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Discussion Starter · #1 ·
This was motivated by a thread in the DVD forum. I was questioning whether it was worth getting an HDMI capable DVD player if my Sony 42WE655 internally converts the HDMI to analog and then back to digital for display purposes.


But now the analog concept is being questioned. I thought that it was well known that some TVs like these Sonys do that. Does anyone know for sure and, if so, what is the source of that information.


Ed
 

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Coyote Waits
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Quote:
Originally Posted by ekb
This was motivated by a thread in the DVD forum. I was questioning whether it was worth getting an HDMI capable DVD player if my Sony 42WE655 internally converts the HDMI to analog and then back to digital for display purposes.


But now the analog concept is being questioned. I thought that it was well known that some TVs like these Sonys do that. Does anyone know for sure and, if so, what is the source of that information.


Ed
I have read reports from engineers who have used schematics from FCC filings to determine that the 2003 RCA DLP sets and the 2004 Mitsubishi DLP sets do convert DVI/HDMI to analog for video processing.


I've read similar reports that the Samsung sets have always been digital all the way to display.


I don't know anything about later RCA sets or the new Mitsubishi. I've heard that the Panasonic DLP sets are all digital and that Toshiba DLP sets are not.


LCD sets like Sony's have an analog stage. I haven't followed them closely so that is just an impression.


In the case of DLP sets I think using an analog stage for all external inputs is a cost saving measure. Or, it may have been done to get to market faster.
 

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Discussion Starter · #3 ·
Thanks for the info.


Do you think there is a relatively easy way/test to determine which sets convert to analog and which don't?


Ed
 

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Quote:
Originally Posted by ekb
Do you think there is a relatively easy way/test to determine which sets convert to analog and which don't?
The original RCA DLP couldn't accept 720p as input through DVI. That was a big clue.


As for the others, I would check out threads devoted to them and see if anyone has had a chance to check a schematic. The Samsung threads have a few people who do that on a regular basis.
 

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The Sony LCDs convert the HDMI digital signal to analog.
 

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LCDs do not require an analog stage.


The only display tech that needs an analog stage is CRT.
 

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Discussion Starter · #7 ·
Quote:
Originally Posted by BillP
The Sony LCDs convert the HDMI digital signal to analog.
Yes - that's what we think we know. But I'm looking for something more substantial as evidence.


Ed
 

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The statement was made by one of the respected members here (I believe it was uzun), based on the schematics of the Sony.
 

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Originally Posted by rogo
LCDs do not require an analog stage.


The only display tech that needs an analog stage is CRT.
They may not require it, but it's apparently cheaper to make it that way, and Sony apparently cut corners.
 

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Discussion Starter · #10 ·
Quote:
Originally Posted by rogo
LCDs do not require an analog stage.


The only display tech that needs an analog stage is CRT.
Agreed. But nevertheless it seems that some TVs with digital displays (ie fixed pixel) like the Sony LCDs do convert to analog anyways. Not a decision based on achieving optimal video quality, but most likely related to financial reasons.


Ed
 

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Discussion Starter · #11 ·
Quote:
Originally Posted by BillP
They may not require it, but it's apparently cheaper to make it that way, and Sony apparently cut corners.
Wow - talk about similar responses. I guess mine took a couple of seconds longer to type since it's 2 lines long :p


Ed
 

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Guys, I'm not arguing that Sony does it, I'm just noting it isn't technologically required.
 

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The question is now which display devices are not converting an HDMI signal to analog?


It's like a bobmshell dropping. And no-one is supposed to know about this?


I mean me and others try to help fellow forum members as much as possible, we keep telling them that HDMI is a better technology because of the fact that there is no conversion to analog while the so called experts on this forum stay quiet on the sidelines? In all the conversations about HDMI I have never seen any of those so called experts say anything about it.
 

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Quote:
Originally Posted by htpcfan
It's like a bobmshell dropping. And no-one is supposed to know about this?
I'm not sure what you are referring to. In DLP threads, where I spend most of my time, every new model gets the "does it have an all digital path from DVI/HDMI?" treatment. That's why I know about the sets I listed in my first message.


I've never been sure how important it is, but I did go with a set that has a digital path for it's DVI and HDMI ports.


Based on your screen name you must have an interest in HTPC inputs. I'm using one and get outstanding de-interlacing and scaling from it. I'm not sure it would be as good on a 2004 Mitsubishi DLP.
 

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Quote:
Originally Posted by rogo
LCDs do not require an analog stage.
Thanks for the information. I've corrected my "impression".
 

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Unless the display is a DLP, plasma, or eLCoS-type , involving pulse width modulation or other all-digital processing in the final display stage, analog signals for display elements are involved. (Would think similar all-digital processing could also be applied to some updated versions of other fixed-pixel displays, such as LCDs.) Here's one text-book-type reference to PWM and displays. Whether there's additional DVI/HDMI-to-analog processing before the last analog-fed display elements would depend on individual design as discussed earlier. -- John
 

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Quote:
Originally Posted by rogo
LCDs do not require an analog stage.


The only display tech that needs an analog stage is CRT.
Wrong. I think you are confusing fixed pixel pitch with analog drive.


All the LCD's used in Televisions (RPTV and large direct view) of which I am aware store an analog level to drive the pixel. They are driven by Analog signals that set the level of the pixel and digital circuits to select which pixel (or subpixel in the case of 3-color flat panels) .


Today, most of the processing, particularly scaling, is done digitally. But in an LCD display there will be at least one conversion to analog and the LCD column drivers are analog.


For example quoting from National Semiconductor's Web site on their chips to drive Flat Panel LCDs http://www.national.com/appinfo/fpd/ppds.html:
Quote:
Column driver

The column driver receives data via the PPDS interface and uses a linear DAC to convert the incoming data to the appropriate output voltage. The column driver also operates at a 2.5V digital supply. Because the column driver uses a linear DAC instead of the traditional non-linear R-DAC, the total number of reference voltages needed for the gamma curve has been reduced from 18 to 6. Overall, the PPDS interface significantly reduces (by up to 50%) the total number of column driver input signals needed.
 
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