Digital Filters

Any medium through which a signal passes may be regarded as a filter.
Typically however, a filter is viewed as something which modifies the signal in some way. Examples include:
- stereo speakers
- our vocal tract
- our musical instruments
A digital filter is a formula for going from one digital signal to another.

**Figure 1:** A black box filter.
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``Mus 270a: Introduction to Digital Filters'' by Tamara Smyth, Department of Music, University of California, San Diego.