Prefabricated low-, high-, and band-pass filters</A>
</H2>
<P>
Patches H01.low-pass.pd, H02.high-pass.pd, and H03.band-pass.pd (Figure <AHREF="#fig08.28">8.28</A>) show Pd's
built-in filters, which implement filter designs described in Sections
<AHREF="node140.html#sect08.low-pass">8.3.1</A>, <AHREF="node141.html#sect08.highpass">8.3.2</A> and <AHREF="node143.html#sect8.twopolebandpass">8.3.4</A>.
Two of the patches also use a noise generator we have not introduced before.
We will need four new Pd objects:
<P>
<BR><!-- MATH
$\fbox{\texttt{lop\~}}$
-->
<IMG
WIDTH="47" HEIGHT="39" ALIGN="MIDDLE" BORDER="0"
SRC="img1014.png"
ALT="\fbox{\texttt{lop\~}}">:
<ANAME="10842"></A>one-pole low-pass filter. The left inlet takes a signal to be filtered, and
the right inlet takes control messages to set the
cutoff frequency of the filter. The filter is normalized so that the
gain is one at frequency 0.
<P>
<BR><!-- MATH
$\fbox{ \texttt{hip\~}}$
-->
<IMG
WIDTH="53" HEIGHT="39" ALIGN="MIDDLE" BORDER="0"
SRC="img1016.png"
ALT="\fbox{ \texttt{hip\~}}">:
<ANAME="10843"></A>one-pole, one-zero high-pass filter, with the same inputs and outputs as
<TT>lop~</TT>, normalized to have a gain of one at the Nyquist frequency.
<P>
<BR><!-- MATH
$\fbox{ \texttt{bp\~}}$
-->
<IMG
WIDTH="44" HEIGHT="39" ALIGN="MIDDLE" BORDER="0"
SRC="img1017.png"
ALT="\fbox{ \texttt{bp\~}}">:
<ANAME="10844"></A>resonant filter. The middle inlet takes control messages to set the center
frequency, and the right inlet to set ``q".
<P>
<BR><!-- MATH
$\fbox{ \texttt{noise\~}}$
-->
<IMG
WIDTH="69" HEIGHT="39" ALIGN="MIDDLE" BORDER="0"
SRC="img1019.png"
ALT="\fbox{ \texttt{noise\~}}">:
<ANAME="10845"></A>white noise generator. Each sample is an independent
pseudo-random number, uniformly distributed from -1 to 1.
