Several years ago I had the idea of obtaining an Interface USB Stick for SPDIF output and Input. I wanted to equip my audio stack with a codec for playback and record alike and optical fiber wire is just a cool way to transfer the signals as it also provide an absolute galvanic isolation.
There are hundreds if not thousands of kits and modules available that provide an output via this chip, but none could be found that provides an HD capable input path. So if it does not exist I gonna have to do it myself (and maybe this gonna be my first seller ;).
The chip is from the Galactic Far East Cooperation and they don’t provide very much of info beside the minimum datasheet for basic wiring. Nothing about the settings, config tools or if it’ll need an eeprom. The only way is to get a few and try it. Yesterday was the day to finally know if it works or if I blew 50 € into the wind. Here’s my evaluation circuit:
Result: It Works!
But not out of the box as the standard windows driver does not support Audio Class 2.0. Though I could select 24 bits resolution, the sample rate could not be set higher than 48kHz. After Hours I found a driver package that installs it as TeraDak X2 link and it also provides a control applet that let it switch to 24/96 for playback and record:
I do not yet know if it really can do playback and record at 24/96 at the same time as I’ve read that this exceeds the 12mbps of USB 1.1 ?! Let’s see…
I looped back the output into the Input, started a singal generator and analsyed the input – or tried to as I could not start the record device in 24/96. So I went for 16/96 and got a dithered signal but at least without signs of resampling. Then I set the analzer to grab the samples in 24bit (the device still at 16bit) and got a clean signal, but the lower 8 bit were zeroed. That means that the Chip correctly receives the 24bit stream and the driver delivers at 24bit, but the transmission over the usb Interface back into the pc is cropped to 16bit!
So I’m now hoping to get an answer from GFEC for support or the whole project is doomed for failure and the ICs where bought in vain 🙁
Maybe I’ll try the Bravo SA9023 that shall be pin compatible next.