When the fader is moved, interpolate its volume over the next frame.

Faders are among the things one should definitely be allowed to move
around during an actual mix without hearing clicking; the gain and threshold
is maybe somewhat less so, so I won't give it the same treatment, at least not
right now.

diff --git a/audio_mixer.cpp b/audio_mixer.cpp
index 7810b43ab8fb991d79387ec135ba4c701254dfe6..18a669f0eb8bcfe399b09cbf305d8718617b6203 100644 (file)
--- a/audio_mixer.cpp
+++ b/audio_mixer.cpp
@@ -462,19 +462,9 @@ vector<float> AudioMixer::get_output(double pts, unsigned num_samples, Resamplin
                        }
                }
 
-               float volume = from_db(fader_volume_db[bus_index]);
-               if (bus_index == 0) {
-                       for (unsigned i = 0; i < num_samples * 2; ++i) {
-                               samples_out[i] = samples_bus[i] * volume;
-                       }
-               } else {
-                       for (unsigned i = 0; i < num_samples * 2; ++i) {
-                               samples_out[i] += samples_bus[i] * volume;
-                       }
-               }
-
+               add_bus_to_master(bus_index, samples_bus, &samples_out);
                deinterleave_samples(samples_bus, &left, &right);
-               measure_bus_levels(bus_index, left, right, volume);
+               measure_bus_levels(bus_index, left, right);
        }
 
        {
@@ -541,9 +531,56 @@ vector<float> AudioMixer::get_output(double pts, unsigned num_samples, Resamplin
        return samples_out;
 }
 
-void AudioMixer::measure_bus_levels(unsigned bus_index, const vector<float> &left, const vector<float> &right, float volume)
+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

diff --git a/audio_mixer.h b/audio_mixer.h
index 5d65582c939fa191bcf8efad870d6e1c65b65c25..29016eb9ea7e07a68257bb8c02b6617edc4c4b6d 100644 (file)
--- a/audio_mixer.h
+++ b/audio_mixer.h
@@ -238,7 +238,8 @@ private:
        void reset_alsa_mutex_held(DeviceSpec device_spec);
        std::map<DeviceSpec, DeviceInfo> get_devices_mutex_held() const;
        void update_meters(const std::vector<float> &samples);
-       void measure_bus_levels(unsigned bus_index, const std::vector<float> &left, const std::vector<float> &right, float volume);
+       void add_bus_to_master(unsigned bus_index, const std::vector<float> &samples_bus, std::vector<float> *samples_out);
+       void measure_bus_levels(unsigned bus_index, const std::vector<float> &left, const std::vector<float> &right);
        void send_audio_level_callback();
 
        unsigned num_cards;
@@ -286,6 +287,7 @@ private:
 
        InputMapping input_mapping;  // Under audio_mutex.
        std::atomic<float> fader_volume_db[MAX_BUSES] {{ 0.0f }};
+       float last_fader_volume_db[MAX_BUSES] { 0.0f };  // Under audio_mutex.
 
        audio_level_callback_t audio_level_callback = nullptr;
        mutable std::mutex audio_measure_mutex;