外差频率变化缓慢的假设，这意味着该滤波器只能够处理慢变的窄带干扰。