chill wrote: > John, a couple of feature enquiries: > > - do you think that a future option for Gen1 might be an add on board > that allows external digital inputs to this DAC, so we can treat this > player as our system DAC as well? > - will the chip's programmable DSP allow us to implement some kind of > tone control/graphic equaliser and maybe even a full blown room > correction filter?
External digital inputs is tough. If you mean an S/PDIF input, it certainly can be done, the processor has receivers for this, but the clocking becomes an issue. Whenever you receive a digital in you have to worry about the clocking. I'm putting a fixed low jitter clock on this board, so we have three choices for syncing an external S/PDIF input, 1; use the internal PLL which syncs to the incoming stream, it will work but the jitter is much worse than with our low jitter clock. 2; use the builtin ASRC to resample to our external clock. 3; go with the "do a lot of buffering" scheme and output using the low jitter clock. With the large amount of memory available #3 is not hard to do, but you will have significant latency issues. If you can live with the latency #3 probably sounds the best. On your second question, yes indeed, that was part of my plan all along, that the DSP in the DAC chip could do equalizers DRC etc. There is one problem, it would just be for the analog outs. Looking carefully at the spec sheet I see the chip has an I2S OUTPUT that can be driven from various parts of the DSP system, so such filter could be sent back into the processor and routed out other outputs. This would probably be fairly easy for S/PDIF since it uses the same clock source as the DAC chip. But it's way complicated for USB out. The problem is that for an async USB DAC the average rate at which the data goes out the jack is controlled bythe DAC, NOT the low jitter clock on our board. Using a DSP in the DAC chip is a realtime process and it is going to be difficult to synchronize it to the rate the USB subsystem is sending data to the USB DAC. I suppose its theoretically possible to implement a second rate control loop using one of the on chip PLLs to feed the data in and out of the DAC chip, but that is getting pretty complicated. That brings up another issue, I don't think it's possible to have the USB output going to an async DAC at the same time we are sending data to the S/PDIF out or DAC chips. They are on separate clocks. No matter which one is given control of the data rate of the stream, the other is going to click and pop, UNLESS we use the ASRC or PLL route. \ There should be no problem having S/PDIF and analog outs going at the same time since thay use the same clock. John S. ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=97881 _______________________________________________ discuss mailing list discuss@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/discuss
