Audio Precision has announced several new features for its APx Series of audio analyzers. These features relate to the display, analysis, and control of metadata in HDMI (high-definition-multimedia interface); IEC (International Electrotechnical Commission) 60598 standard, which defines the Toslink and S/PDIF (Sony/Philips digital-interface format) consumer digital-audio interfaces; and AES3/EBU (Audio Engineering Society 3/European Broadcast Union) digital-audio streams. The additional features are available in the first beta release of APx500 Version 2.4 software. The vendor expects to release the full Version 2.4 this year. “Errors in metadata can cause real problems in HDMI that you just don't see in S/PDIF,” explains Dan Knighten, Audio Precision’s director of products. “A logic-analyzer view shows exactly what’s going on over time so you can identify what’s causing glitches or other issues.”
Three features of the new release, including two new metadata monitors, relate to the analysis and management of metadata. One of these monitors allows decoding and displaying the entire HDMI audio InfoFrame, including the current values of CTS (cycle-time stamp) and N, a constant that CTS uses to define the relationship between the audio-sample clock and an HDMI link’s TMDS (transmission-minimized-differential-signaling)-master-clock values, HDCP (high-bandwidth digital-content-protection) state, audio layout, and audio/video-mute condition. The second monitor displays information about the channel status and user bits embedded in IEC60958/AES3/EBU-format audio content. Both the HDMI and the IEC60598 audio monitors also display the digital-audio stream type and sample rate, as well as Dolby and DTS (Digital Theatre Sound) parameters, including the dialogue-normalization level, bit rate, and ACmod/Amode values. ACmod for Dolby and Amode for DTS are metadata that define a bit stream’s number of encoded channels.
Two new metadata-editor panels allow you to override default metadata settings and set channel-status information and HDMI audio-InfoFrame data to any value. You can use these panels to verify the response of a device under test to both valid and invalid settings. The metadata recorder is an easy-to-read color display, which, in a logic-analyzer-like display, can plot the changing states of multiple metadata fields in real time. You can simultaneously display as many as 15 fields, so you can monitor in detail what happens to metadata when you hot-plug an HDMI device, or you can determine when and where data glitches occur in a corrupted audio stream. The system also automatically identifies and flags discrepancies between the indicated metadata and the received metadata—for example, if the input sample rate is 48 kHz but the channel status indicates that it should be 44.1 kHz. The results of such measurements are helpful in verifying that a device under test’s behavior complies with relevant specifications.
Audio Precision
