audio for video feature
However, can it honestly be said that year's Spring PlugFest, the Audio
the EDID is accurate if the 96kHz audio Precision team was able to observe
is received by the device, but is what was happening down at the
reproduced full of dropouts and pops, metadata level when some of the
as was the case with an HD television HDMI devices at the show were
Audio Precision’s engineers were connected together, thanks to a
testing recently? recently added feature in our APx
analyser that presents metadata in a
Why (and why does it view like a logic analyser. To take one
matter)? example we observed, when two
HDCP content-protected devices are
It's not clear what causes the hooked together, they have to decide
If written such that
mistakes in HDMI EDID, but it’s whether they're going to allow
it correctly
What's to be done?
possible to speculate, based on some digitally protected content to pass
describes its parent
of the errors that crop up regularly. from one to the other. They're
device, this
Preventing such scenarios is easy,
unfriendly looking
Some manufacturers seem to be supposed to have a short 'digital hex readout - the
although it requires support from the
uncertain how to write the required handshake', authenticate each other,
code at the heart
manufacturer for a proper
of the EDID - can
information in accordance with the and if successful, exchange encryption
make HDMI
programme of R&D and subsequent
EDID specification. Some appear to be keys and begin encrypted transfer. But equipment testing
audio and video testing for products
using off-the-shelf EDID information some of the hardware doing this was
and
under development. Use of off-the-
troubleshooting
produced by third parties which authenticating, starting encryption, de-
much easier.
shelf EDIDs should be avoided, and
doesn't correctly describe their authenticating, re-authenticating,
the product design team, who need
product. This might be due to starting again... the devices took a lot
to be trained properly in the art of
oversight; perhaps the companies longer to settle down and get on with
writing properly specified EDID
concerned have bought the third-party the transfer than they should have.
information, should create it such
EDID as a starting point to describe With consumer equipment pairings like
that it properly describes the
their product, but they never get HDMI-equipped Blu-ray players and
capabilities of the specific product -
around to adapting it for their device. TVs, authentication errors like this
and not just one in that range. The
Others may be producing EDID could lead to a noticeable delay of
device should then be given to an
information for a top-of-the-range several seconds between a consumer
EDID-conversant test engineer,
product, and then using that same pressing Play and playback beginning
ideally someone not involved with
data for all of the products in the on screen. That's the kind of thing
the product design, who should
range, without considering that the consumers would notice, and which
decompile the EDID. This is not as
EDID is inaccurate for the entry-level would compare unfavourably to old
hard as it sounds - plenty of
product in the same range. home video systems, even analogue
companies, Audio Precison included,
There's no doubt that producing an ones like VHS.
make devices capable of reading and
accurate HDMI EDID requires care, and Ideally, this kind of problem should
editing EDID.
that as the number of available be picked up at the R&D stage of the
But just reading the EDID isn’t
formats for HD video and audio product's development, rather than at
enough; the engineer also needs to
delivery has grown, the task has a PlugFest, before the scrutiny of the
test the device's ability to cope with
become more complex. It could be world's HDMI manufacturers. The very
the media formats the onboard EDID
that the situation will both improve fact that PlugFests are popular
says it can handle. Again, this isn't
and worsen over time: manufacturers suggests that manufacturers are
difficult: it's simply a matter of
may become more appreciative of the having problems with HDMI, and that
constructing a test programme which
importance of producing accurate EDID the tools they're using to check their
involves firing these media types -
information, and also more equipment aren't very good. There’s
But just
including obscure HD video and
accustomed to the task, as time goes sense in using PlugFests in addition to
reading the compressed audio formats where
by, but new formats will continue to a carefully designed in-house
EDID isn’t
necessary - at the device under test
develop, which means it won't be programme of rigorous product
enough; the
and evaluating the results. With
easy to stay on top of the situation. testing, but a few ad hoc
engineer
modern video and audio test
It's been interesting to watch the interconnection tests performed on
hardware, the process of testing,
growing popularity of the now-regular some pre-production hardware at a
also needs to
analysis and results reporting can be
PlugFest events organised by HDMI PlugFest shouldn’t be considered a
test the automated and integrated into a
manufacturers; this can be interpreted replacement for proper product device's
software-based process control
as a measure of just how difficult it testing programmes. None of this is
ability to
environment like LabView. In this
can be in this digital, metadata-driven likely to matter if a manufacturer of
cope with
way, any problems with the EDID or
age to create products that are broadcast technology produces
with the device's ability to behave
compatible with a wide range of devices that respond to well-
the media
according to its advertised
industry hardware. established standard audio and video
formats the
specification could be picked up long
For those unfamiliar with PlugFests, formats, and correctly flag this fact in
onboard before the product reaches end
they're essentially opportunities for their EDID. However, if the EDID
EDID says it
users. None of this need replace
manufacturers to meet and bring along incorrectly says the device will receive
can handle
testing sessions at the likes of
their hardware and software, (say) compressed formats, like Dolby's
PlugFest, but it might make for more
sometimes at an early stage in the AC-3, and this fact has not been
reliable HDMI equipment at both the
development of a new product, so that tested or brought up at a PlugFest, the
broadcast and consumer level, which
they can try connecting it to other first people to find out might be the
has got to be a good thing for all of
manufacturers' equipment. At this manufacturer's customers.
us.
www.ibeweb.com l may/june 2009 l ibe l 29
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