+void AudioMixer::add_bus_to_master(unsigned bus_index, const vector<float> &samples_bus, vector<float> *samples_out)
+{
+ assert(samples_bus.size() == samples_out->size());
+ assert(samples_bus.size() % 2 == 0);
+ unsigned num_samples = samples_bus.size() / 2;
+ if (fabs(fader_volume_db[bus_index] - last_fader_volume_db[bus_index]) > 1e-3) {
+ // The volume has changed; do a fade over the course of this frame.
+ // (We might have some numerical issues here, but it seems to sound OK.)
+ // For the purpose of fading here, the silence floor is set to -90 dB
+ // (the fader only goes to -84).
+ float old_volume = from_db(max<float>(last_fader_volume_db[bus_index], -90.0f));
+ float volume = from_db(max<float>(fader_volume_db[bus_index], -90.0f));
+
+ float volume_inc = pow(volume / old_volume, 1.0 / num_samples);
+ volume = old_volume;
+ if (bus_index == 0) {
+ for (unsigned i = 0; i < num_samples; ++i) {
+ (*samples_out)[i * 2 + 0] = samples_bus[i * 2 + 0] * volume;
+ (*samples_out)[i * 2 + 1] = samples_bus[i * 2 + 1] * volume;
+ volume *= volume_inc;
+ }
+ } else {
+ for (unsigned i = 0; i < num_samples; ++i) {
+ (*samples_out)[i * 2 + 0] += samples_bus[i * 2 + 0] * volume;
+ (*samples_out)[i * 2 + 1] += samples_bus[i * 2 + 1] * volume;
+ volume *= volume_inc;
+ }
+ }
+ } else {
+ float volume = from_db(fader_volume_db[bus_index]);
+ if (bus_index == 0) {
+ for (unsigned i = 0; i < num_samples; ++i) {
+ (*samples_out)[i * 2 + 0] = samples_bus[i * 2 + 0] * volume;
+ (*samples_out)[i * 2 + 1] = samples_bus[i * 2 + 1] * volume;
+ }
+ } else {
+ for (unsigned i = 0; i < num_samples; ++i) {
+ (*samples_out)[i * 2 + 0] += samples_bus[i * 2 + 0] * volume;
+ (*samples_out)[i * 2 + 1] += samples_bus[i * 2 + 1] * volume;
+ }
+ }
+ }
+
+ last_fader_volume_db[bus_index] = fader_volume_db[bus_index];
+}
+
+void AudioMixer::measure_bus_levels(unsigned bus_index, const vector<float> &left, const vector<float> &right)
+{
+ assert(left.size() == right.size());
+ const float volume = from_db(fader_volume_db[bus_index]);
+ const float peak_levels[2] = {
+ find_peak(left.data(), left.size()) * volume,
+ find_peak(right.data(), right.size()) * volume
+ };
+ for (unsigned channel = 0; channel < 2; ++channel) {
+ // Compute the current value, including hold and falloff.
+ // The constants are borrowed from zita-mu1 by Fons Adriaensen.
+ static constexpr float hold_sec = 0.5f;
+ static constexpr float falloff_db_sec = 15.0f; // dB/sec falloff after hold.
+ float current_peak;
+ PeakHistory &history = peak_history[bus_index][channel];
+ history.historic_peak = max(history.historic_peak, peak_levels[channel]);
+ if (history.age_seconds < hold_sec) {
+ current_peak = history.last_peak;
+ } else {
+ current_peak = history.last_peak * from_db(-falloff_db_sec * (history.age_seconds - hold_sec));
+ }
+
+ // See if we have a new peak to replace the old (possibly falling) one.
+ if (peak_levels[channel] > current_peak) {
+ history.last_peak = peak_levels[channel];
+ history.age_seconds = 0.0f; // Not 100% correct, but more than good enough given our frame sizes.
+ current_peak = peak_levels[channel];
+ } else {
+ history.age_seconds += float(left.size()) / OUTPUT_FREQUENCY;
+ }
+ history.current_level = peak_levels[channel];
+ history.current_peak = current_peak;
+ }
+}
+