18-11-2018, 08:30 AM
Further thoughts.
If you're combining vision and sound digitally then the total of the 2 of them mustn't exceed the DAC's range. It's a 14 bit DAC so the total range is 0-16383. Without doing the sums properly I think you could use half of that for vision, leaving the other half for sound. Although unmodulated vision carrier is 6dB below peak white, at 100% mod the peaks would be equal to peak white.
Hence the vision levels would be 0 for sync tip and 8191 for peak white. The unmod sound carrier would be 4096 p-p. Add them together to get the final result.
I admit I haven't sat down with pencila nd paper to do the sums properly and it would be a good idea to do so. However, it's easy to play with the parameters in a FPGA so if you get it wrong it's no problem.
If you're combining vision and sound digitally then the total of the 2 of them mustn't exceed the DAC's range. It's a 14 bit DAC so the total range is 0-16383. Without doing the sums properly I think you could use half of that for vision, leaving the other half for sound. Although unmodulated vision carrier is 6dB below peak white, at 100% mod the peaks would be equal to peak white.
Hence the vision levels would be 0 for sync tip and 8191 for peak white. The unmod sound carrier would be 4096 p-p. Add them together to get the final result.
I admit I haven't sat down with pencila nd paper to do the sums properly and it would be a good idea to do so. However, it's easy to play with the parameters in a FPGA so if you get it wrong it's no problem.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
