subroutine interv1(j,fre,nf,df,spe,nf1,smo,n_win,lw)
c
c linear interpolation of 'spe' at frequency = 'fre(j)'
c a.tento 05/03 v.1.0. 
c
        implicit none
        real fre, spe, smo, df
        integer nf, nf1, lw, n_win
        dimension fre(nf), spe(nf1), smo(nf,n_win)
c
        integer j, i1, i2
        real bb
c
        i1 = int(fre(j)/df) + 1
        i2 = i1 + 1
c   df <= fre(j) <= fny  by deffre
        if (i2  .ge.  nf1) i2 = nf1
        bb = ( spe(i2)  -  spe(i1) ) / df
        smo(j,lw) = spe(i1) + bb * ( fre(j) - df*float(i1-1) )
c
        return
c
        end