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apfelaudio / tiliqua

A powerful, hackable FPGA-based audio multitool for Eurorack.
CERN Open Hardware Licence Version 2 - Strongly Reciprocal
59 stars 4 forks source link

(SC3 only) `usb_audio` bitstream runs at 48.8kHz but advertises 48kHz #55

Open vk2seb opened 1 month ago

vk2seb commented 1 month ago

In https://github.com/apfelaudio/tiliqua/pull/38, I modified a whole bunch of things to add support for the -25K LUT SC variant. This included modifying the PLL configuration to use 2 PLLs instead of 3 (reduced accuracy on audio Fs, was 12.288 / 48.0kHz, now 12.50 / 48.8kHz)

I have a followup task to either A) use a resampler between the IO and the USB streams, or B) rewrite/remove all the old eurorack-pmod gateware and migrate it to Amaranth so the I2S logic doesn't depend on a precise system clock (probably use oversampling).

As an alternative, we could just remove video support from the USB audio bitstream, as no other example really requires these precise audio sample rates.

vk2seb commented 1 month ago

As of https://github.com/apfelaudio/tiliqua/pull/57 the high-res PLLs are back for SC2 (LFE5U-45)