Add new "dasl_tapered" volume control profile

common.c

@@ -37,6 +37,7 @@
 #include <fcntl.h>
 #include <inttypes.h> // PRIdPTR
 #include <libgen.h>
+#include <math.h>
 #include <memory.h>
 #include <poll.h>
 #include <popt.h>
@@ -1205,6 +1206,32 @@ double flat_vol2attn(double vol, long max_db, long min_db) {
  }
  return vol_setting;
 }
+
+double dasl_tapered_vol2attn(double vol, long max_db, long min_db) {
+ double vol_setting = min_db; // if all else fails, set this, for safety
+
+ if ((vol <= 0.0) && (vol >= -30.0)) {
+ double vol_pct = 1 - (vol / -30.0); // This will be in the range [0, 1]
+ if (vol_pct <= 0) {
+ return min_db;
+ }
+
+ vol_setting = max_db + 1000 * log10(vol_pct) / log10(2); // This will be in the range [-inf, max_db]
+ if (vol_setting < min_db) {
+ return min_db;
+ }
+ if (vol_setting > max_db) {
+ return max_db;
+ }
+ return vol_setting;
+ } else if (vol != -144.0) {
+ debug(1,
+ "dasl_tapered volume request value %f is out of range: should be from 0.0 to -30.0 or -144.0.",
+ vol);
+ }
+ return vol_setting;
+}
+
 // Given a volume (0 to -30) and high and low attenuations available in the mixer in dB, return an
 // attenuation depending on the volume and the function's transfer function
 // See http://tangentsoft.net/audio/atten.html for data on good attenuators.

common.h

@@ -73,6 +73,7 @@ typedef enum {
 typedef enum {
  VCP_standard = 0,
  VCP_flat,
+ VCP_dasl_tapered,
 } volume_control_profile_type;
 
 typedef enum {
@@ -387,9 +388,16 @@ char *base64_enc(uint8_t *input, int length);
 uint8_t *rsa_apply(uint8_t *input, int inlen, int *outlen, int mode);
 
 // given a volume (0 to -30) and high and low attenuations in dB*100 (e.g. 0 to -6000 for 0 to -60
-// dB), return an attenuation depending on a linear interpolation along along the range
+// dB), return an attenuation depending on a linear interpolation along the range
 double flat_vol2attn(double vol, long max_db, long min_db);
 
+// given a volume (0 to -30) and high and low attenuations in dB*100 (e.g. 0 to -6000 for 0 to -60
+// dB), return an attenuation depending on a logarithmic interpolation along the range.
+// The intention behind this attenuation function is that a given percentage change in volume
+// should result in the same percentage change in perceived loudness. For instance, a doubling
+// (100% increase) of volume level should result in a doubling of perceived loudness.
+double dasl_tapered_vol2attn(double vol, long max_db, long min_db);
+
 // given a volume (0 to -30) and high and low attenuations in dB*100 (e.g. 0 to -6000 for 0 to -60
 // dB), return an attenuation depending on the transfer function
 double vol2attn(double vol, long max_db, long min_db);

dbus-service.c

@@ -765,6 +765,8 @@ gboolean notify_volume_control_profile_callback(ShairportSync *skeleton,
  config.volume_control_profile = VCP_standard;
  else if (strcasecmp(th, "flat") == 0)
  config.volume_control_profile = VCP_flat;
+ else if (strcasecmp(th, "dasl_tapered") == 0)
+ config.volume_control_profile = VCP_dasl_tapered;
  else {
  warn("Unrecognised Volume Control Profile: \"%s\".", th);
  switch (config.volume_control_profile) {
@@ -774,6 +776,9 @@ gboolean notify_volume_control_profile_callback(ShairportSync *skeleton,
  case VCP_flat:
  shairport_sync_set_volume_control_profile(skeleton, "flat");
  break;
+ case VCP_dasl_tapered:
+ shairport_sync_set_volume_control_profile(skeleton, "dasl_tapered");
+ break;
  default:
  debug(1, "This should never happen!");
  shairport_sync_set_volume_control_profile(skeleton, "standard");
@@ -1065,6 +1070,8 @@ static void on_dbus_name_acquired(GDBusConnection *connection, const gchar *name
 
  if (config.volume_control_profile == VCP_standard)
  shairport_sync_set_volume_control_profile(SHAIRPORT_SYNC(shairportSyncSkeleton), "standard");
+ else if (config.volume_control_profile == VCP_dasl_tapered)
+ shairport_sync_set_volume_control_profile(SHAIRPORT_SYNC(shairportSyncSkeleton), "dasl_tapered");
  else
  shairport_sync_set_volume_control_profile(SHAIRPORT_SYNC(shairportSyncSkeleton), "flat");
 

player.c

@@ -3432,6 +3432,9 @@ void player_volume_without_notification(double airplay_volume, rtsp_conn_info *c
  else if (config.volume_control_profile == VCP_flat)
  scaled_attenuation =
  flat_vol2attn(airplay_volume, max_db, min_db); // no cancellation points
+ else if (config.volume_control_profile == VCP_dasl_tapered)
+ scaled_attenuation =
+ dasl_tapered_vol2attn(airplay_volume, max_db, min_db); // no cancellation points
  else
  debug(1, "player_volume_without_notification: unrecognised volume control profile");
  }

scripts/shairport-sync.conf

@@ -42,6 +42,9 @@ general =
 // volume_control_profile = "standard" ; // use this advanced setting to specify how the airplay volume is transferred to the mixer volume.
 // "standard" makes the volume change more quickly at lower volumes and slower at higher volumes.
 // "flat" makes the volume change at the same rate at all volumes.
+// "dasl_tapered" is similar to "standard" - it makes the volume change more quickly at lower volumes and slower at higher volumes.
+// The intention behind dasl_tapered is that a given percentage change in volume should result in the same percentage change in
+// perceived loudness. For instance, a doubling (100% increase) of volume level should result in a doubling of perceived loudness.
 // volume_control_combined_hardware_priority = "no"; // when extending the volume range by combining the built-in software attenuator with the hardware mixer attenuator, set this to "yes" to reduce volume by using the hardware mixer first, then the built-in software attenuator.
 
 // default_airplay_volume = -24.0; // this is the suggested volume after a reset or after the high_volume_threshold has been exceed and the high_volume_idle_timeout_in_minutes has passed

shairport.c

@@ -905,9 +905,11 @@ int parse_options(int argc, char **argv) {
  config.volume_control_profile = VCP_standard;
  else if (strcasecmp(str, "flat") == 0)
  config.volume_control_profile = VCP_flat;
+ else if (strcasecmp(str, "dasl_tapered") == 0)
+ config.volume_control_profile = VCP_dasl_tapered;
  else
- die("Invalid volume_control_profile choice \"%s\". It should be \"standard\" (default) "
- "or \"flat\"",
+ die("Invalid volume_control_profile choice \"%s\". It should be \"standard\" (default), "
+ "\"dasl_tapered\", or \"flat\"",
  str);
  }