Does the BD player affect HDMI output quality?

[hjb981]

I think that I am in need of an explanation.

When I read reviews of blu-ray disc (BD) players, they usually include comments on both the audio and video quality. My question is, how can there be any difference between different players? The BD is decoded to an HDMI signal by the BD player. Is this process not deterministic, i.e., the output is always the same?

Many other compressed formats, such as jpeg for pictures or mpeg for movies, work in this way. A jpeg file will produce the exact same RGB values for each pixel no matter on what computer it is decoded. In other words, if two different computers were used to show the same jpeg picture on the same screen (connected by a digital connection such as display port, DVI or HDMI), the picture should look exactly the same, independently of the computer used.

Are the quality differences only present when using the analogue outputs of the BD player? Is there any filtering, noise reduction or other processing going on that would affect also the digital HDMI signal? If so, can such things usually be turned off?

edit: I can understand that the quality differs if the player has to change things, like for example converting a 24p (24 frames per second) recording on a BD to 30p. My question is more related to the case where this is not done, i.e., the same frame rate as the BD is recorded in is also output over HDMI.

To sum it up: it seems very reasonalbe to me that if a digital data stream (the contents of the BD) is read and decoded into another digital data stream (the HDMI signal), one should get the exact same result with any BD player. If I am wrong, I would greatly appreciate it if anyone could explain to me how there could be a difference.

 

[j_garcia]

A big part of your assumption is incorrect, since there is a video DAC that decodes the video and the quality of that DAC determines the quality of the video regardless of what output type is used. HDMI itself is not a factor for the reasons you've given. That said, even inexpensive players these days are capable of excellent quality, so the end result today would seem to be that I wouldn't expect a massive difference in video from a top dollar player like we used to see with DVD players.

FYI, analog video is dead on home players. Take a look at most current TVs, players and even receivers. Very few have analog connections anymore, aside from supporting legacy gear.

 

[hjb981]

Thanks for the reply. DAC stands for Digital to Analogue Converter, but the HDMI transfers digital signals. It is not possible to first convert from digital to analogue, and then send it over HDMI (unless the analogue signal was converted back to digital again with an ADC (Analogue to Digital Converter), but it would seem very strange to first convert from digital to analogue and then back again). For the most common setup today, where HDMI carries a digital signal all the way to the TV, the DA conversion is made by the TV (which hence should have a DAC in it that has an effect on the picture quality). Did you perhaps refer to something else than a digital to analogue converter when you used the abreviation DAC?

 

[Pyrrho]

I think that I am in need of an explanation.

When I read reviews of blu-ray disc (BD) players, they usually include comments on both the audio and video quality. My question is, how can there be any difference between different players? The BD is decoded to an HDMI signal by the BD player. Is this process not deterministic, i.e., the output is always the same?

Many other compressed formats, such as jpeg for pictures or mpeg for movies, work in this way. A jpeg file will produce the exact same RGB values for each pixel no matter on what computer it is decoded. In other words, if two different computers were used to show the same jpeg picture on the same screen (connected by a digital connection such as display port, DVI or HDMI), the picture should look exactly the same, independently of the computer used.

Are the quality differences only present when using the analogue outputs of the BD player? Is there any filtering, noise reduction or other processing going on that would affect also the digital HDMI signal? If so, can such things usually be turned off?

edit: I can understand that the quality differs if the player has to change things, like for example converting a 24p (24 frames per second) recording on a BD to 30p. My question is more related to the case where this is not done, i.e., the same frame rate as the BD is recorded in is also output over HDMI.

To sum it up: it seems very reasonalbe to me that if a digital data stream (the contents of the BD) is read and decoded into another digital data stream (the HDMI signal), one should get the exact same result with any BD player. If I am wrong, I would greatly appreciate it if anyone could explain to me how there could be a difference.

Of course you are right in your later post that the player is not using any DAC for sending the signal to the receiver (or TV) via HDMI, as that is pure digital. But some players process the signals in some way, and virtually all do in the case of the video for DVDs that are played on a BD player. With BD, in most cases, it should look and sound the same, as long as they are able to properly read the discs (some may be better than others at error correction, so there can still be differences). There are exceptions, as, for example, the new Oppo BDP-103D if the "Darbee" processing is engaged; it adds to the signal, which you may or may not like, but it can be switched off (though then there is no point in having it instead of the less expensive BDP-103). But since most BD players upconvert DVDs to output them via HDMI, they will look different, and which will be better will depend on the quality of the upconversion built into the player.

As for written reviews of audio and video products, there is nothing stopping idiots from writing reviews, and so some of them can be quite idiotic. Some "differences" can be explained by the placebo effect. This sort of thing applies to more than just audio and video gear; research has shown that when people believe that a wine costs more, then tend to think it tastes better than when they are given the same wine and told it is inexpensive.

To sum up: As long as the players can properly read the disc, and all processing is off, then the HDMI output should be identical in all cases. This does NOT mean that all are equally good, as some are more reliable than others, and some can play types of discs that others cannot (e.g., SACD, DVD-Audio, PAL video, other regions of DVDs and/or BDs, etc.). And, of course, the upconversion that they almost all do for DVDs will differ, and so one's DVDs may look different on different players.

 

[j_garcia]

Yes, DAC was the wrong term, but the player DOES process the signal and uses its own internal functions to do this prior to sending it to the display. Even though that signal is all digital, there's processing going on based on chips and firmware in the device that ultimately giving you your picture quality. AFAIK, other than the available options in picture adjustment, there's no way for a user to disable this.