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發表於 2015-1-21 17:51:05
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本帖最後由 steveha 於 2015-1-21 17:52 編輯
Some updates on discrete R-2R from soekris (wa, it will support DSD on next firmware ) :
So what can the Soekris dam1021 Sign Magnitude R-2R DAC do now:
1) It plays everything over I2S, tested up to 192K but should do 384K.
2) It plays at least to 96K over SPDIF Toslink, and probably up to 192K over SPDIF Coax, but have problems generating test signals as that require software that actually works doing ASIO with channel select, my EMU-0404 use ch 1-2 for analog, ch 3-4 for SPDIF....
3) Automatic detect and support for digital De-Emphasis, for those old CD's.
4) Full set of relative simple and short FIR filters for all rates, but supports filters with up to 1016 coefficients at 48K. Docs and Software Utility to change them included, can also load bypass filters for NOS use. But after seing the ugly spectrum I don't recommend NOS....
5) Digital Volume Control, from -90 to +15 db in 1 db steps, both using a simple potentiometer and control codes over the serial port.
6) Input Selection, Automatic or Manual using control codes over the serial port.
7) Reclocking FIFO with automatic clock tracking works like a charm, syncronize to < 1ppm at anything withing 1% range, and then tracks using a software PLL with 0.02 Hz Lowpass Filter and with 0.02ppm step changes.
8) Tested with 7W toroid transformer. Measured 0.4V PP Ripple on input capacitors, couldn't hear anything but did see 50 hz at -135 db, most likely things going into the measurement cable as it changed when moving things around...
9) Everything can be updated by downloading over a standard PC type serial port.
Functions waiting for next firmware release (which should be soon):
1) DSD Support, should be relative simple, more a question about test setup with software and sound files....
2) Cascading for Digital Crossover use, the 14 pcs IIR Biquads are there (needed one for De-emphasis), and I want the function for my own speakers. If I can figure out how to calculate coefficients without trig functions then it can probably fit into the 32Kbyte in the uC....
3) Cascading for Balanced use.
And whatever I forgot to mention....
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