private static bool initialized = false;

        static float param_cutoff, param_resonance;
        static float[] filtCoefTab = new float[5];
        static float lx1, lx2, ly1, ly2; // Left sample history

        private static void InitLPF()
        {
            param_cutoff = 22050;
            param_resonance = 0;
            InitFiltah();
            lx1 = lx2 = ly1 = ly2 = 0.0f;
        }

        private static void InitFiltah()
        {
            float alpha, omega, sn, cs;
            float a0, a1, a2, b0, b1, b2;

            // These limits the cutoff frequency and resonance to
            // reasoneable values.
            if (param_cutoff < 20.0f) { param_cutoff = 20.0f; };
            if (param_cutoff > 22000.0f) { param_cutoff = 22000.0f; };
            if (param_resonance < 1.0f) { param_resonance = 1.0f; };
            if (param_resonance > 127.0f) { param_resonance = 127.0f; };

            omega = (float)(2.0f * Math.PI * param_cutoff / 44100);
            sn = (float)Math.Sin(omega);
            cs = (float)Math.Cos(omega);
            alpha = sn / param_resonance;
            b0 = (1.0f - cs) / 2.0f;
            b1 = 1.0f - cs;
            b2 = (1.0f - cs) / 2.0f;
            a0 = 1.0f + alpha;
            a1 = -2.0f * cs;
            a2 = 1.0f - alpha;
            filtCoefTab[0] = b0 / a0;
            filtCoefTab[1] = b1 / a0;
            filtCoefTab[2] = b2 / a0;
            filtCoefTab[3] = -a1 / a0;
            filtCoefTab[4] = -a2 / a0;
        }

        public static void EffectLpf(Int32[] input)
        {
            if (!initialized) InitLPF();

            int inM, outM, temp_y;
            int i;

            for (i = 0; i < input.Length; i++)
            {

                inM = input[i];

                outM = inM;

                temp_y = (int)(filtCoefTab[0] * outM +
                                filtCoefTab[1] * lx1 +
                                filtCoefTab[2] * lx2 +
                                filtCoefTab[3] * ly1 +
                                filtCoefTab[4] * ly2);
                ly2 = ly1; ly1 = temp_y; lx2 = lx1; lx1 = outM; outM = temp_y;

                i++;
                input[i] = outM;
            }
        }