I have Comcast digital cable service with a cable box. When I change channels with the up/down arrow buttons on the remote, it takes a full two seconds to resolve the new channel. Our second TV has no cable box (basic cable channels only), but it changes channels much faster.
Why is digital cable service slower?
That has been my experience with a digital converter box as well. Basic cable with no box uses the TV’s tuner and you can rapidly move up and down the channels. A digital box needs time to load each channel so it takes a couple seconds to click form one to another. You almost have to use the menu to scan the program line up rapidly.
I also have Comcast, and I’ve had the same experience. It’s easier to use the menu to decide what to watch than to flip through the channels.
Yes that is the one bad thing about digital it has to read the 0s and 1s and convert them to a picture.
Sometimes it takes up to 30 seconds to register anything I’m doing, I have Comcast too. It’s like it freezes up, but I guess it IS a computer and since I leave it on all the time, it’s bound to have problems.
Analog cable is sent in a format that your television already understands – “broadcast” modulated video that simulates over-the-air television channels. Changing between channels is instantaneous because all the channels are already in a format that can be shown “instantly” by your television.
Digital cable beams a digital (duh) stream of MPEG audio and video to your locale. Your local hardware, the cable box, needs to buffer some small portion of a second of video/audio before it can begin displaying the signal. That 2-4 second delay is basically the MPEG decoder chips having a slight heart-attack when the stream changes, and resynchronizing to the new signal and buffering up enough video and audio to start playing back the new channel.
Having said all that, digital cable and satellite completely suck for people like me who used to channel-surf to find something interesting to watch on TV. The benefits of digital TV mostly outweigh that negative, but the cable and satellite providers could certainly fix this problem (perhaps by pre-buffering adjacent channels) and make the experience snappier.
The problem is a side-effect of the compression used for digital television. Analog television sends a complete image, 30 times a second. Digital television cheats by not sending very many complete images. Most of the time, it just sends information on what has changed since the last image. This means if the channel is changed, it has to wait until a complete image is transmitted, which can take a while. Uncompressed digital television is used inside the television studio, but the bit rate is far too high for transmission to the affilliate stations or the end users. An uncompressed signal is about 1.4 billion bits per second. Compression reduces that to 19 million bits per second or less.
On other sites, I’ve read that channel changes & the like (basically anything but the power button) are sent back to the headend (i.e. the cable company) where it is processed somehow and then sent back to the box. That could add a bit of delay, especially if the processing is slowed down by improperly configured or poorly maintained databases on the headend; I could easily imagine a cable operator skimping on DB maintenance to improve the bottom line.
I have no idea if that’s true or not, but it’s certainly one way that they can handle things like on-demand programming, where you can pause, rewind, and fast-forward. Of course, this also allows the cable company to know exactly what you’re watching, but I’m sure they wouldn’t be interested in that. 
FWIW, I’m on Charter, but we use the same boxes (and as I understand it, the same headend equipment) as Comcast, and I don’t see much of a delay – well under a second, even on HD channels where you’d expect a much higher bandwidth signal and higher signal-processing overhead on the box.
I’m on Charter, too, and I see no delay. In fact.I tried to time it, and as best as I could see, it took less than 1 second.
What’s more my DVR’s on the blink. Can’t record or even play previous recordings and Cable Guy won’t get here until Thursday.
I’ve had both Time Warner and Cincinnati Bell digital TV and there is a slight (1-3 second) delay. It’s noticeable if you have an analog connection and a digital connection going at the same time.
I have Comcast cable and I recall that my service was pretty instantaneous…until I got Tivo service. With a DVR you are always recording what you’re watching so you can rewind. So you’re now watching what has been recorded and it takes a second or so to see this. Maybe those of you who are experiencing the delay have DVR service?
If you have DVR service, try fast forwarding. When you have used the rewind or pause feature and change channels, the channel changes in the present, but you are still watching what happened in the past. 
That’s a problem with the Comcast box-- we call it “remote stutter”. It drives me insane sometimes.
No DVR here.
Nor here. I have two analog cable-ready TV’s and one with the box (for On Demand, etc.). Definitely a difference.
It’s not just cable. Digital satellite has the same issue on changing channels.
I don’t think that’s actually the case on most cable systems. They’re sending out every channel all the time, and it’s just the lag on decompressing and/or unencrypting the signal that causes the channel change to go so slowly.
I do think there’s some service (AT&T Uverse?) that does do it the way you mention (they just send the channels you’re watching at that time) but not Comcast or Time Warner or whoever. Well, other than when you use OnDemand.
Its all the GOP’s fault. No, really - a GOP is the basic unit of MPEG video, so the stream decoder has to start decoding at the start of a GOP. GOPs are usually 1/2 second of video, so a decoder needs to wait a medium time of 1/4 second to get to the next GOP boundary, and then start decoding.