Frequency Devices, Inc. offers this valuable design guide about analog and digital filters. Many basic principles taught in a signal processing class are discussed, such as sampling a signal, aliasing, and frequency-domain analysis. The equations and parameters that govern filter operation are well explained. The guide defines many of the considerations necessary to choose which type of filter best suits a particular application, and a general procedure to make the correct decision is provided. Most of the information pertains to analog signals and devices, but a good introduction to digital filters is presented as well.