Tell me what I am missing.

My understanding is that a 1080p 120Hz screen will require the full 3.4gbps specification for the HDMI 1.3 standard for 8 bit color. As far as I know,, the fastest commercially available silicon is 2.25gbps. Yet, they are selling 1080p 120Hz TVs at Best Buy.

Am I missing something? Are these TVs less than 8 bit color?

There are no commercial devices that will send out a 120Hz signal (except PC's). BluRay, HDTV, PS3, etc. all send out 24/30/60Hz. Not to mention that the TV is actually displaying 120Hz, not the device.

You don't need a special cable for 1.3a or 120Hz. www.monoprice.com and www.bluejeanscable.com sell cables that meet the 1.3a spec.

Thank you for the prompt response.

So, if there are no commercial devices that can send out a 120Hz signal, what is the point of having a 120Hz refresh rate?

Since the silicon is usually developed as both transmitter and receiver pairs, I would think that if they cannot send a 120Hz signal, then nor can they receive it either. In that case, how can a TV be 1080p 120Hz? What am I missing?

For what it's worth, Silicon Image is the dominant supplier of HDMI silicon. They offer chips with a maximum throughput of 6.75gbps. Apparently, this is quite difficult stuff. There is a small company out there, TranSwitch, that has 10.5gbps throughput that allows for the full use of the 1.3 standard. I am trying to figure out when it will be a requirement to have the higher throughput. It would seem to me that 1080p 120Hz televisions would require that higher throughput but apparently not so. Can you explain why not?

TIA

So, if there are no commercial devices that can send out a 120Hz signal, what is the point of having a 120Hz refresh rate?

I believe the only purpose is to reduce the apparent latency. Latency tends to be a problem with LCD, and my understanding is that it can be reduced somewhat by more frequent rewriting to the screen.

Since the silicon is usually developed as both transmitter and receiver pairs, I would think that if they cannot send a 120Hz signal, then nor can they receive it either. In that case, how can a TV be 1080p 120Hz? What am I missing? ?

The 120Hz is strictly the TV's internal refresh rate. It cannot receive a 120Hz signal.



For what it's worth, Silicon Image is the dominant supplier of HDMI silicon. They offer chips with a maximum throughput of 6.75gbps. Apparently, this is quite difficult stuff. There is a small company out there, TranSwitch, that has 10.5gbps throughput that allows for the full use of the 1.3 standard. I am trying to figure out when it will be a requirement to have the higher throughput. It would seem to me that 1080p 120Hz televisions would require that higher throughput but apparently not so. Can you explain why not?

The data rate depends on three things: resolution, frame rate, and color depth. If the signal were 120Hz, which it is not (and never will be; nobody shoots at anywhere near that frame rate, so it'd be a huge waste of bandwidth), then it would need double the bitrate of a 60Hz signal. A 1080p signal, at 60 frames/sec and 8-bit color depth, requires 1.485 Gbps per channel (the 10.5 you're referring to actually is too high; the highest rate currently supported by the spec is 10.2; and that's an additive rate, covering all three color channels, the actual rate being 3.4 Gbps). If you went to 120 Hz on the actual signal on that 1080p, it would get close to the 3.4 Gbps top bitrate, at 2.97 Gbps.

Anyhow: the answer, of course, as to why that full bitrate isn't required for a 120Hz signal is, as stated above: it's an internal refresh rate, not a rate at which the signal flows.

Kurt
Blue Jeans Cable (http://www.bluejeanscable.com/store/hdmi-cables/index.htm)

Thank you.