Why do the controls on modern digital electronics have such a LOOONG lagtime?

The recent hulaboo about the switchover to digital TV meant that I had to do some serious buttonpushing the other day. To add to any other frustrations in the process, I had to deal with the lagtime on the controls. You push a button, and maybe two-three seconds later you finally get the result. If you push too many buttons too fast, the controller chip locks up :mad: Why the #%!! does this take so long?

I’m no techie, but my son says that sometimes it’s the cables, the power cords, whatever they’re called. He put different ones on my DVD player and now I don’t make breakfast while waiting for a DVD to load.

My TV does this, and I hate it. Change the channel, and you’ve got to wait for it to appear, and none of the remote buttons do anything in the meantime. No way to hit the “up channel” button three times in succession, to go three channels up. The thing is, in the “channel edit” mode, you can scroll through the channels quickly, so it’s physically capable of doing it, it just isn’t programmed to. Actually, there are so many crappy usability issues with how the remote works, I couldn’t even list them all.

For a slightly more technical answer it has to do with the difference between analog and digital video transmission as well as the requirements for demodulating them. An analog TV can tune the picture instantaneously because the image being displayed is presented line-by-line at very high frequencies. As soon as the tuner has the right frequency the picture can be rastered.

A digital video signal requires some form of encoding which generally involves only transmitting the changes between the previous frame and the current one. It can take some time to finally get enough data to display an image. When you add in audio syncing and other issues (multiplexing, encryption) it can take noticeable periods of time before a digital video signal can be sent to your TV for display.

Additionally, since decoding these digital streams is more computational intensive than analog TV (which really has no computation at all) the set-top boxes generally become unresponsive while attempting to tune the selected channel. No more “channel surfing”…

Now if your issue was with configuring the box and unresponsiveness in setup menus (while no picture was displayed) then they probably just used a microcontroller that was significantly underpowered for what it needed to do.

Because building them with a shorter lag time won’t sell any more units.

It’s not something most people compare when choosing a TV etc. And people generally don’t even get to choose a cable box, they take whatever the cable company gives them.

Same reason why the user interfaces on most firmware and software suck so much. People generally don’t return electronics or software and complain to the company and demand a refund because the UI sucks.

Jas09 is pretty much right. Digital video decoding is much different than analog.

Interestingly, I have AT&T U-Verse–digital “IPTV”, basically they hook me up with a 35Mb DSL connection, part of which is reserved for streaming TV. Channel-changing on this system is quite instantaneous.

PatriotGrrrl, the only reason Tivo clings to life is that there are quite a few people who will pay exhorbitant, unnecessary, and outlandish prices just to have a UI that doesn’t suck.

I think that part of this is because they are only streaming one “channel” at a time which eliminates the tuning/multiplexing part of the equation. It’s also possible they are using a faster decoder chip in their box. (As an aside, if you have HD, how is the picture quality? - that’s been my main hesitation in getting U-Verse).

PatriotGrrrl makes a good point too and one I’ve seen play out with my cable company. Our previous Moxi cable DVR box had an extremely slow interface. They pushed a new software patch that was much more responsive (certainly in response to user complaint). Unfortunately, the increased processing load caused the boxes to overheat and shut down. Now the “new, improved” Moxi’s are out and have the old slow interface (but no heat problem - they just slowed down the processor).

Responsive menus just isn’t normally something people will change companies for. Completely failed units is.

So, by definition, not unnecessary.

Jas09’s answer is correct, but there can be other delays. Digital cable networks are implemented using multicast. There can be significant delays in joining a multicast, as the routers need to negotiate. On some systems, when you change channel it actually starts out with a unicast connection, switching over to the multicast when the packets start arriving.

To expand on this, if quick channel surfing was a requirement of digital TV it would be possible to deliver it, but only by reducing the compression ratio. That would mean fewer channels.

Tivo prices are neither exorbitant nor outlandish, but then I also don’t think Apple computer prices are, either.

>A digital video signal requires some form of encoding which generally involves only transmitting the changes between the previous frame and the current one.

I dont think this is the issue. The key frame comes up pretty often (several times a second) unless the person happened to tune into a still frame. I also dont think ATSC uses a codec that works like this.
The box I bought for my kitchen doesnt have a 3 second delay. I suspect the real problem here is the underpowered CPUs in these embedded devices. The manufacturer can save a few bucks by selling you this unit. I bet theres a lot of pressure to keep the selling cost around $40 so people can just buy it using the government coupon. The box has the added work of taking the HD signal and scaling down to your TV’s added resolution.

At the end of the day there’s no real reason why this cant be sped up. Its just digital video processing. My directv box is fast too. It wont be as fast as your typical analog box, but it should be a lot better than waiting 3 seconds between changes. Next time, read the reviews of the products you intend to buy.

I have a digital TV in one room and an analog in another room. When viewing the same program the digital TV lags the analog by a few seconds. It seems to me it is the time needed for decoding the signal.

It’s unnecessary, IMO, for them to charge as much as they do (especially the per-month charges). I love their software, but have problems with their business plan, which I think is killing them. With the feature set their DVR offers, and the complaints I see from all other providers (cable co.s, AT&T, Dish, and DTV), the adoption rate of Tivo boxes would be astronomical if they didn’t have such ridiculous monthly pricing. People constantly complain about their DVR software, but it’s not worth an extra $20/month (plus up-front equipment costs).

Are you sure about this? I thought key frames were sent every second or so, although I can’t find a cite for this. If they are that frequent, you’re right that processing delays are most likely to blame. Could be a lack of horsepower, or just inefficient coding.

In MPEG-2, which is used by ATSC, there are 3 types of frames - I, B, P. An I(ntra)-frame is the only type which contains enough info to display by itself. A P(redicted)-frame contains changes from the previous I or P frame, and a B(i-directional) frame is contains changes from both the previous and next I or P frame. You generally get an I-frame twice a second. So if you’re very unlucky, you may have to wait for 14 frames at 30 frames/sec = 0.46 seconds before you get the first I-frame. But it’s a little worse than that - you have to buffer up at least a few frames before you can start actually streaming video - you might have a series of frames that looks like I-B-B-P - and you can’t display the second frame (a B-frame) until you’ve got the following the P frame. So there are some delays there as well - 3 more frames worth. They get around this by rearranging the transmission order a bit, but that really doesn’t save you more than a frame or 2 in time.

It’s $12.95/month, and that’s the absolute maximum. Pre-pay for a year or two and you’ll get a big discount. And now that lifetime subscription is back, you can choose to pay up front and never pay again. And even at $20, I’d pay it and smile. Neither Fios nor Cablevision’s DVR’s were even close in ease of use and response time.

To this you have to add whatever processing time is required.

But in my converter box I can hit “Up channel” five times and it will go up five channels without attempting to actually tune in to each one.

It takes a while to get used to the delay but after a while you get used to it and act accordingly.

The simple answer is: because old electronics were purpose-built, simplistic designs and today’s electronics are more like simplified generalized computers, so you have to deal with slow software and processors…

Well, no, how fast you can scroll through the channels is independent of the display lag. If you’re going faster than the display lag, it just won’t have time to display. Also, see my post in the second reply.

I can receive the same network from multiple stations, and often one will be delayed relative to the other. Most recently, watching the NHL finals “live”, the Lansing station was a couple seconds ahead of the Detroit station (both HDTV). The CBC station (through cable) was another two or three seconds ahead of the Lansing station. There’s certainly some encoding/decoding time, but you can’t really judge how much it is based on the digital Vs. analog delay.