playing with using just a linear mixer

diff --git a/audio_alsa.c b/audio_alsa.c
index d4e5497375bd6a83ed750a43a4c29c0dc1cf300d..309a8314520bc0f1e4775eea1ba520806a7ade40 100644 (file)
--- a/audio_alsa.c
+++ b/audio_alsa.c
@@ -29,6 +29,7 @@
 #include <stdio.h>
 #include <unistd.h>
 #include <memory.h>
+#include <math.h>
 #include <pthread.h>
 #include <alsa/asoundlib.h>
 #include "common.h"
@@ -43,9 +44,9 @@ static void stop(void);
 static void flush(void);
 static uint32_t delay(void);
 static void volume(double vol);
+static void linear_volume(double vol);
 static void parameters(audio_parameters *info);
 static int has_mute = 0;
-static int has_db_vol = 0;
 static double set_volume;
 
 audio_output audio_alsa = {
@@ -209,12 +210,37 @@ static int init(int argc, char **argv) {
   alsa_mix_elem = snd_mixer_find_selem(alsa_mix_handle, alsa_mix_sid);
   if (!alsa_mix_elem)
     die("Failed to find mixer element");
+  // Check that the output device has two playback channels
+  snd_mixer_selem_channel_id_t chn;
+  
+  
+  if (snd_mixer_selem_has_playback_volume(alsa_mix_elem) ||
+           snd_mixer_selem_has_playback_switch(alsa_mix_elem)) {
+               if (snd_mixer_selem_is_playback_mono(alsa_mix_elem)) {
+                       debug(1,"Mono Capable Output Device Only");
+               } else {
+                       for (chn = 0; chn <= SND_MIXER_SCHN_LAST; chn++){
+                               if (snd_mixer_selem_has_playback_channel(alsa_mix_elem, chn)) {
+                                 debug(1,"Playback channel \"%s\" discovered", snd_mixer_selem_channel_name(chn));
+                                 // see if it's got a dB range
+                                 int64_t cmin,cmax;
+                                 if (snd_mixer_selem_get_playback_dB_range(alsa_mix_elem,&cmin,&cmax)==0)
+                                   debug(1,"Range in dB is from %ld to %ld",cmin,cmax);
+                                 else
+                                   debug(1,"Can't get dB volume range");
+                               }
+                       }
+               }
+       }
+
+  
+  
   if (snd_mixer_selem_get_playback_volume_range(alsa_mix_elem, &alsa_mix_minv, &alsa_mix_maxv) < 0)
     debug(1, "Can't read mixer's [linear] min and max volumes.");
   else {
-    if ((snd_mixer_selem_ask_playback_vol_dB(alsa_mix_elem, alsa_mix_minv, &alsa_mix_mindb) == 0) &&
-        (snd_mixer_selem_ask_playback_vol_dB(alsa_mix_elem, alsa_mix_maxv, &alsa_mix_maxdb) == 0)) {
-      has_db_vol = 1;
+    if (snd_mixer_selem_get_playback_dB_range (alsa_mix_elem, &alsa_mix_mindb, &alsa_mix_maxdb) == 0) {
+//    if ((snd_mixer_selem_ask_playback_vol_dB(alsa_mix_elem, alsa_mix_minv, &alsa_mix_mindb) == 0) &&
+//        (snd_mixer_selem_ask_playback_vol_dB(alsa_mix_elem, alsa_mix_maxv, &alsa_mix_maxdb) == 0)) {
       audio_alsa.volume = &volume; // insert the volume function now we know it can do dB stuff
       audio_alsa.parameters = &parameters; // likewise the parameters stuff
       if (alsa_mix_mindb == -9999999) {
@@ -226,8 +252,17 @@ static int init(int argc, char **argv) {
       debug(1, "Hardware mixer has dB volume from %f to %f.", (1.0 * alsa_mix_mindb) / 100.0,
             (1.0 * alsa_mix_maxdb) / 100.0);
     } else {
+      // use the linear scale and do the db conversion ourselves
       inform("note: the hardware mixer specified -- \"%s\" -- does not have dB volume, so it can not be used for volume control.",alsa_mix_ctrl);
-    }
+      debug(1, "Min and max volumes are %d and %d.",alsa_mix_minv,alsa_mix_maxv);
+      alsa_mix_maxdb = 0;
+      if ((alsa_mix_maxv!=0) && (alsa_mix_minv!=0))
+        alsa_mix_mindb = -20*100*(log10(alsa_mix_maxv*1.0)-log10(alsa_mix_minv*1.0));
+      else if (alsa_mix_maxv!=0)
+        alsa_mix_mindb = -20*100*log10(alsa_mix_maxv*1.0);
+      audio_alsa.volume = &linear_volume; // insert the linear volume function
+      debug(1,"Max and min dB calculated are %d and %d.",alsa_mix_maxdb,alsa_mix_mindb);
+     }
   }
   if (snd_mixer_selem_has_playback_switch(alsa_mix_elem)) {
     has_mute = 1;
@@ -320,7 +355,7 @@ static void play(short buf[], int samples) {
   if (alsa_handle == NULL) {
     ret = open_alsa_device();
     if ((ret == 0) && (audio_alsa.volume))
-      volume(set_volume);
+      audio_alsa.volume(set_volume);
   }
   if (ret == 0) {
     pthread_mutex_lock(&alsa_mutex);
@@ -390,6 +425,7 @@ static void parameters(audio_parameters *info) {
 }
 
 static void volume(double vol) {
+  debug(1,"Setting volume in dB.");
   set_volume = vol;
   double vol_setting = vol2attn(vol, alsa_mix_maxdb, alsa_mix_mindb);
   // debug(1,"Setting volume db to %f, for volume input of %f.",vol_setting/100,vol);
@@ -398,3 +434,18 @@ static void volume(double vol) {
   if (has_mute)
     snd_mixer_selem_set_playback_switch_all(alsa_mix_elem, (vol != -144.0));
 }
+
+static void linear_volume(double vol) {
+  debug(1,"Setting linear volume for %f.",vol);
+  set_volume = vol;
+  double vol_setting = vol2attn(vol, 0, alsa_mix_mindb)/2000;
+  debug(1,"Adjusted volume is %f.",vol_setting);
+  double linear_volume = pow(10, vol_setting);
+  debug(1,"Linear volume is %f.",linear_volume);
+  long int_vol = alsa_mix_minv + (alsa_mix_maxv - alsa_mix_minv) * linear_volume;
+  debug(1,"Setting volume to %ld, for volume input of %f.",int_vol,vol);
+  if (snd_mixer_selem_set_playback_volume_all(alsa_mix_elem, int_vol) != 0)
+    die("Failed to set playback volume");
+  if (has_mute)
+    snd_mixer_selem_set_playback_switch_all(alsa_mix_elem, (vol != -144.0));
+}

diff --git a/player.c b/player.c
index 80fcae2269eaeef307b42389944f25b0ec7e413f..b7224e5eeeebfc3a8a9e3ecc4e8ae67fe0f01320 100644 (file)
--- a/player.c
+++ b/player.c
@@ -1196,32 +1196,35 @@ void player_volume(double f) {
   // The volume ranges -144.0 (mute) or -30 -- 0. See
   // http://git.zx2c4.com/Airtunes2/about/#setting-volume
   // By examination, the -30 -- 0 range is linear on the slider; i.e. the slider is calibrated in 30
-  // equal increments
-  // So, we will pass this on without any weighting if we have a hardware mixer, as we expect the
-  // mixer to be calibrated in dB.
-
-  // Here, we ask for an attenuation we will apply in software. The dB range of a value from 1 to
-  // 65536 is about 48.1 dB (log10 of 65536 is 4.8164).
-  // Thus, we ask our vol2attn function for an appropriate dB between -48.1 and 0 dB and translate
+  // equal increments. Since the human ear's response is roughly logarithmic, we imagine these to
+  // be power dB, i.e. from -30dB to 0dB.
+  
+  // So, if we have a hardware mixer, we will pass this on to its dB volume settings.
+  
+  // Without a hardware mixer, we have to do attenuation in software, so
+  // here, we ask for an attenuation we will apply to the signal amplitude in software.
+  // The dB range of a value from 1 to 65536 is about 96.3 dB (log10 of 65536 is 4.8164).
+  // Since the levels correspond with amplitude, they correspond to voltage, hence voltage dB,
+  // or 20 times the log of the ratio. Then multiplied by 100 for convenience.
+  // Thus, we ask our vol2attn function for an appropriate dB between -96.3 and 0 dB and translate
   // it back to a number.
 
-  double scaled_volume = vol2attn(f, 0, -4810);
-  double linear_volume = pow(10, scaled_volume / 1000);
+  double scaled_volume = vol2attn(f, 0, -9630);
+  double linear_volume = pow(10, scaled_volume / 20*100);
 
   if (f == -144.0)
     linear_volume = 0.0;
 
   if (config.output->volume) {
     config.output->volume(f); // volume will be sent as metadata by the config.output device
-    linear_volume =
-        1.0; // no attenuation needed -- this value is used as a flag to avoid calculations
+    linear_volume = 1.0; // no attenuation needed -- this value is used as a flag to avoid calculations
   }
 
   if (config.output->parameters)
     config.output->parameters(&audio_information);
   else {
     audio_information.airplay_volume = f;
-    audio_information.minimum_volume_dB = -4810;
+    audio_information.minimum_volume_dB = -9630;
     audio_information.maximum_volume_dB = 0;
     audio_information.current_volume_dB = scaled_volume;
     audio_information.has_true_mute = 0;
@@ -1233,10 +1236,10 @@ void player_volume(double f) {
   fix_volume = 65536.0 * software_mixer_volume;
   pthread_mutex_unlock(&vol_mutex);
 #ifdef CONFIG_METADATA
-  char *dv = malloc(64); // will be freed in the metadata thread
+  char *dv = malloc(128); // will be freed in the metadata thread
   if (dv) {
-    memset(dv, 0, 64);
-    snprintf(dv, 63, "%.2f,%.2f,%.2f,%.2f", audio_information.airplay_volume,
+    memset(dv, 0, 128);
+    snprintf(dv, 127, "%.2f,%.2f,%.2f,%.2f", audio_information.airplay_volume,
              audio_information.current_volume_dB / 100.0,
              audio_information.minimum_volume_dB / 100.0,
              audio_information.maximum_volume_dB / 100.0);