modern TVs and composite video

[NY]

I would say that "analogue" and "digital" *can* be applied to tuners. Obviously the input is always analogue signals in a UHF channel. But "analogue" and "digital" relate to the signal processing that the tuner carries out - does it demodulate an analogue-TV signal using vestigial-sideband AM and produce an analogue output (composite video); or does it decode a digital-TV signal using COFDM and produce an MPEG data stream?

It is surprising how many modern TVs still include an analogue-TV tuner - sometimes it is the only way of injecting an analogue-TV signal from an old device such as a VHS recorder/player. Given a TV *has* analogue-TV input, it is a shame that it does not also have a baseband analogue (eg SCART) input for devices that have no RF tuner but only baseband analogue output. We have an old digital-TV HDD recorder which has SCART but no modulator, so our modern TV cannot play anything on it (legacy recordings). I've already copied off (using an analogue-TV digitiser) some recordings so they are in MPEG=TS format, but anything else can only be played on an old TV which is old enough to have analogue input.

But this is a problem which will gradually go away as fewer analogue-output devices remain with legacy recordings on them.

[Dave Plowman (News]

I'd read that. But here, at least, I've more success with DVI than HDMI as regards a KVM switch (video only, and no VGA used) on these computers. And it's an expensive business, experimenting.

[Dave Plowman (News]

I think most simply extract the mixed blanking from the composite?

[NY]

Given that it is possible to buy DVI-HDMI cables and adaptors with no active components (and maybe no passive resistor networks either) I presumed that DVI and HDMI were near-enough identical signals.

[Steve Walker]

I am pretty sure that HDMI is simply a superset of DVI-D.

[NY]

Also you can get VGA to DVI adaptors if a PC has one output and a monitor has a different input, and those are passive. I'm not sure whether VGA signals have the same bandwidth or whether a given resolution by VGA connector is a little more blurred because of poorer HF response. So it may be that VGA is a subset of DVI which is a subset of HDMI, in terms of being able to connect PC to monitor by simple cable.

My monitor has VGA, DVI and HDMI inputs (one of each) so I have three different computers connected to it. My main Win 7 PC is DVI, a Linux PC is VGA and the HDMI is free for if I ever need to connect a Raspberry Pi directly to the monitor as opposed to using VNC client on the Win 7 PC to access the Pi desktop.

OK, I could have got a KVM switch and multiplexed several computers into a single monitor input, then I wouldn't have needed a separate keyboard and mouse for the Windows and Linux PCs.

[Andy Burns]

I think so as far as DVI-D is concerned, but generally DVI doesn't carry audio (HDMI carries it in the blanking intervals, but DVI kit won't see it or insert it).

[Steve Walker]

There are three versions of DVI - DVI-D, DVI-I and DVI-A.

D is purely digital and is what HDMI was taken from. The connector has sufficient pins for DVI-D to carry signals for two monitors (or one very high res one) as two completely separate channels.

A is analogue and copes with VGA signals and the like. DVI-A has only analogue signals.

DVI-I has one set of digital and one set of analogue pins, allowing a graphics card to drive digital or analogue monitors (or both at once).

I use both HDMI ports on mine (one for my PC and one for my work laptop), keeping VGA free for any odd item I might need to connect. I have no use for the two Display Port inputs that remain.

I switch the keyboard between my PC and the work laptop with a USB switch, switch the monitor over with its own selection buttons and leave a mouse connected to my PC and a trackball to the work laptop - a USB switch being a lot cheaper than an HDMI KVM.

[Dave Plowman (News]

Thing is the signal may be the same, like for like, but the electronics processing that signal different? There are after all different versions of HDMI.

[Andy Burns]

You'd probably be limited to single-link connections, so no silly high resolutions or refresh rates or bits per pixel.

[Dave Plowman (News]

I remember trying to get a spare 'HD ready' TV with a single HDMI socket to work with a PC and Acorn computer and HDMI KVM switch (audio not needed)

It did work from the PC HDMI if you chose the correct screen resoltion - which would be Ok for this purpose. But never got the Acorn VGA + VGA to HDMI adaptor working regardless of being able to make any monitor definition file on the Acorn. Nor did the VGA to HDMI adaptor work using the PC VGA output - even fed direct to the TV.

[Andy Burns]

Was that the ex-mining rig GPU, or a different one?

Like you, I used to use DVI+PS/2 KVM; but that got a bit too old-hat to support newer laptop and monitor resolutions, so I leapfrogged over HDMI to DP.

So I have linux box and laptop docking station on KVM, with an active VGA to HDMI dongle on a different monitor input for the occasional "other" machines I need to hook up, all works ok, both the DVI an DP KVMs have been from Aten, who do seem to fix bugs in their firmware, Actually I wish they made a 4 input version of what I have.

[Dave Plowman (News]

No - some time before that, and a different PC/RPC combination.

All my KVM switches have been Aten.

On the problem setup, I 'solved' it by buying a computer monitor with both VGA and HDMI inputs. And have to swap them on the monitor. The KVM switch merely doing the keyboard and mouse.

The setup with this pair is DVI and works just fine - this monitor not going to super resolutions.