ON TIME AND IN SYNC: THE LEADER LT4670 SDI/IP SPG AND TEST SIGNAL GENERATOR by Steve Holmes*

Timing became an integral element of visual media communication with the introduction of cinematography at the trailing edge of the 19th century, initially to ensure that the film was reproduced at the original frame rate – a subjective process during the early years of hand-cranked cine cameras.

The development of television in the early 1900s added the need for precise synchronization throughout the image scanning process. Sync pulse generators function as the beating heart of every TV content production and transmission facility even in today’s SDI/IP world.

Leader’s LT4670 combines the dual roles of sync pulse and test signal generation. Housed in a compact 1U x 400 mm chassis, it is designed for use in live broadcasting, film and TV production studios, OB vehicles, remote production coordination centers and post-production suites. It can also be used as a reference signal generator by TV equipment manufacturers, system integrators and maintenance service providers.

The LT4670 builds on the success of its LT4610 predecessor which was developed primarily for use in composite analog, composite digital and SDI environments. In addition to its role as a timing reference, the LT4670 incorporates a range of tools supporting internet protocol content production, quality control and forwarding. Optional IP-related plug-in modules and downloadable software can be added if or when required to support evolving workflow.

Figure 1 shows the front panel and rear connection ports, including the SERR04 IP/12G SDI module. Local operation is via x/y pushbuttons interacting with a 24 character x 2 line backlit alphanumeric display. Dedicated pushbuttons are included for configuration, status and keylock. LED display lights indicate primary and secondary power supply on, and supplementary functions such as genlock/CW, GNSS, Precision Time Protocol in, PTP out and alarm.

Settings and monitoring can also be performed via a web browser with the LT4670 connected to a PC. Figure 2 shows the GUI home page.

Operating from 150 watts at 100 to 240 volts AC, the LT4670 can be slaved to incoming timing signals or used as a master sync generator.

Occupying the upper left section of the rear connection panel are a GPS input port, L-SYNC input, CW/IPPS port, two PTP ports (SFP/SFP+) and four 3G SDI 75 ohm outputs. Beneath these are an LTC/Remote port, Ethernet/Control port, six analog black 75 ohm outputs, two 75 ohm loopthrough genlock/CW inputs, plus wordclock, silence and AES EBU digital audio ports. AC mains connects to the right of the rear panel. A redundant power supply (LT4670SER11) can be integrated. The power supply unit and fans are hot-swappable. A remote connector can be used to load presets and transmit two alarm outputs.

Control is based on SNMP. An alert is issued when an error is detected. It is also possible to control the instrument via HTTPS/HTTP and REST-API. The LT4670 can be used as an NTP client to set the internal clock time for an NTP server. Up to 10 presets can be saved in flash memory. For operational convenience, registered presets can be recalled to always start up with the same settings.

Standard LT4670 toolset

The standard LT4670 toolset includes:

• Six independent analog synchronous signal outputs plus digital audio outputs, wordclock outputs and linear timecode in/out.
• Genlocked black burst signals and tri-level sync pulse generation.
• Stay-in-sync function maintaining output stability in the event of an error in the genlock signal.
• Slow-lock stabilization when returning to genlock from stay-in-sync.
• 48 kHz wordclock signal output synchronized to incoming video.
• Synchronous control between devices (L-SYNC).
• Preset and memory functions.
• Hot-swappable power supply and fan units to ensure workflow continuity.
• Battery-protected real-time clock.

Test patterns

Video test patterns available as standard in the LT4670 include 12G, 3G and HD 100% color bar, 75% color bar and multiformat color bar, check field, flat field white 100%, white 50%, black 0%, red 100%, green 100% and blue 100%.

The 525/59.94i SD test pattern set comprises 100% color bar, 75% color bar, SMPTE color bar, check field, flat field white 100%, white 50%, black 0%, red 100%, green 100% and blue 100%.

The 625/50i set comprises EBU color bar, BBC color bar, check field, flat field white 100%, white 50%, black 0%, red 100%, green 100% and blue 100%. Color bar patterns can be switched automatically and displayed for durations of 1 second up to 255 seconds in up, down, left, right or combined directions.

User patterns can be imported as 24-bit full color bitmaps or 24/48-bit uncompressed TIFF. Supplementary text pattern display features include safety area markers, ID characters, logo marks, moving box, circle, timecode and image overlay.

Audio test signals

48 kHz AES/EBU audio tone and silence can be sourced from the rear of the LT4670. The configuration menu allows individual control of channels 1 and 2 silence, 400 Hz tone, 800 Hz tone and 1 kHz tone, as well as tone levels in dBFS. Click sounds for checking lip-sync timing can be set to 1 second, 2 seconds, 4 seconds or muted. Controllable parameters also include 20/24 bit AES depth and pre-emphasis mode.

Timing-related outputs

Various output signals can be synchronized with NTSC/PAL black burst and HDTV tri-level sync. NTSC/PAL black burst with field reference pulse and NTSC black burst with 10 field IDs are also supported. 10 MHz CW lock is supported.

Six analog video sync signals can be output. The phase of each output can be adjusted independently. NTSC/PAL black burst signal with field reference pulse and NTSC black burst signal with 10 field IDs are supported.

The LT4670 can also output a 48 kHz wordclock signal synchronized with video signals.

Timecode control parameters include timecode insertion on/off, timecode timing, lip-sync interlock and wordclock timing. The timecode generator can operate in free-run mode based on internal time information. Based on the NTP server, LTC, VITC, GNSS (SER01), or PTP (SER03) time information, it can embed the LTC3 system output and analog video sync signal output in VITC, as well as the SDI (SER02/SER04) output in ATC (LTC/VITC). Three independent linear timecode outputs are provided. An offset time can be set for each output with respect to the frame rate and reference time.

In a main-plus-redundant system, L-SYNC can be used to synchronize the main and backup devices to a single analog video sync source. Synchronized time outputs are PTP (hardware module SER03), LTC, black signal (VITC), SDI signal ATC (VITC/LTC) (hardware module SER02/04), AES/EBU signal and NTP.

Optional expansion modules

The standard LT4670 toolset can be supplemented by hardware options such as GNSS synchronization. There are two independent PTP generators. PTP synchronization, 4K 3G-quad-link, 3G-SDI, HD-SDI, SD-SDI and 25G-IP/12G-SDI test signal outputs are accessible in any combination, allowing optimal management of synchronous systems. GNSS synchronization lock is obtained from GPS, GLONASS, GALILEO, BDS and QZSS.

Also available is a software option providing 4K 3G-quad link 4K output in conjunction with two LT4670-SER02 hardware modules. In addition to internal patterns such as the color bar, SD and HD (2K) user patterns can be output. ID characters can be overlaid at any position on the display. In addition, ID characters can be scrolled horizontally or displayed in a blinking state for checking whether the display has frozen. 24-bit full-color bitmap data can be overlaid as a logo mark at any position on the display at 640 × 480 VGA resolution. Figure 3 shows LT4670 back panel and hardware options.

The 25G-IP/12G-SDI option provides four independent HD to 12G 4K outputs, plus two 25G ST2110 outputs. Each output can deliver up to four IP flows. The PTP leader option supports the Precision Time Protocol defined in IEEE1588-2008 V2 and operates as a PTP grand master. SMPTE2059, AES67 and General profiles are supported. The PTP time source is obtained from the internal clock, NTP server, GNSS, VITC, or LTC.

When a host PTP grand master is present in the system, the PTP follower function option operates as a PTP follower and can function as a PTP leader for lower devices. Figure 4 (left) shows the LT4670 in PTP1 and PTP2 follower mode and (right) functioning as leader and follower.

Since two PTP engines are provided, a PTP system can be constructed for each of them as an independent grand master. The two engines can be used as followers. The leader can be selected automatically or arbitrarily by the user. It is also possible to use one engine as a follower and the other as the leader.

When genlocked to the analog video sync signal or HDTV tri-level sync signal, the local PTP function obtains time information from an external time source, such as a GNSS or NTP server. It can adjust the time according to the phase information of the genlocked sync signal and redistribute the PTP time.

PTP-compatibility (option LT4670-SER03) allows operation as a grandmaster. The PTP reader (master) function can select a reference from PTP, GNSS, VITC, LTC, NTP or internal time. PTP follower (slave) function is supported. Two PTP engines allow the construction of PTP systems in independent networks. Up to two RJ-45 SFP modules or two 10 GbE SFP+ modules, sold separately, can be used. PTP can be synchronized to an analog synchronous signal and the time can be obtained from an external time source such as GNSS or an NTP server. PTP synchronized to an analog synchronous signal can be output.

The L-SYNC mode allows synchronous control between devices (Figure 5).

A stay-in-sync function is used if there is a loss of genlock input. There is also a slow-lock function to reduce the shock that occurs when genlock is performed again based on stay-in-sync. Both are shown in Figure 6.

IP signal generation and network synchronization

The IP transmission standard is SMPTE ST 2110-20/30/31/40. Option LT4670-SER04 (25G-IP/12G-SDI TSG) can generate 2K and 4K video signal test patterns. ST-2022-6 is also supported. For IP signals, up to four flows can be output per 25G port. IP test patterns specified with SDI outputs are output. Video and audio test signals are generated in sync with SMPTE ST 2059 PTP.

Summary

The LT4670 sync pulse and test signal generator gives broadcasters and broadcast-related service providers the ability to operate efficiently in today’s SDI/IP production environment plus the freedom to expand the toolset to match their evolving operational requirements. Building on Leader’s 70 years of product development and manufacturing experience, this instrument combines high operational precision, versatility, ease of use and robust build quality.

* Steve Holmes is a Solutions Architect and Application Engineer at Leader Instruments Corporation, USA, focusing on SMPTE 2110 IP Video, PTP, monitoring, 4K, HDR and video test solutions. Steve has over 35 years of video application engineering experience including 21 years of video application engineering with Tektronix and 21 years with GTE/Verizon installing, teaching, engineering and managing video and CATV systems.