code: void lpc_to_curve(float[] curve, float[] lpc, float amp){
  
      for(int i=0; i<ln*2; i++)
        curve[i]=0.0f;
  
      if(amp==0)
        return;
  
      for(int i=0; i<m; i++){
        curve[i*2+1]=lpc[i]/(4*amp);
        curve[i*2+2]=-lpc[i]/(4*amp);
      }
  
      fft.backward(curve);
  
      {
        int l2=ln*2;
        float unit=(float)(1./amp);
        curve[0]=(float)(1./(curve[0]*2+unit));
        for(int i=1; i<ln; i++){
          float real=(curve[i]+curve[l2-i]);
          float imag=(curve[i]-curve[l2-i]);
  
          float a=real+unit;
          curve[i]=(float)(1.0/FAST_HYPOT(a, imag));
        }
      }
    }
docs: interpolates the log curve from the linear curve.