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feature audio for video
Dr Thomas Kite, vice-president of engineering
Feature sponsored at audio analyser manufacturer Audio Precision,
by Dolby
explains the problem of incorrect EDID in HDMI
devices, looks at the risks inherent in an ad hoc
approach to testing EDID with a selection of
random HDMI sources and sinks, and advocates
a more systematic approach to HDMI test.
Towards better
EDID & HDMI testing
A
s the popularity of the that doesn’t accurately describe the video with a vertical resolution of
HDMI interface for HD device’s capabilities. This is frustrating, 1080 progressively updated lines.
video and audio grows in like having a beautifully laid-out spec Sometimes all the label does is
the world of consumer sheet that is riddled with inaccuracies indicate that the device can receive
and professional AV and incomplete information. Where’s incoming video in the 1080p format,
devices, and the number the sense in directing everybody to which it then decimates before
of available video and audio delivery the EDID, the handy one-stop shop for displaying it at a lower resolution.
formats using that interface increases, information about the HDMI There are similar ambiguities with
the pressure on manufacturers to
Dr Thomas Kite,
capabilities of that device, if the shop EDID information, as EDID is concerned
ensure the accuracy of their devices’
vice-president of
is full of information that is only with describing the formats that a
EDID (Extended Display Identification
engineering at
Audio Precision.
incomplete, or worse, incorrect? device can successfully recognise and
Data) is mounting. Generally speaking, the specification receive, and contains no information
Like HDMI itself - hey, let's have one of HD AV equipment is not always as about how a particular format will be
delivery format for video and audio clearly expressed as it could be, reproduced. If the EDID says a device
that can deliver anything up to HD especially in the consumer domain, will accept audio at a sample rate of
quality through one connector - EDID is where labelling is everything. In the 96kHz, and it plays the audio back
a simple, powerful idea, analogous to USA and Europe, for example, if you correctly, the EDID is accurate, even if
the spec sheet of the device in buy a TV that says '1080p' in large the device actually achieves playback
electronic form. Contained in one
To discover
letters on the box, it's not always a by sample-rate converting the audio
simple ROM, and in typically just a what formats guarantee that the screen can show down to 48kHz internally beforehand.
couple of hundred bytes of data, is all
a piece of
of the information about the video and
hardware can
audio formats the device can receive
and do business with. In the world of
cope with
broadcast manufacturing and test, it's
over HDMI,
a welcome innovation, because if you all you have
want to know what formats a certain
to do is read
piece of hardware can cope with over
its EDID. At
HDMI, all you have to do is read its
least... that's
EDID. At least... that's the theory.
the theory
Theory vs Practice
In practice, there seems to be quite
a lot of equipment out there with EDID
28 l ibe l may/june 2009 l www.ibeweb.com
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