I have an older design using an ADAU1701, and we'd like to upgrade it to include consumer-grade TOSLINK (optical input), but I don't want to add too much cost. From my reading, this gets complicated, because the master clock for the ADAU won't be synchronized with the external source. So I assume I'll need an ASRC.
I see a few options -
1. Add a chip to convert S/PDIF to I2S as a slave to the source, then use an ASRC to sync the digital data into the ADAU1701. This seems quite complicated, but maybe there's a cheap IC somewhere that does all this?
2. Convert the S/PDIF into analog, which is mux'd or mixed to the ADAU analog input. This probably requires a receiver + DAC, so $$.
3. Switch to an ADAU1442 or similar (adds $5), which handles the digital side nicely, but requires a codec to retain my analog capability, so that's another $2 or so. The extra processing is nice but I don't really need it.
Given that this type of input is so common in inexpensive consumer gear, I'm surprised it's turning out to be so expensive - easily $5 plus the connector in quantity.
Any other options I'm overlooking?
Thanks very much. The DIR9001 looked interesting, as it can use its own clock, or the source clock, and switch automatically. Then the ADAU1701 would be a slave via I2S. I'm not sure how well-behaved the clock switching is, however, and whether the ADAU1701 will lock up during these transitions. It's only a $2 chip.
Maybe I should see just how bad these old AC97 codecs are..