      let biquad = context.createBiquadFilter();

        // Create the equivalent IIR Filter node.
        let nyquist = sampleRate / 2;
        let coef = createFilter(
            biquad.type, biquad.frequency.value / nyquist, biquad.Q.value,
            biquad.gain.value);
        let fb = [1, coef.a1, coef.a2];
        let ff = [coef.b0, coef.b1, coef.b2];

        let iir = context.createIIRFilter(ff, fb);
        // Gain node to compute the difference between the IIR and biquad
        // filter.
   