lincontrol[variable_, default_, min_, max_] :=
 {{{variable, default}, min, max},
  Panel[ToString[variable ] <> "=" Dynamic[variable]]}

Manipulate[Module[{spectrum},
  spectrum = (x=y^2 +a*b;
  Plot[spectrum, {x, -10, 10}]],
 Flatten[{lincontrol[#, 1, 0, 10] &/@ {y,a,b}}, 2]]