scan rate settings

[adder]

hey again so i've been getting on with setting up and configuring groovymame (magic resolutions) with my crt scart tv.
i have been tweaking the vertical size and position via the tv service menu.
what i have found is, regarding the scan rate settings in mame.ini, which i had originally set as:

crt_range0  15625-16400...

what i get using those numbers is, for example 240p games such as rastan, gauntlet, etc, i have some problems with the top and bottom of the image being cut off, regardless of how i tweak the vertical size/position settings in my tv service menu (see the first picture below).

however, if i set the scan rate settings in mame.ini as follows:

crt_range0  16400-16400...

first impressions are i seem to get better results (no lines missing, see second pic below).

my question is, am i actually ok to just leave the crt_range0 line as '16400-16400' or am i now limiting the room groovymame has to work with so to speak (ie. am i likely to run into problems later/have problems with other resolutions always being forced to use a 16400 scan rate?)

many thanks for any advice!

crt_range0  15625-16400...



crt_range0  16400-16400...

[Calamity]

Using 16.4 kHz can be a bit overkill for resolutions that would otherwise just require 15.7 kHz. What you're doing is adding a huge amount of padding lines up and down. Probably these increased borders are helping to "compress" the active video so that it fits the screen (it's not usual to be able to trick a CRT this way). However, honestly I don't see such a big difference between both pictures.

To answer your question, no, you're not limiting GM by doing so, as long as you pick the upper hfreq value to create a narrow range. You'd be limiting it if you had picked the lower value (15.7-15.7). Indeed, you'll get more consistent horizontal size if you use a narrow hfreq range (notice how hfreq affects the width: your second picture is narrower horizontally).

That said, even if the TV seems to accept 16.4 kHz happily, always keep in mind these things are supposed to work at 15.7 kHz. So you're doing this at your own risk.

[adder]

ah ok thanks for that i will have another look at it and perhaps make some changes. the tv is ok at 16.4khz, but does not like 16.5khz (picture becomes erratic). i do have a second tv also so might give that a go and see how that one performs. i've thrown all sorts of odd modelines at the current tv im using; it's been a kind of 'test subject' and its had to put up with all sorts of experiments. ive had it make whistling noises in the past when the scan rate was too high, and once im sure i smelt burning (it might have just got hot and had some dust etc burn on the chassis perhaps, who knows! )
cheers!