Video Asylum TVs, VCRs, DVD players, Home Theater systems and more.

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ Video Asylum ]

---

[ Alert Moderator ] [ Edit ] [ Delete ]

---

Re: Any 12-bit / 108MHz DVD Players ?

66.87.138.121

Posted by Charles Hansen on May 2, 2002 at 08:45:43

In Reply to: Re: Any 12-bit / 108MHz DVD Players ? posted by Homer on April 30, 2002 at 22:02:07:

Hello -

Basically, the need for higher resolution DACs comes about because the DACs are not perfect. A 10-bit DAC is required to get even close to realizing the full 8 bits of resolution encoded on the disc.

Please allow me to explain further. As noted, DVD is an 8-bit format. However, the sync pulses are stored as special codes within the data stream. The DAC must convert these coded sync pulses into an analog output signal. This requires approximately 1 additional bit of range on top of the 8 bits required for the video signal itself. The very earliest DVD players all used 9-bit DACs for this reason.

(As an aside, some DACs have separate internal current sources used to generate the sync pulse. These effectively add an additional bit of true resolution. An example of this is the Analog Devices ADV-7122 used in the i-Scan. This is nominally a 10-bit part, but will match the resolution of an 11-bit part that doesn't have these separate current sources.)

However the problem is that no DAC is perfect, as they all exhibit non-linearities to some degree. A really good 10-bit DAC will be linear to +/- 1 least-significant bit (LSB), which is equal to 0.5 of the second LSB (or 9th bit). Since we need 9 bits just to recreate the video signal plus the sync pulse, this means that a really good 10-bit DAC will have an error of a half a bit on the video data itself.

We have now effectively turned a barely adequate 8 bit standard into a 7.5 bit playback system. Most 10-bit DACs used in cheap DVD players will have linearity errors greater than +/- 1 LSB, compounding the problem.

While the non-linearity of a higher resolution DAC will often be greater in terms of LSBs, these LSBs are much smaller than those of a 10-bit DAC. For instance, the 14-bit DACs used in the Ayre D-1 are specified to +/- 3 LSBs for integral non-linearity, and +/- 2 LSBs for differential non-linearity. (Integral non-linearity refers to the maximum error over the entire range of the DAC's output. Differential non-linearity refers to the maximum error from any one output level to an adjacent output level.)

This translates to an error of less than 0.1 LSB at the 8-bit level found on the disc itself. So now we are able to achieve 7.9+ bits of resolution in the total playback system, which is a noticeable improvement over the example noted above using high-quality 10-bit DACs (let alone average quality 10-bit DACs).

When processing straight video, there is an area of diminishing returns when going past 12 bits. We went to 14 bits in the D-1 as an example of what could be achieved with cost no object. (Please note that our ground-breaking design paved the way for the higher resolution parts that are now coming out in the mass-market players of today. The Analog Devices video group has consulted us on what features should be included in their product lineup, and they are now clearly leading the field in video conversion.)

However if there is any video processing going on (brightness, contrast, gamma, et cetera), then additional resolution is required in the DACs to avoid a loss of resolution in the final output signal. In this case, a 14-bit DAC would be required to achieve the resolution of a 12-bit DAC in a system without video processing. That is one reason why we don't offer any such adjustments in the Ayre D-1. Higher performance can be achieved by making these adjustments in the analog domain in the monitor itself.

Hope this helps,
Charles Hansen

This post is made possible by the generous support of people like you and our sponsors:

Parts Connexion

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---