diff --git a/spa/include/spa/param/props.h b/spa/include/spa/param/props.h
index 8e59e8ce2..8665013fe 100644
--- a/spa/include/spa/param/props.h
+++ b/spa/include/spa/param/props.h
@@ -59,13 +59,16 @@ enum spa_prop {
 	SPA_PROP_START_Audio	= 0x10000,	/**< audio related properties */
 	SPA_PROP_waveType,
 	SPA_PROP_frequency,
-	SPA_PROP_volume,				/**< a volume (Float), 0.0 silence, 1.0 normal */
+	SPA_PROP_volume,			/**< a volume (Float), 0.0 silence, 1.0 no attenutation */
 	SPA_PROP_mute,				/**< mute (Bool) */
 	SPA_PROP_patternType,
 	SPA_PROP_ditherType,
 	SPA_PROP_truncate,
-	SPA_PROP_channelVolumes,		/**< a volume array, one volume per
-						  *  channel (Array of Float) */
+	SPA_PROP_channelVolumes,		/**< a volume array, one volume per channel
+						  * (Array of Float). 0.0 is silence, 1.0 is
+						  *  without attenuation. This is the effective volume
+						  *  that is applied. It can result in a hardware volume
+						  *  and software volume (see softVolumes) */
 	SPA_PROP_volumeBase,			/**< a volume base (Float) */
 	SPA_PROP_volumeStep,			/**< a volume step (Float) */
 	SPA_PROP_channelMap,			/**< a channelmap array
@@ -74,9 +77,11 @@ enum spa_prop {
 	SPA_PROP_monitorVolumes,		/**< a volume array, one volume per
 						  *  channel (Array of Float) */
 	SPA_PROP_latencyOffsetNsec,		/**< delay adjustment */
-	SPA_PROP_softMute,			/**< mute (Bool) */
-	SPA_PROP_softVolumes,			/**< a volume array, one volume per
-						  *  channel (Array of Float) */
+	SPA_PROP_softMute,			/**< mute (Bool) applied in software */
+	SPA_PROP_softVolumes,			/**< a volume array, one volume per channel
+						  * (Array of Float). 0.0 is silence, 1.0 is without
+						  * attenuation. This is the volume applied in software,
+						  * there might be a part applied in hardware. */
 
 	SPA_PROP_iec958Codecs,			/**< enabled IEC958 (S/PDIF) codecs,
 						  *  (Array (Id enum spa_audio_iec958_codec) */