The biggest new item is the new PCM upsampler, it uses fewer resources than the old PCM upsampler so that allows more freedom in doing everything else in the FPGA.
In the new upsampler I’m can get more accuracy in the coefficients (with fewer actual bits) because I know my data better than the Xilinx tools. I am also using a more sophisticated algorithm to round the coefficients. It tests for the best performance of the filter with each possible rounding of each individual coefficient iteratively - this takes some time.
I’ve widened the data path from the PCM upsampler thru the rest of the DSP chain to the SDM: I added another bit on the top (which should never be used, but…) and three more bits on the bottom (since I have them after the upsampling.) This doesn’t really add any accuracy (the input only has (at the best) 24 bits of accuracy after all) but it’s better than rounding/dithering back to 24 bits.
I’ve added a few general workarounds for ticks and pops: how much they help in any system depends on the source hardware/software.
- The FPGA now accepts PCM 0’s as DSD 0’s in DoP, this can smooth out DSD seeking in some programs like newer foobar2000 releases.
- I explicitly clear all buffers in the DSP path from the time a transition is noticed until the new data reaches the sigma delta modulator.
- I changed the ramp up time after a transition to around a second and made the “ramp down” time instantaneous. This will also help you to notice when the source/wires/network, etc. is causing skipping which could have just caused a little hash in the output. Now you’ll know you have something to fix.
The I2S input polarity UI would be too much of a distraction in PS Audio engineering at this time. I’ve decided to put it off another release… Sorry.
I rebalanced when some of the work is done in the FPGA to lower FPGA generated noise.
Paul and Darren have only heard the first cut at the first item (which always filtered to 22k even for 192k inputs.) I suspect that the newer versions of the first item and the other things will further increase sound quality.