seanadams Wrote: > > > At full volume you will get exactly the same output as with current > firmware. You can verify this by looking at the s/pdif data. If you > don't believe the bits, try a blind listening test. >
I just tried version 15 firmware and I don't see any difference volume wise with 48 so that is not an issue (I never said it was). What I do know is that at full volume the bits going to the DAC chip itself produce lower volume signal in my DAC than when I feed the same file over USB to my DAC, and I AM taking into account that its left justified not I2S. The S/PDIF interface does not have this issue, its something different between the data sent to the DAC and the data sent to the S/PDIF encoder. I also tried taking S/PDIF out into a S/PDIF to USB converter and recording that on the computer. The resultant file produces the same output direct to my DAC or sent back to the SB3. Because it is possible to deliberately make the analog out and the S/PDIF out have different volume levels (through a couple of different methods) I don't think its a correct statement to say that because the S/PDIF out has bit perfect output that data sent to the DAC is also inherantly bit perfect, if they were both connected to the same trace on the board you could make that claim, but since they are not I don't think it is a legitamate claim. >From everything I have been able to measure, somewhere along the line, either in the firmware or in the FPGA the data going to the DAC chip itself does not go up to full volume when the volume control is at full. I've been very careful to disble replay gain and set the preamp volume to zero in all these tests. Since the issue seems to only happen with the DAC data not the S/PDIF data it seems that its appropriate to look at whats different between them. Since I don't know anything about the firmware and this does also seem to show up in softsqueeze I'm going to do some poking around in softsqueeze code and see if I can come up with anything that makes any sense. There is something going on here, unfortunately I have no clue what it is. I'm trying to come up with some hopothesis and experiments to test them. Unfortunately winding up in the hospital and being flat on my back right know are making that slow going. (I'm typing with my laptop resting on my tummy right now!) There are two "issues" 1) volume is lower 2) sound quality is not at as good. Tapping into the data going directly TO the DAC chip and feeding that to my DAC (taking into accound left justified/I2S differences) does not sound as good as the same file sent to the DAC over USB, even when the analog volume has been adjusted so the levels match) I didn't even notice this at first. Other people found this out when I played my SB to DAC on thier systems. After I heard it in other systems, I did notice it in mine but its not as obvious. (this arrangement DOES improve some aspects of the sound (much lower jitter) and I was focusing on that) 1 is easy to measure 2 is not measurable. Softsqueeze has the same "quality degradation" as the bits to the DAC. Squeezeslave has higher volume and does not have the quality degradation (ie sounds as good as the same file sent over USB) My current wild stab in the dark guess is that there is something in the implementation of the volume control in both the firmware and softsqueeze (which of course is trying to emulate the firmware) which is somehow not getting to full value for the DAC but IS for the S/PDIF out. John S. -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=26002 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
