Emerging 2K digital cinema and 3-D production are becoming more widespread, and existing infrastructure may not fully or transparently handle these advances in technology. The ability to inject a specific video format into the production chain and monitor it at each stage can ease the introduction of these new formats, as well as fault-find when things are not working correctly.
3G-SDI T&M equipment has to provide tools to allow engineers and equipment manufacturers to quickly check these emerging formats are supported. “Analog-type” displays (such as picture monitors, vectorscope and waveform monitors) give the engineer an instant view of the decoded data within the 3G-SDI feed to provide a level of confidence that the image data is correct. They decode and display the ancillary data within the 3G-SDI feed to allow the engineer to check its integrity and compatibility with other equipment.
For example, the audio for digital cinema is up to 16 channels of broadcast WAV or uncompressed 24-bit samples at 48kHz or 96kHz.
Stereoscopic television can also employ CIE XYZ color space, 2048 x 1080 pixels; however, it has a frame rate of 48fps (24fps for each eye).
The latest analyzers now support 2K XYZ color space formats and sample rates, as well as 2K digital cinema as defined in the SMPTE ST 2048-2:2011 standard (2048 x 1080 Digital Cinematography Production Image FS/709 Formatting for Serial Digital Interface). 2K test patterns allow “before-and-after” comparisons to be made as 2K material is processed and distributed. The standard test patterns used in HD-SDI test and measurements are now available in the 2K world to allow broadcast engineers to comfortably use their skills in the digital cinema world.
As with HD-SDI, the metadata is a vitally important part of the content of the 3G-SDI data stream and now contains even more complex information that defines the content, mapping and color space information for the material being distributed. An understanding of this metadata is critical to transparent processing (routing, switching, editing, insertion, etc) as well as a method of checking the actual metadata present in the data stream. CRC-based content checking, measured over long periods of time, ensures that no data errors are present in the transmission.
The testing of 3G-SDI, like all new innovations, takes time for the industry to get to grips with, and will be well-established standard practice just in time for the next round of innovation. The knowledge, skills and experience gained by the industry during the implementation of HD-SDI are directly applicable to 3G-SDI.
The parameters and tolerances defined in SMPTE 424M specification for 3G-SDI are even more critical than those defined in SMPTE 292M for HD-SDI. Therefore, testing of signal quality and compliance is paramount to ensuring correct and reliable functionality.
- Alignment Jitter refers to artifacts above the specified threshold frequency of 100kHz for HD-SDI signals. Typically video equipment will have difficulty tolerating Alignment Jitter > 0.3 UI which cause decoding errors due to incorrect sampling.
- Timing Jitter refers to a longer-term time-interval error above a low-frequency threshold of 10Hz. Large amounts of Timing Jitter can often be tolerated.
—Alan Wheable is senior technical author at Phabrix.