2 audio filters added, a volume-dependent-loudness and a convolution filter.

scripts/shairport-sync.conf

@@ -35,6 +35,36 @@ general =
 //	interface = "name"; // Use this advanced setting to specify the interface on which Shairport Sync should provide its service. Leave it commented out to get the default, which is to select the interface(s) automatically.
 };
 
+
+dsp =
+{
+
+//////////////////////////////////////////
+//  This convolution filter can be used to apply almost any correction to the audio signal, like frequency and phase correction.
+//  For example you could measure (with a good microphone and a sweep-sine) the frequency response of your speakers + room,
+//  and apply a correction to get a flat response curve.
+//////////////////////////////////////////
+//
+//  convolution = "yes";                  // Activate the convolution filter.
+//  convolution_ir_file = "impulse.wav";  // Impulse Response file to be convolved to the audio stream
+//  convolution_gain = -4.0;              // Static gain applied to prevent clipping during the convolution process
+//  convolution_max_length = 44100;       // Truncate the input file to this length in order to save CPU.
+
+
+//////////////////////////////////////////
+//  This loudness filter is used to compensate for human ear non linearity.
+//  When the volume decreases, our ears loose more sentisitivity in the low range frequencies than in the mid range ones.
+//  This filter aims at compensating for this loss, applying a variable gain to low frequencies depending on the volume.
+//  More info can be found here: https://en.wikipedia.org/wiki/Equal-loudness_contour
+//  For this filter to work properly, you should disable (or set to a fix value) all other volume control and only let shairport-sync control your volume.
+//  The setting "loudness_reference_volume_db" should be set at the volume reported by shairport-sync when listening to music at a normal listening volume.
+//////////////////////////////////////////
+//
+//  loudness = "yes";                     // Activate the filter
+//  loudness_reference_volume_db = -20.0; // Above this level the filter will have no effect anymore. Below this level it will gradually boost the low frequencies.
+
+};
+
 // How to deal with metadata, including artwork
 metadata =
 {