The RB-DD4 is a 4 channel digital audio delay which allows 4 mono audio channels to be delayed independently or together. The delay for each channel is user selectable from multiples of common video frame rates, or from a user defined value via the serial interface. The unit is perfect for synchronising audio to video which has been delayed through processing latency. Using a front panel button, you can select which channel to delay. There is also an 'ALL' option which applies the selected delay to all channels. Then, using another front panel button, you can select the frame delay time and the multiple of frames to delay. Connectivity is incredibly flexible allowing three different connection types for each input and output including AES/EBU, S/PDIF and TOSLink. All three different output types can be used simultaneously. There is a front panel monitor socket which allows you to listen to each mono channel, selected via the front panel. Channel pairs can be monitored (1 & 2 or 3 & 4) using a rear panel stereo option. There is also an option to attenuate the monitoring by 12dB, selectable via a rear panel DIP switch. Audio presence is detected and displayed for each channel around the INPUTS 1 & 2 and INPUTS 3 & 4 buttons. The flexibility continues with numerous audio sync options. The digital audio output can be synchronized to either input, an additional AES/EBU reference input, a TTL wordclock BNC input or an analogue/SDI video feed if used with an additional RB-SYA or RB-SYD card. Additionally, the output can be synchronized to an internal master clock, which has a selectable frame rate. There are warning indicators on the front panel for loss of lock on both inputs and for the selected external sync. The selectable sync modes are as follows: Master Mode In this mode, the digital output sample rate is simply set and locked to the internal on-board clock generator. No sync signal is used or required. Auto Sync Mode In this mode, the digital output sample rate follows the selected sync input. When the sync signal is not present, the output sample rate will be set and locked to the internal on-board clock generator at the selected output frequency. Auto Lock Mode In this mode, no output will be generated until lock is achieved with a sync signal. The digital output sample rate now follows the sync input. If the sync signal is removed, the output sample rate will be set and locked to the internal on-board clock generator at the closest available frequency to the previous sync input. Slave Mode In this mode, the digital output sample rate follows the sync input. When the sync signal is not present, the digital output is muted. A powerful feature of the RB-DD4 is that by using the Sonifex SCi serial software, the unit can be programmed for different delay times, levels and switching functions so that you can program the unit for your specific application. A rear panel DIP switch configures the unit for serial control. Contact Sonifex for more information if you have a particular requirement that isn't covered by the RB-DD4 as standard. The RB-DD4 has been designed to have a passive signal path through the main input, so if power to the unit fails, signal inputs 1 & 2 are routed to outputs 1 & 2 and signal inputs 3 & 4 are routed to outputs 3 & 4. This is essential for applications such as installation at transmitter sites, where a power failure to the unit should not prevent the input audio signal from being fed to the transmitter. Please note that this is not true for the TOSLink outputs which are muted.