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Let's Be 'Clear' About HDMI

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avenuedubac's picture
Joined: 10 Aug 2007
Posts: 10

Joking aside, there is a lot of hyperbole about HDMI and a lot of misinformation even from the consumer press.  Reading back over previous editions of What Hifi etc, it is astonishing how naive some observers have been about HDMI.  Every reviewer who praises the number of HDMI inputs etc should note that HDMI is a data cable.  We all use data cables in our offices and perhaps in our homes, those little square jacks with multiple pins. The difference between these computer cables and HDMI is that computers have intelligence built in at each side of the 'connection' called protocols (OSI network protocols) that do a very good job at buffering and resending data packets. HDMI has none of this, a lost packet is a lost packet as they say, and there is no way of getting it back since the link between the player and the screen or projector operates in real time. Given this inherent weakness, any data cable over a certain length loses data due to RFI, and non linearities in the path (think of a 15m HDMI cable snaking its way to your projector in the ceiling).  This loss is not so bad at SD but ask the cable to transmit to a ceiling mounted projector at 720p and you are asking for considerable data loss (which defeats the whole point of HD), at 1080 it is not worth watching.  This happens to many so called expensive cables, even those armoured to the teeth.  Why, because the basic HDMI construction is flawed, as it is an unbalanced, basic set of twisted pairs. This comes of a bit of a shock when you pay upwards of 250 UK pounds for a cable that will need a repeater (current asking prices in the UK of 100 pounds or more) to get rid of those 'sparkles'.  Please, before you read the wrapper on the cable or the What HiFi glorification of HDMI, spare a thought about the basic flawed approach and think why we have telecommunications protocols to resolve data loss.  This advice comes from both an understanding of data communication and real life experience with 15m cables at 720p and above.  One saving grace, though, the repeater I bought (buy form Amazon in the US if you can) does what it says on the tin, but why have to pay for something to correct a basic flaw in the first place?

Andrew Everard's picture
Joined: 30 May 2007
Posts: 29118
Re: Let's Be 'Clear' About HDMI

 Kind of what I was covering here.


Audio Editor, Gramophone