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Discussion Starter · #1 ·
Here is what I read recently in "The Perfect Vision", issue 74 (Jan 2007):


"according to a contact in the HDMI licensing organization, who spoke with me on condition of anonymity about some of the problems he encounters testing manufacturer's prototypes and production units. Unlike free-streaming analog video, to begin transmission, HDMI requires two-way handshaking between source and display, or three-way handshaking between source, A/V receiver, and display, during which the devices identify themselves and their capabilities. This determines what users will experience: stereo vs. surround sound, for example, or 1080i vs. 1080p. HDMI defaults to the lowest common denominator in the network, which was our AVguide poster's problem: during handshaking, the source determined that the TV was stereo-only and locked all audio to stereo output."


As I understand, according to this, if I have DVD player -> A/V receiver -> TV, all connected using HDMI, I will never get audio better than stereo.


What's wrong with my understanding?
 

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I suspect that the correct interpretation is that the TV's audio defaults to the lowest common denominator. The receiver does not have to alter the audio for it's internal use to the lowest common denominator.


I am guessing here, but I think what this all means is that the receiver is responsible for sending usable audio data to the TV, perhaps 2-channel PCM.
 

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Actually, devices should in most cases automatically configure themselves to transmit the highest common audio & video denominators, not the minimum. However, it's not required by HDMI that devices automatically self-configure themselves to the highest denominator- it's ultimately a manufacturer's design to do this (though there are no technical reasons why they can't make it automatically go to the highest). HDMI requires, at minimum, that all devices be able to support 480p video and 2ch PCM stereo audio. I have seen one manufacturer design their device to be factory set to output only 480p and 2ch PCM on the HDMI output only, and the user is required to go into its configuration menu to manually select the option to transmit higher quality audio format (such as DD & DTS) and 720p video. The only reason I can imagine why a product would do this is out of fear that another device has poorly written EDID which could cause their playback device to send the wrong audio/video format, resulting in a blank screen or no sound. By making 480p and 2ch stereo the default, users are pretty much assured to get compatible audio & video so that they can bring up menu's and navigate to the setup menu.


For the case of stereo only being sent to a TV, if a DVD player (for example) is connected directly to a TV with HDMI and the TV can only support the decode of 2ch PCM audio, then that is what the DVD player will send it, and it should because the TV specifically is reporting that it won't handle any other audio format. In the case of a DVD player-> AV receiver -> Stereo only HDTV, the DVD player will normally not be limited to stereo only on HDMI because the AV receiver acts as a repeater. HDMI AV receiver will typically have its own EDID chip and report the ability to support multiple audio capabilities such as 2ch PCM, 6ch PCM, DD, and DTS. So the DVD player should send the highest quality audio format mutually support by itself and the AVR over HDMI to the AV receiver, which then extracts the audio stream and presents it through its speaker system. The AV receiver then talks to the HDTV, and sees that the TV can only handle 2ch stereo. Most HDMI AV receiver would then 1) downsample the audio stream to 2ch stereo and send it to the TV over HDMI, 2) mute the audio and send video only to the TV, assuming the consumer want the receiver to render the audio and the TV to be a display only, or 3) offer the user to select #1 or #2. Most HDMI AV receiver are their own sink/source because this is how consumer expect to use them.


Even in the worst case where the device defaults to lowest common denominator, users should still have to option to manually force the device to a higher quality audio/video format (so long as it is mutually supported by all the connected devices).
 

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Discussion Starter · #5 ·
HDMI_Org,

I tend to agree that GCD (greatest common divisor) would be more appropriate, but I believe that the key word here is "common".

Interpretation of AVGuide's source is that it's required that all devices fall back to common supported standard. However, your interpretation that it's not required ("it's not required by HDMI that devices automatically self-configure themselves to the highest denominator").

Clearly, we have a disagreement within HDMI how to read own requirements.

I searched your website for clarification. But you want $15000.00 just to be able to get access to requirements. HDMI describes differences between versions, but no 1.0 itself.

Could you provide some independent source which corroborates your interpretation, or any interpretation for that matter?

Thank you.
 

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I'm afraid I don't understand your requests or assertion that our interpretation of the specification is not consistent. Could you elaborate? Feel free to send me a PM as well.


Note the HDMI Specification is free for anyone to download through the HDMI website, though there is a click through where we take your contact info.
 

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Discussion Starter · #7 ·
Well, I downloaded 1.3a spec without paying a penny. I'm still not sure it's legal, because taking my contact info you require company name and I don't have one. I put instead "myself" and it was accepted.

Funny enough word "repeater" is not mentioned even once out of 276 pages. So, as far as HDMI is concerned there is no such thing as repeater.

Specs talk a lot about source/sink pairs. And they all need to be synchronized in term of supported features before any communication starts.

What happens after that is still murky for me.
 

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One more clarification, which I re-iterated on this thread:
http://www.avsforum.com/avs-vb/showt...73#post9631373


In summary, when using a device in the chain that has the ability to perform processing & alteration of the audio & video streams (such as an AV receiver), such a device will decouple the capabilities of devices upstream and downstream of it. So in a typical home theater setup:

DVD player -> AV Receiver -> HDTV

The DVD player will send the highest quality formats the AV receiver can handle (and does not care what the TV can or can not do, because the AV receiver does not present those limitations to the DVD players). Then the AV receiver processes the audio & video (can be passthrough, upconversion, or downconversion) and sends it as the highest quality that the TV says it can handle.


I'm looking at the HDMI 1.3a spec, and there are 49 instances of the word "repeater" mentioned. The first instance is on page iv, 2nd line from the top. Perhaps your version of Acrobat Reader does not have a search function.
 

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Discussion Starter · #10 ·

Quote:
Originally Posted by HDMI_Org /forum/post/0


I'm looking at the HDMI 1.3a spec, and there are 49 instances of the word "repeater" mentioned. The first instance is on page iv, 2nd line from the top. Perhaps your version of Acrobat Reader does not have a search function.

I stand corrected: while searching for "repeater" I had case-sensitive checkbox selected and didn't notice that, but "repeater" in the document has every R capitalized. I apologize.
 

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Discussion Starter · #11 ·

Quote:
Originally Posted by HDMI_Org /forum/post/0


In the case of a DVD player-> AV receiver -> Stereo only HDTV, the DVD player will normally not be limited to stereo only on HDMI because the AV receiver acts as a repeater. HDMI AV receiver will typically have its own EDID chip and report the ability to support multiple audio capabilities such as 2ch PCM, 6ch PCM, DD, and DTS. So the DVD player should send the highest quality audio format mutually support by itself and the AVR over HDMI to the AV receiver, which then extracts the audio stream and presents it through its speaker system. The AV receiver then talks to the HDTV, and sees that the TV can only handle 2ch stereo. Most HDMI AV receiver would then 1) downsample the audio stream to 2ch stereo and send it to the TV over HDMI, 2) mute the audio and send video only to the TV, assuming the consumer want the receiver to render the audio and the TV to be a display only, or 3) offer the user to select #1 or #2. Most HDMI AV receiver are their own sink/source because this is how consumer expect to use them.


Even in the worst case where the device defaults to lowest common denominator, users should still have to option to manually force the device to a higher quality audio/video format (so long as it is mutually supported by all the connected devices).

From what I've been able to gather so far the relevant information is on p.134, Appendix A Repeater. I have not found or been able to induce a requirement mentioned in TPV's article, but what I found no less disturbing.


1. The E-EDID presented by a Repeater should reflect the capabilities of the downstream Sink.



2. In terms of E-EDID handling, Repeaters will typically fall into one of the following categories.


- Stored E-EDID type: The Repeater stores an E-EDID data structure that typically consists of

downstream Sink capabilities.


- Forwarding type: The Repeater does not store an E-EDID data structure. When an E-EDID

read request comes from a Source, the Repeater forwards the read request to a Sink. The EEDID

data from the Sink is then forwarded back to the Source.


Here we have forwarding type, which would lock source to stereo only. But even in stored E-EDID type repeater behaves the same way in typical case. So, typically ( = typically out of typically + some non-typical), in a cluster source->repeater->display source will be locked to minimum capabilities out of source's own and display's.


And, as far as consumer is concerned there is no way to find out an actual behavior of A/V receiver beforehand. In a typical HDMI fashion this behavior is optional, and because it's not on the same level as Deep Color, it's not going to be advertised by manufacturers.


The following excerpt has nothing to do with issue in question, it's just an example how standard written:


In all cases, each HDMI input shall fulfill all of the requirements of an HDMI Sink when it is

connected with an active sink device, and each HDMI output shall fulfill all of the requirements of

an HDMI Source when it is connected with an active source. (bold is mine)


How is it input connected with sink and output with source? No wonder all of the confusions among manufacturers and consumers.
 
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