Index: head/share/man/man4/pcm.4
===================================================================
--- head/share/man/man4/pcm.4
+++ head/share/man/man4/pcm.4
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 22, 2012
+.Dd May 5, 2020
 .Dt SOUND 4
 .Os
 .Sh NAME
@@ -743,8 +743,8 @@
 .Xr mixer 8 ,
 .Xr sysctl 8
 .Rs
-.%T "Cookbook formulae for audio EQ biquad filter coefficients, by Robert Bristow-Johnson"
-.%U "http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt"
+.%T "Cookbook formulae for audio EQ biquad filter coefficients (Audio-EQ-Cookbook.txt), by Robert Bristow-Johnson"
+.%U "https://www.musicdsp.org/en/latest/Filters/197-rbj-audio-eq-cookbook.html"
 .Re
 .Rs
 .%T "Julius O'Smith's Digital Audio Resampling"
@@ -752,7 +752,7 @@
 .Re
 .Rs
 .%T "Polynomial Interpolators for High-Quality Resampling of Oversampled Audio, by Olli Niemitalo"
-.%U "http://www.student.oulu.fi/~oniemita/dsp/deip.pdf"
+.%U "http://yehar.com/blog/wp-content/uploads/2009/08/deip.pdf"
 .Re
 .Rs
 .%T "The OSS API"