diff --git a/firmware/export/tlv320.h b/firmware/export/tlv320.h
index 75f98bc142..6c722bb437 100644
--- a/firmware/export/tlv320.h
+++ b/firmware/export/tlv320.h
@@ -26,7 +26,8 @@
 
 AUDIOHW_SETTING(VOLUME,     "dB", 0,  1, -74,   6, -20)
 #ifdef HAVE_RECORDING
- /* (x - 23)/1.5 *10 */
+/* Line in   : 0 .. 31 => Volume -34.5 .. +12 dB
+ * Mic (left): 0 ..  1 => Volume  +0,     +20 dB */
 AUDIOHW_SETTING(LEFT_GAIN,  "dB", 1,  1,   0,  31,  23, (val - 23) * 15)
 AUDIOHW_SETTING(RIGHT_GAIN, "dB", 1,  1,   0,  31,  23, (val - 23) * 15)
 /* 0 or 20 dB */