THEORY: Fricatives

As I posted earlier, can anybody help me?

I have noticed a difference in what is usually called fricatives when
making experiments for my degree exam.  In an spectral view (frecuency
against time), some characteristics can be found, usually realted to the
articulation of the sounds.

There are two groups of fricatives (and affricates) which are easily
told appart from their spectral views.  The first group includes /s/,
/f/, /tS/, /j\/ (voiced palatal fricative) the other group includes /B/,
/G/, /h/ and my variant of /D/ which is more alveolar than dental (IPA?,
SAMPA?).

Does this differenciation have a name?
Does it explain the difference between Colombian fricative <d> which is
alveolar and the voiced allophone of /s/.

Thank you.

--
Carlos Eugenio Thompson Pinz=F3n
  ITEC-Telecom, Colombia

  cthompso@alpha.telecom-co.net
  http://alpha.telecom-co.net/~cthompso/

Di mi beh em je lok mi ju je kom lon vu am je