Digital Filtering

The sub-pages linked from here graphically investigate the frequency-response curves produced by various digital filters implemented within my Sound engine. Most of the pages investigate specific digital filters used in specific modes. However, Cascaded Digital Filters investigates what happens when filters are combined.

All of the graphs on these sub-pages were empirically obtained with a sample rate of 20000 Hz. Each graph was generated by sweeping a tone through a range of frequencies, by processing the result through one or more digital filters, and by extracting a power envelope. Two styles of graph are used to plot frequency responses for specific digital filters:

The digital filters described on this page vary according to the extent to which they employ feedback and feedforward processing, which terms are explained by Victor Lazzarini in section 6.6 of The Audio Programming Book. In a nutshell, feedback employs one or more a previous outputs, while feedforward employs one or more previous inputs. The order of a filter indicates how much sample history is taken into account. For example, a 1st order filter can employ a previous input, a previous output, or one of each.

The digital filters implemented within Sound come from various sources. Credits are provided in each unit's reference entry.

© Charles Ames Page created: 2014-02-20 Last updated: 2015-07-12