ATV demod: updated documentation

plugins/channelrx/demodatv/readme.md

@@ -103,17 +103,25 @@ Using this button you can adjust the nominal FM deviation as a percentage of the
 
 ☞ The value is accurate only with the atan2 differential demodulator i.e. FM3. With FM1 and FM2 you will have to adjust it for best image results. You can use the scope as an aid to try to fit the video signal in the 0/1 range.
 
-<h3>11: FFT asymmetrical filter toggle</h3>
+<h3>11: AM signal range correction factor</h3>
+
+This is a factor in % applied to the detected AM signal range. Because of possible overshoots the detected range may be artificially reduced from the original causing possible errors on the different detection lavels on the video signal. This control lets you correct this. Watch the video signal in the scope tab for fine tuning. It affects only AM signals.
+
+<h3>12: AM signal range offset correction factor</h3>
+
+This is a factor in % applied to the signal resulting from the previous correction and that shifts its relative position. Using this control you can position the video signal correctly so that the black level is around 0.3V. Again watch the video signal in the scope tab for fine tuning. It affects only AM signals.
+
+<h3>13: FFT asymmetrical filter toggle</h3>
 
 Use this button to enable/disable the FFT asymmetrical filter. Use this filter when you want to optimize the reception of vestigial sideband AM signals.
 
-<h3>12: FFT asymmetrical filter opposite band cutoff frequency</h3>
+<h3>14: FFT asymmetrical filter opposite band cutoff frequency</h3>
 
 For all modulations except LSB this is the lower side band.
 
 This slider lets you adjust the opposite band cutoff frequency of the FFT asymmetrical filter. The value in kHz appears on the left of the slider.
 
-<h3>13: FFT asymmetrical filter in band cutoff frequency</h3>
+<h3>15: FFT asymmetrical filter in band cutoff frequency</h3>
 
 For all modulations except LSB this is the upper side band.