Web Audio API - Find combined amplitude gain of biquad filters

filter-gain.js

/**
 * Calculates maximum gain for a set of biquad filters. The function will calculate 
 * frequency response in steps specified by precisionHz
 *
 * @param {BiquadFilterNode[]} filters The array of biquad filters,
 * @param {number} precisionHz A resolution in hertz of the calculation - smaller value means higher precision. Default value: 20.
 * @return {number} Gain of the filters in dB.
 */
function maxGain(filters, precisionHz) {
  if (!filters || filters.length === 0)
    return 0;
  
  precisionHz = Math.max(1, precisionHz || 20);
  const maxFrequency = filters[0].context.sampleRate;
  const steps = Math.ceil(maxFrequency / precisionHz);
  // Generate input array for getFrequencyResponse method
  const frequencies = new Float32Array(steps);
  for (let i = 0; i < steps; i++) {
      frequencies[i] = (i + 1) * precisionHz;
  }
  // Here we will store combined amplitude response
  const totalAmplitudeResp = new Float32Array(steps);
  for (let i = 0; i < steps; i++) {
      totalAmplitudeResp[i] = 1;
  }
  // Temporary container for every filter response
  const amplitudeResp = new Float32Array(steps), phaseResp = new Float32Array(steps);
  for (let i = filters.length - 1; i >= 0; i--) {
      const filter = filters[i];
      // Get filter response and convolve it with existing response
      filter.getFrequencyResponse(frequencies, amplitudeResp, phaseResp);
      for (let j = 0; j < steps; j++) {
          totalAmplitudeResp[j] *= amplitudeResp[j];
      }
  }
  // Find max gain
  let maxGain = -10000000;
  for (let i = 0; i < steps; i++) {
      const gain = totalAmplitudeResp[i];
      if (gain > maxGain)
          maxGain = gain;
  }
  // Convert gain to dB
  filterGain = maxGain > 1.0 ? 20 * Math.log10(maxGain) : 0;
  return filterGain;
}