I am trying to build freeswitch on Ubuntu and getting numerous libraries absent. One of them is speex. configure says it is absent while dpkg says it is here:

checking for speex >= 1.2rc1 speexdsp >= 1.2rc1... Package speex was not found in the pkg-config search path. Perhaps you should add the directory containing `speex.pc' to the PKG_CONFIG_PATH environment variable No package 'speex' found Package speexdsp was not found in the pkg-config search path. Perhaps you should add the directory containing `speexdsp.pc' to the PKG_CONFIG_PATH environment variable No package 'speexdsp' found

configure: error: Library requirements (speex >= 1.2rc1 speexdsp >= 1.2rc1) not met; consider adjusting the PKG_CONFIG_PATH environment variable if your libraries are in a nonstandard prefix so pkg-config can find them.

dims@nebula2:~/src/freeswitch$ dpkg -l *speex*

Desired=Unknown/Install/Remove/Purge/Hold

| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend

|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)

||/ Name                             Version                          Description

+++-================================-================================-================================================================================

ii  libspeex1                        1.2~rc1-3ubuntu2                 The Speex codec runtime library

ii  libspeexdsp1                     1.2~rc1-3ubuntu2                 The Speex extended runtime library

ii  speex                            1.2~rc1-3ubuntu2                 The Speex codec command line tools

why? and how to fix?