DC Blocker Next  |  Prev  |  Up  |  Top  |  Index  |  JOS Index  |  JOS Pubs  |  JOS Home  |  Search


DC Blocker

The dc blocker is an indispensable tool in digital waveguide modeling and other applications.11.4 It is often needed to remove the dc component of the signal circulating in a delay-line loop. It is also often an important tool in multi-track recording, where dc components in the various tracks can add up and overflow the mix.

The dc blocker is a small recursive filter specified by the difference equation

$\displaystyle y(n) = x(n) - x(n-1) + R\, y(n-1)
$

where $ R$ is a parameter which is typically somewhere between $ 0.9$ and $ 1$ (for a 44.1 kHz sampling rate, $ R=0.995$ is good). The transfer function is

$\displaystyle H(z) = \frac{1-z^{-1}}{1-Rz^{-1}}, \protect$ (11.10)

thus, there is a zero at dc ($ z = 1$) and a pole near dc at $ z=R$. Far away from dc, the pole and zero approximately cancel each other. (Recall the graphical method for determining frequency response magnitude described in Chapter 8.)



Subsections
Next  |  Prev  |  Up  |  Top  |  Index  |  JOS Index  |  JOS Pubs  |  JOS Home  |  Search

[How to cite this work] [Order a printed hardcopy]

``Introduction to Digital Filters with Audio Applications'', by Julius O. Smith III, (August 2006 Edition).
Copyright © 2007-02-02 by Julius O. Smith III
Center for Computer Research in Music and Acoustics (CCRMA),   Stanford University
CCRMA  [Automatic-links disclaimer]