Add volume_max_db setting which works on the hw mixer if it exists or the sw attenuator otherwise.

common.c

@@ -559,7 +559,7 @@ double vol2attn(double vol, long max_db, long min_db) {
   double vol_setting = 0;
 
   if ((vol <= 0.0) && (vol >= -30.0)) {
-    long range_db = max_db - min_db; // this will be a positive nunmber
+    long range_db = max_db - min_db; // this will be a positive number
     // debug(1,"Volume min %ddB, max %ddB, range %ddB.",min_db,max_db,range_db);
     // double first_slope = -3000.0; // this is the slope of the attenuation at the high end -- 30dB
     // for the full rotation.

common.h

@@ -87,6 +87,8 @@ typedef struct {
   int udp_port_base;
   int udp_port_range;
   int ignore_volume_control;
+  int volume_max_db_set;  // set to 1 if a maximum volume db has been set
+  int volume_max_db;
   int no_sync;            // disable synchronisation, even if it's available
   int no_mmap;            // disable use of mmap-based output, even if it's available
   double resyncthreshold; // if it get's out of whack my more than this number of seconds, resync.

player.c

@@ -2259,16 +2259,6 @@ void player_volume(double airplay_volume) {
   int32_t hw_min_db, hw_max_db, hw_range_db, range_to_use, min_db,
       max_db; // hw_range_db is a flag; if 0 means no mixer
 
-  int32_t sw_min_db = -9630;
-  int32_t sw_max_db = 0;
-  int32_t sw_range_db = sw_max_db - sw_min_db;
-  int32_t desired_range_db; // this is used as a flag; if 0 means no desired range
-
-  if (config.volume_range_db)
-    desired_range_db = (int32_t)trunc(config.volume_range_db * 100);
-  else
-    desired_range_db = 0;
-
   if (config.output->parameters) {
     // have a hardware mixer
     config.output->parameters(&audio_information);
@@ -2279,7 +2269,34 @@ void player_volume(double airplay_volume) {
     // don't have a hardware mixer
     hw_max_db = hw_min_db = hw_range_db = 0;
   }
+  
+  int32_t sw_min_db = -9630;
+  int32_t sw_max_db = 0;
+  int32_t sw_range_db = sw_max_db - sw_min_db;
+  int32_t desired_range_db = 0; // this is used as a flag; if 0 means no desired range
 
+  if (config.volume_range_db)
+    desired_range_db = (int32_t)trunc(config.volume_range_db * 100);
+
+   if (config.volume_max_db_set) {
+    if (hw_range_db) {
+      if (((config.volume_max_db*100)<hw_max_db) && ((config.volume_max_db*100)>hw_min_db)) {
+        hw_max_db = (int)config.volume_max_db*100;
+        hw_range_db = hw_max_db-hw_min_db;
+      } else {
+        inform("The volume_max_db setting is out of range of the hardware mixers's limits of %d dB to %d dB. It will be ignored.", (int)(hw_max_db/100), (int)(hw_min_db/100));
+      }
+    } else {
+      if (((config.volume_max_db*100)<sw_max_db) && ((config.volume_max_db*100)>sw_min_db)) {
+        sw_max_db = (int)config.volume_max_db*100;
+        sw_range_db = sw_max_db-sw_min_db;
+      } else {
+        inform("The volume_max_db setting is out of range of the software attenuation's limits of 0 dB to -96.3 dB. It will be ignored.");
+      }
+    }      
+   }
+
+  
   if (desired_range_db) {
     // debug(1,"An attenuation range of %d is requested.",desired_range_db);
     // we have a desired volume range.
@@ -2322,6 +2339,16 @@ void player_volume(double airplay_volume) {
     }
   }
 
+/*
+  if (config.volume_max_db_set) {
+    if ((config.volume_max_db*100<=max_db) && (config.volume_max_db*100>=min_db)) {
+      debug(1,"Reducing the maximum volume from %d to %d.",max_db/100,config.volume_max_db);
+      max_db = (int)(config.volume_max_db*100);
+    } else {
+      inform("The value of volume_max_db is invalid. It must be in the range %d to %d.",max_db,min_db);
+    }  
+  }
+*/
   double hardware_attenuation, software_attenuation;
   double scaled_attenuation = hw_min_db + sw_min_db;
 

shairport.c

@@ -474,6 +474,13 @@ int parse_options(int argc, char **argv) {
         else
           die("Invalid ignore_volume_control option choice \"%s\". It should be \"yes\" or \"no\"");
       }
+      
+     /* Get the optional volume_max_db setting. */
+      if (config_lookup_float(config.cfg, "general.volume_max_db", &dvalue)) {
+        debug(1,"Max volume setting of %f dB",dvalue);
+        config.volume_max_db = dvalue;
+        config.volume_max_db_set = 1;
+      }
 
       /* Get the playback_mode setting */
       if (config_lookup_string(config.cfg, "general.playback_mode", &str)) {
@@ -491,9 +498,6 @@ int parse_options(int argc, char **argv) {
           die("Invalid playback_mode choice \"%s\". It should be \"stereo\" (default), \"mono\", "
               "\"reverse stereo\", \"both left\", \"both right\"");
       }
-      
-      
-      
 
       /* Get the interface to listen on, if specified Default is all interfaces */
       /* we keep the interface name and the index */