Hi,

>I am new to Csound and I have tried to make a FM algorithm with feedback
>loop.

I don't know about Visual Orchestra but the trick is to init the variable to
0 before the loop back, something like:

      instr 1

iamp  =     p4
ifqc  =     cpspch(p5)
iatt  =     p6
adec  =     p7
islev =     p8
irel  =     p9

a1    init  0

aenv  adsr  iatt, idec, islev, irel

a1    oscil aenv, ifqc*(1+a1), 1

      outs  a1, a1

      endin

The pitch tends to drift somewhat though I think.

Bye,
Hans Mikelson