HDMI - Video/Audio DACs

mattjax05

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Just a quickie!

Presumably when you send the audio/video signals from a blu ray player to an amp (then to the tv) via HDMI the D/A conversion takes place in the Amp for sound and TV for video?

If this is true, when player's audio/video are judged are they done on this basis i.e not relying on the player's internal DACs?
 

mattjax05

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Thanks Nads, hopefully we can get an answer this time round.

I recently purchased the Pioneer BDP51FD which came with a solid audio and video review however am I actually using the player's abilities because of the HDMI connection? I'm not quite sure what other procedures the player needs to carry out if you are not decoding the sound there or using its DACs?
 

Tom Moreno

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Hi guys,

The HDMI cable caries audio in digital form, not in analogue. As such if you send the audio to an AVR via the HDMI connection you would be bypassing the player's DAC completely and performing the D/A conversion in the receiver itself (after the receiver's processing stages performing various delay functions, crossovering, EQing, and possible phase correlation) right before sending the audio to the amplifiers. From a technical standpoint, if you send original bitstreams out the HDMI the player should be acting solely as a transport and not really have an influence on audio. In real world terms there are certain aspects where different players can influence audio quality even under these circumstances, but these tend to be by smaller margins and relate more to control over digital jitter and the quality of the internal clock. When you convert your Dolby TrueHD and DTS-HD MA to PCM inside the player either for an AVR that cannot decode these formats internally or to take advantage of Secondary audio mixing features and BD-Live the player has a much greater influence on audio quality, closer but not as severe as the traditional differences offered between varying qualities of DAC.
 

mattjax05

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Tom Moreno:

Hi guys,

The HDMI cable caries audio in digital form, not in analogue. As such if you send the audio to an AVR via the HDMI connection you would be bypassing the player's DAC completely and performing the D/A conversion in the receiver itself (after the receiver's processing stages performing various delay functions, crossovering, EQing, and possible phase correlation) right before sending the audio to the amplifiers. From a technical standpoint, if you send original bitstreams out the HDMI the player should be acting solely as a transport and not really have an influence on audio. In real world terms there are certain aspects where different players can influence audio quality even under these circumstances, but these tend to be by smaller margins and relate more to control over digital jitter and the quality of the internal clock. When you convert your Dolby TrueHD and DTS-HD MA to PCM inside the player either for an AVR that cannot decode these formats internally or to take advantage of Secondary audio mixing features and BD-Live the player has a much greater influence on audio quality, closer but not as severe as the traditional differences offered between varying qualities of DAC.

Hi Tom

Sounds to me as quite a big disadvantage for the HDMI connection - if you have the best DACs in the world in your player the only way to get them active is to use component for video and the multi channel analogue outs for sound (a lot of cables!)

So when WHFS&V review these players and report their findings (which have a lot of influence on buyers) what is actually getting reviewed?
 

mattjax05

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Could I please get some clarification on this. I'm particularly concerned about what connections are made between equipment when the revew team look at blu ray players?
 

nads

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TBH i dont think we will.

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mattjax05

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I did say please - what if I said pretty please?
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I'm tempted to buy some cables to hear/see the difference in A/V quality - I'm confident that there will be! What do you think?
 
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Anonymous

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Hi guys,

You can use HDMI purely to carry your picture signal and make use of the onboard decoding of your blu ray by connecting it to your amp with analogue cables (provided your blu ray has analogue outputs for this purpose).

Currently I am using a PS3 as blu ray source and this is connected direct to my display by HDMI with an optical cable carrying the audio bitstream (but not the high definition audio available on blu ray) to my pre-amp./processor a Naim AV2.

The original question asked was a good one and still hasn't been answered and that is when reviews are describing the sound of a blu ray player are they describing the sound of the bytes delivered to the receiver and decoded there or the sound of the onboard decoding?

This is an important question for me because I am not letting go of the Naim AV2 for love nor money and it cannot decode the high def. audio from blu ray, hence I need a machine with top notch onboard decoding (and decoding of all the high def. audio formats for that matter). A recent blu ray comparison had the Sony 5000ES awarded top honours based on it's sound over the Pioneer LX9, although the LX91 had a slightly better "picture".

So what is the answer Tom, when the sound of a blu ray is described in a review is it the sound of the onboard decoding or the bitstream delivered to the amp?
 

nads

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Still nothing from the team!

the more i read into it i came to the conclusion that there is no need for expensive BD players if you are using HDMI as all they are are transports.

Have good DACs in the amp and good processing it the TV.

emotion-14.gif
 

professorhat

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There's definitely more to it than that. I can't explain what, but look at the Denon DVD-2500BT. It doesn't have any analogue outputs and costs £700 - £800. Therefore, if it was exactly the same as a £150 Sony Blu-Ray player outputting via HDMI, it couldn't have got 5 stars.
 

Clare Newsome

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professorhat:
There's definitely more to it than that. I can't explain what, but look at the Denon DVD-2500BT. It doesn't have any analogue outputs and costs £700 - £800. Therefore, if it was exactly the same as a £150 Sony Blu-Ray player outputting via HDMI, it couldn't have got 5 stars.

Precisely. The Denon, for example, uses a mechanism designed to read discs as stably and accurately as possible - less vibration; more AV information.

Why not go and listen to some Blu-ray players, using both output options (where available)? It's just what we do when we test.

There's more on this recent thread.
 

Tom Moreno

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Hi Guys,

I lost track of this thread after my previous comments. I'm sure that when the What HIFI team review these units they must test them under both sets of conditions. It would be interesting when reviewing BD decks if the WHF team could make a comment as to the relevant characteristics of audio performance under both HDMI connection and via analogue connection as more and more people will probably be bypassing a unit's DACs altogether and I must admit to being left a bit confused from one review to the next what exactly the description of the audio performance is based on. Even if you use HDMI and bypass the DACs you will still hear a difference between one player and the next for the exact reasons that Clare has mentioned. Yes Bits is Bits, but the shear data throughput of the bits being sent to make this happen is massive and data loss/correction is a very real part of the equation. The quality of better transports is mainly in their ability to send a much higher percentage of correct original bits as per the disc as possible and the construction techniques to achieve this are what distinguishes budget players from premium players. There are budget players that bat above their weight and some premium players that may not perform to their asking price so ultimately you should give the different options a spin and see what's the most enjoyable unit in your price range.
 
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Anonymous

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"It would be interesting when reviewing BD decks if the WHF team could make a comment as to the relevant characteristics of audio performance under both HDMI connection and via analogue connection as more and more people will probably be bypassing a unit's DACs altogether and I must admit to being left a bit confused from one review to the next what exactly the description of the audio performance is based on."

I totally agree with you Tom.
But then, based on that (BDP's DAC versus Bitstream)what's even more important is to suggest the right combination, i.e. the perfect match between a receiver and a player taking into consideration the merits of their respective DAC, analog stage, etc.

To be honest, I believe it is exactly what WHF does already, but being sometimes a bit more explicit could add a lot more value to us, your faithful readers.
 

mattjax05

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Clare Newsome:

Why not go and listen to some Blu-ray players, using both output options (where available)? It's just what we do when we test.

Please could you advise whether it is worthwhile testing my current player (Pioneer BDP51FD) with analogue outs for video and audio (I would have to buy the cables). The player is connected to a Yamaha DSPAX763 and then to a Samsung LE40M87BDX all via HDMI currently. I presume currently it's the Yamaha's DAC in action for sound and the Samsung's DAC for video.

Thank you.
 

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