I'm a stickler for image quality in my high-def TV and video game viewing. One of the things that bugs the living shit out of me, and that no one else seems to notice, is the problem of Y/C delay.

For the uninitiated, Y/C delay is a discrepancy between the luminance portion (the black-and-white portion) of a video signal and the corresponding chrominance (color or hue information) of a video signal.

On high definition equipment, the picture is usually carried over a component video cable, also known as a YPbPr video cable. It has three wires:
Y - Luminance signal only
Pb - Blue chrominance signal
Pr - Red chrominance signal
(The green chrominance signal is matrixed together on the Pb and Pr wires.)

Every. Single. Piece. of component video playback equipment I own (Tivo, DirecTV DVR, DVD, game consoles, etc.) has a differing amount of Y/C delay error. This seems to be a common bug in the video output circuits of most consumer gear.

I couldn't find a good "real" picture of what Y/C delay looks like, so I photoshopped up a couple of images that simulate the difference between a correct image and an image with some Y/C delay inserted. Those images should be attached to this message, have a look below to see what I'm talking about. It's not exactly realistic, but it gives you the idea.

The solution is to delay the signal on the necessary wire. Depending on the direction of the misalignment, and which channels are affected, you might have to delay the signal on any one, or possibly any two, of the three wires in the component video connection.

I have, up until now, performed this trick by using a large loop of coaxial video cable, inserted in the video signal chain at the appropriate spot between the player and the TV and/or switchbox. It turns out that the delay in question is only on the order of fractions of a microsecond, and that as little as 50-75 feet of coax cable is enough to fix the problem.

But this is hugely ungainly, and results in gigantic wire coils in the jungle behind my AV rack, in a place that needs more wires like I need a hole in the head.

I'd like to locate, or devise and construct, a very small (as small as possible) and inexpensive box that performs the exact same task as my gigantic (but inexpensive) coax loops currently perform, thus making my life easier when I go spelunking back there. It would need to be small enough so that I could connect multiple boxes to the various wires to compensate for different amounts and different kinds of Y/C delay present on my plethora of video devices.

In terms of locating something that already exists, Google has found one or two professional video devices that do this, but they are expensive and large and part of a larger system. Not what I want.

Is this something that can be done with a simple electronic circuit, or must a long coil of wire be involved?

If a long coil of wire must be involved, I've seen some electronic devices that involve very thin wire coils in radios and power supplies, for example, a tiny copper wire coiled around a magnet, or wires coiled together in a power transformer. Can something like this be modified for this task, do you think, or would there be significant wire-resistance issues or R/F interference issues?

Anyone have experience in this, or can offer advice?

Mmm.. the longer term solution for you should be to gradually switch everything over to a digital feed (eg. DVI-D or HDMI).

Analog interconnect is dying out quickly, thank goodness!

Agreed. But not all of the devices I own have that capability, and I'd like to do something about it now.

I presume your examples are exaggerated. A simple delay line on the leading signal(s) should sync everything. A box like this should do the trick. Bear in mind you could end up with up to 2 on each source. That could get expensive very quickly.

We used to use them to time in bits of analogue kit in studios that didn't have enough internal adjustment. Since everything went SDI and framesyncs got cheaper it's less of an issue.

Of course dialling in delay will soften the picture. There's very little consumer HD component kit in the UK thank goodness.

Although my example is hand-made instead of an actual screen shot, the amount of delay is not exaggerated. Keep in mind that's a fairly large magnification of a Tivo menu screen. But the amount of "smear" relative to the size of the graphics is about right.



Yeah, that's more like what I'm looking for. But even smaller and cheaper than that. Do you (or anyone else) know what is going on (electronically) inside that box?



Using the coiled-cabling trick, I've found that it does not soften the picture at all, each delayed signal is just as sharp as if I hadn't delayed it at all. And since it fixes a color smearing problem, the result is a *sharper* picture.

If you can calculate the delays yourself then you could just buy some PCB mount fixed delays from the same manufacturer. That should be considerably cheaper.

Lots of wire coiled up most likely......

Have you checked whether there is an engineering sub-menu on your TV/display that can correct for this? My Sony TV has consumer menu presets for (e.g.) default audio boost/attenuation on an input-by-input basis so I don't think it is beyond the realms of possibility that there's a (doubtless *very* terse) engineer menu that might be of help to you.

Might be worth punting this out on AVForums in the pretext of accessing the engineering menus?

Absolutely, it's something I look for on every device. It is rare to find except on the most tweakable of devices.

But even when I had a television set with an adjustable Y/C delay, it was only settable uniformly across all inputs. Whereas my playback devices were all different in the amount and type of delay. So with that TV set I had to do an interesting dance where I compensated for one device with the TV settings, and then compensated for another device with the coax coils.

While I'm not wishing to state the bleedin' obvious, have you checked for the presence of 'engineering' menus on all of your playback devices?

Should that be "in" or "on" or was I so grammatically incorrect that none of the above was applicable?

Absolutely, it's something I look for on every device.

Y/C delay control is incredibly rare on any device. There are a few that have it, but none of my current devices have it that I've been able to find.

Hi.

This is an article explaining how an active analog delay can be produced in a simple way using an op-amp. You would need an op-amp with a bandwidth of at least twice the maximum frequency you were trying to pass through it.

pca

Though that only works for delays smaller than the pixel time, right? Its output depends only on the input voltage and the capacitor charge, which isn't enough "memory" to remember several pulses. If so, and if Tony's images showing delays several pixels long are a true depiction of the problem, this circuit won't help.

Peter

That's absolutely true, the delays are at least several pixels.