HDMI audio devices need rigorous tests
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 4/1/2009 2:00:00 AM
When you connect a DVD or Blu-ray player to an HDTV, you expect the player to send the highest quality video and audio that the TV can support. That doesn't always happen, even though HDMI (high-definition multimedia interface) equipment manufacturers attend “plugfests” before shipping their products to market. Plugfests offer an efficient way for manufacturers to test their products, but they can't guarantee that every DVD or Blu-ray player has been tested with every TV.
| To learn more about how Kite and Mathew conducted these tests, read their full interview with Martin Rowe: "HDMI audio needs plugfests and standard tests". |
Tom Kite, VP of engineering at Audio Precision, attended a plugfest in October 2008 and found that not all HDMI products deliver the audio formats that they claim to support. An HDMI sink such as an HDTV contains a ROM that holds information about the audio and video formats that the TV supports. An HDMI source such as a Blu-ray player is responsible for reading the sink's EDID (extended display identification data) from the ROM and providing the highest quality formats that both devices can support. Sometimes, though, a sink's EDID contains information indicating that the sink can support formats that it really can't. That's where interoperability problems can occur.
At the plugfest, an engineer approached Kite about testing his SPDIF (Sony/Philips Digital Interconnect Format)-to-HDMI audio converter, which is both an HDMI source and sink. Upon analyzing the SPDIF input audio and the HDMI output audio, Kite discovered that the converter had truncated the last four bits of audio in a 24-bit stream. “The engineer couldn't believe it,” said Kite. “He was ready to release the product and now had to fix the problem.”
Audio Precision engineer Dave Mathew found issues with Blu-ray players. For example, one player that supported movies with LFE (low-frequency effects) in its audio was clipping the output signal. Apparently, not all players put out the same digital audio at the same amplitude levels.
To learn more about how Kite and Mathew conducted these tests, see "HDMI audio needs plugfests and standard tests". There, you will learn why losing four of 24 bits of audio can cause a TV to reject an incoming audio stream.
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