[Tomas L]

You can read everywhere about the latest 14 bit/108MHz DACs, but is the difference really noticeable? Have anyone compared? Are they so much better than the "old" 54MHz DACs? What's the difference and do you need a 10' image to see it?


Maybe I should wait for the next generation 16 bit/216MHz DACs...?


(questions, questions, questions...)

 

[Tomas L]

..........?

 

[spkrgeek]

Tomas,


I compared the 12bit/108Mhz progressive output to the 10bit/54Mhz interlaced output in my Denon 3800 using the color spectum ramps on the AVIA DVD. The 12 bit progressive output was noticably better. The color transitions on the test signal seemed smoother and there was less "banding" of the colors. I guess I would attribute this to the higher bit depth (i.e. 12 bits, vs. 10 vs. 8).


To be fair this is not an apples to apples comparision of the video D/A sections, as alot of extra stuff is inserted into the path on the progressive output. I have not really noticed any real color inprovement on ordinary video material that I would attribute directly to the video DACs.


I'm not really sure what the oversampling (i.e. 108 Mhz vs. 54 vs. 27) buys you in a video DAC. In audio DACs oversampling is used to avoid aliasing and allow for a more gentle low pass filter. I'm not sure what the video equivalent would be.


Chris

 

[pnichols]

spkrgeek,


I believe the principles are the same between what can be gained in audio with higher oversampling vesus higher video oversampling. Someone can correct me if I'm wrong, here.


The high bandwidth video DAC's can be used to move aliasing noise further up in, or out of, the video pass-band so less steep low pass video filters can be used.


I suspect that it's only recently with the availability of the very close dimension spacings in CMOS silicon wafer processing, that companies like ADI and others have been able to inexpensively offer the necessary speeds and bit depths in video DAC's to do this video DAC aliasing noise spectrum shifting. I know that in the company I'm in, 14 bit video DAC's at speeds above 100MHz get REAL challenging.

 

[Tomas L]

Thanx!

 

[kjack]

Quote:

Originally posted by pnichols spkrgeek, I know that in the company I'm in, 14 bit video DAC's at speeds above 100MHz get REAL challenging.

The problem is just saying "n bits / x MHz" is pretty meaningless. A 12-bit DAC with good linearity will perform better than a 14-bit DAC with poor linearity. Then there's switching noise, power supply noise, settling time, etc. that also affect DAC performance and video quality.


Higher samples rate do help simplify the DAC filters and keep the passband flatter. However, if the TV digitizes the video inputs for digital processing, then all that effort could be largely wasted...but it will look good on the test equipment.


Then there's HDTV analog signals begging for even higher sample rates...