Add a speaker-dist config option

This can be used to specify an average speaker distance without having the
modify the decoder config files. This also sets a default value of 1, letting
near-field effects work (if imprecisely) without an explicitly-configured
distance.

2 files changed, 29 insertions, 21 deletions

diff --git a/alc/panning.cpp b/alc/panning.cpp
index d0afd577..32ccd080 100644
--- a/alc/panning.cpp
+++ b/alc/panning.cpp
@@ -611,10 +611,16 @@ void InitPanning(ALCdevice *device, const bool hqdec=false, const bool stablize=
                 { return BFChannelConfig{1.0f/n3dscale[acn], acn}; });
             AllocChannels(device, count, 0);
 
-            float nfc_delay{device->configValue<float>("decoder", "nfc-ref-delay").value_or(0.0f)};
-            if(nfc_delay > 0.0f)
-                InitNearFieldCtrl(device, nfc_delay * SpeedOfSoundMetersPerSec, device->mAmbiOrder,
-                    true);
+            float avg_dist{};
+            if(auto distopt = device->configValue<float>("decoder", "speaker-dist"))
+                avg_dist = *distopt;
+            else if(auto delayopt = device->configValue<float>("decoder", "nfc-ref-delay"))
+            {
+                WARN("nfc-ref-delay is deprecated, use speaker-dist instead\n");
+                avg_dist = *delayopt * SpeedOfSoundMetersPerSec;
+            }
+
+            InitNearFieldCtrl(device, avg_dist, device->mAmbiOrder, true);
             return;
         }
     }
@@ -1016,11 +1022,13 @@ void aluInitRenderer(ALCdevice *device, int hrtf_id, al::optional<StereoEncoding
                     spkr_count += 1.0f;
                 }
             }
+
+            const float avg_dist{(accum_dist > 0.0f && spkr_count > 0) ? accum_dist/spkr_count :
+                device->configValue<float>("decoder", "speaker-dist").value_or(1.0f)};
+            InitNearFieldCtrl(device, avg_dist, decoder.mOrder, decoder.mIs3D);
+
             if(spkr_count > 0)
-            {
-                InitNearFieldCtrl(device, accum_dist / spkr_count, decoder.mOrder, decoder.mIs3D);
                 InitDistanceComp(device, decoder.mChannels, speakerdists);
-            }
         }
         if(auto *ambidec{device->AmbiDecoder.get()})
         {
diff --git a/alsoftrc.sample b/alsoftrc.sample
index f2b17982..4ea548ce 100644
--- a/alsoftrc.sample
+++ b/alsoftrc.sample
@@ -305,22 +305,22 @@
 ## nfc:
 #  Enables near-field control filters. This simulates and compensates for low-
 #  frequency effects caused by the curvature of nearby sound-waves, which
-#  creates a more realistic perception of sound distance. Note that the effect
-#  may be stronger or weaker than intended if the application doesn't use or
-#  specify an appropriate unit scale, or if incorrect speaker distances are set
-#  in the decoder configuration file.
+#  creates a more realistic perception of sound distance with surround sound
+#  output. Note that the effect may be stronger or weaker than intended if the
+#  application doesn't use or specify an appropriate unit scale, or if
+#  incorrect speaker distances are set. For HRTF output, hrtf-mode must be set
+#  to one of the ambi* values for this to function.
 #nfc = false
 
-## nfc-ref-delay
-#  Specifies the reference delay value for ambisonic output when NFC filters
-#  are enabled. If channels is set to one of the ambi* formats, this option
-#  enables NFC-HOA output with the specified Reference Delay parameter. The
-#  specified value can then be shared with an appropriate NFC-HOA decoder to
-#  reproduce correct near-field effects. Keep in mind that despite being
-#  designed for higher-order ambisonics, this also applies to first-order
-#  output. When left unset, normal output is created with no near-field
-#  simulation. Requires the nfc option to also be enabled.
-#nfc-ref-delay =
+## speaker-dist:
+#  Specifies the speaker distance in meters, used by the near-field control
+#  filters with surround sound output. For ambisonic output modes, this value
+#  is the basis for the NFC-HOA Reference Delay parameter (calculated as
+#  delay_seconds = speaker_dist/343.3). This value is not used when a decoder
+#  configuration is set for the output mode (since they specify the per-speaker
+#  distances, overriding this setting), or when the NFC filters are off. Valid
+#  values range from 0.1 to 10.
+#speaker-dist = 1
 
 ## quad:
 #  Decoder configuration file for Quadraphonic channel output. See