CM6327A datasheet doesn't say a lot about the typical application (in terms of circuitry around the chip) and I can only find some photos of commercial product PCBs on the Internet. It seems, thought, that CM6327A can be used without uC control and even without EEPROM (with the default product string, PID, VID [sounds fine to me, also not planning to use more than one mic on the same machine]), and judging by those photos, the circuitry around the chip is not too complicated.
Would be nice to take a look at some example design around CM6327A, though. Have you seen any out there?
They seem mostly interested in low-cost, high-volume consumer product manufacturers, so there's not great public documentation, especially for such a niche chip. We're lucky they publish datasheets. The critical thing missing here seems to be the default EEPROM settings, it's possible it just boots up muted and without an EEPROM. How to use the GPIO is also missing, and some PWRSEL pins are referenced but not defined. You could try e-mailing them, can't hurt. On the bright side, these chips are designed for absolute lowest cost in a typical application, which means a minimum of external components is likely required, so the EEPROM is almost certainly optional for a typical design.
I haven't seen any designs well documented; my own interest is on the high end side, so I've spent some time trawling CMedia for useful chips, but only actually used the CM6631A (USB UAC2 -> I2S) (and then just on a devboard, I decided to implement this function myself in the end since this requires 'firmware' that is not trivial).
Hey, it's a very interesting and pretty detailed article! Thank you for mentioning it.
The hardware design isn't even that complicated, but clearly it pushes some complexity towards software (firmware). I have nothing bad to say about this approach, and the project is cool 
, but I'd prefer a more analog design. Well, maybe because I have enough software development during work hours
With a digital mic, there's practically no analog at all! Intermediate option might be using a separate I2S ADC and a similar software design, but you're unpacking the microphone part more than the microcontroller part which would be largely the same.
The 'struggle' here so to speak is that low end, value solutions will be completely integrated with a fixed configuration (as you are finding that you generally get either just a DAC or a DAC+ADC, but not often just an ADC) like the CM6327A, but once you move away from that, there's too much configuration required for a fixed solution, and if you're going to need a micro anyway, you may as well implement the USB there too. There are still a couple products out there that bridge that gap (handle USB<->I2S but require an external micro for configuration), but not many. See CP2615/CP2114 (now NRND), or maybe SA9227 that is even less well documented than CM6327A.
You will find USB UAC1 app notes for most USB microcontrollers that contain an I2S peripheral, though.
I've done a fair bit of digging around this area, and if you don't want to use a firmware-based implementation, you don't have many options. Most integrated chips include DACs as well, and most USB-I2S bridges, which are few and far between anyway, aren't configurable enough for this.
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