FAQ		Rubidium Series: Time Code with 48, 50 and 60 frame rates

Time Code with 48, 50 and 60 frame rates

Picture rates of 48, 50 and 60 frames/s are possible with HD-formats that use "progressive scan" technology. When dealing with these formats, there are presently discrepancies in the SMPTE/EBU-standards concerning the implementation of Time Code. The SMPTE organization is presently working on a standard (i.e. solution) to this problem at various engineering meetings. Fundamentally, there are two different methods presently being debated. The first method developed by a group known as the “Purists”, simply demands a counting of all frames and therefore display of 0 to 47 / 49 / 59 frames. Unfortunately, this method leads to incompatible technical changes where the LTC must double its frequency. To technically accomplish this solution, a change in the bit structure will be necessary in order to be able to continue counting past the traditional amount of frames, which is not physically possible with all present systems being used today. Although it is argued by the purists that this change only concerns new systems with progressive scan formats, that will require a new updated studio-infrastructure anyway.

The second method called the “adaptive” solution seeks a simple transition for all current new formats as very important. This solution involves the utilization of the well-known field-decoding method (V1 / V2) per frame, now instead to be used with a pair of frames (i.e. two separate frames). Therefore with 48/50/60 frame formats, only each second frame would be counted and that the exact frame number could then only be distinguished by looking at their 1./2.- “field” value. This method would allow for most available systems to be adapted with only a few small changes enabling a relatively simple conversion to the various new frame rates. A disadvantage to this method is that LTC is generated only once per two frames and is therefore the LTC-ATC would only be available in every second subframe.

Present status of Alpermann+Velte Time Code Systems

Our HT and HV modules (Inserter / Reader / Generator) and PCL PCI HD reader cards with HD-SDI functionality presently use the second “adaptive” method, where the frame couple-counting with subframe-notice is being implemented. If you possess some of our first generation HT- and HV-modules, a firmware update to bring your module up to our newest specifications is available free of charge for download on our website.

Our generators such as our “GT-module” are synchronized to an analog blackburst and therefore is compatible with the second “adaptive” solution with V1 / V2. Our Time Code generator GT is available with tri-level synchronization possibilities (option), which will allow us to enable the “purists” method encoding frame rates. Please note that this method will only then become available, should the new encoding method be specified by the SMPTE so we can ensure that fully compatible systems will emerge. We can however offer anticipated customer specific "intelligent solutions" upon request.