1) CMEDIA.
Doesn't looks active, never reply to my emails, only resend that to their local agents in SHZ. Local agents are ignorant as usual in mainland-china, any tech question will take months of email ping-pong. Also, agents are crazy greedy, they asked me $5 for CM6642 bridge, which I found for $2 finally. The chip(6x5mm QFN) is quite handy just 4pcs 0402 external components required, single power rail 5V, 20mA at 24/44.1.
The chip contains OTP for the FW, and CMEDIA gave me win exe app to program IC by USB(BTW, the DLL used with the app was made by Realtek!). However, CM6642 contains the design defect, it has no CRC validation for audio packets, hence, any dust in the USB-C connector may cause a loud noise.
CMEDIA product manager said that they can't fix that defect by FW, hence, only the new silicon version may help. Actually, most USB audio bridges(but not XMOS) made on 8051 free core and state machine, hard-logic for the fast USB operations. The FW(8051 program code) may correct some functions but not all.
Pros: compact, low power, no external oscillator required(PLL from USB's 48MHz), single power rail. It doesn't need driver at all.
Cons: SPDIF output only with 24/192 limit. Near to zero support, design defective chip. A quite bad idea to go with cmedia in 2020..
2) XMOS.
All app info is opened, well documented. Good support forum, easy to start, easy to modify a custom FW(I spent a couple of days).
Cons: Expensive chips(XU208 PCM 32/384 DSD256 near to $10), no free Win driver. Huge power consumption, 24/44.1 about 110mA, just a lot of surrounding parts. absolutely not suitable for a portable purpose.
3) Realtek ALC4050, it is a combo, the same as CM6642 i.e. DAC+HPA + ADC, supplied with I2S port Off. 6x6mm QFN, single-rail power 5V, a few surrounding parts(5pcs 0402 caps and 1 res) needed to work as USB/I2S bridge. 32/384 DSD256. Core 1.2V, 18mA 24/44.1 consumption. Very low cost, $1.3-1.5. 64kB flash for the FW onboard. Widely used in the new PC motherboards and USB-C/3.5mm jack adapters.
Cons: Zero support, even to get I2S On is impossible(I can On/Off anything in CT7601 source code during a couple of minutes!). In the case if Realtek will offer its source code, it would be the most advanced USB/audio bridge for a portable purpose!
4) Savitech.
Cons: The most secret and most archaic tech at the same time.
Requires NDA to get FW USB programming app, I'm not kidding! )) It is so stupid when you can simply read the FW from the 24C256 where is FW located )) Their www was updated last time 2016, they never reply to your emails. I was sure if savitech simply bankrupt. All chips are 2011, requires 1.8V and 3.3V rails with terrible current, so you need to use buck convertor like with XMOS to make 1.8V >100mA.
Even reset is an external RCD circuit, and when I used the Power_good output of my buck convertor, savitech asked to return back their resistor-capacitor-diode circuit! Oh yeah, savitech will ask you for the schematic for the review! )) $5 for the SA9302/9312 32/384 DSD256(to be honest, I didn't see works DSD256 ever with that ICs, only 128). Need wait months to get your "custom" FW, where you actually can not ask for any serious customization at all just product name and LED behavior. Not easy to buy, also needed to fill the form, why you want to buy savitech ICs etc. I see no reason to consider savitech as a USB/audio bridge supplier.
5) Comtrue CT7601CR
actually it is not an ideal bridge as well but they give you the source code(8051 keil project) and free win driver too! All pdfs you can download right now. You don't need a host MCU because all that you need could be implemented by modifying the source code. The chip itself is more technic vs savitech(1.2V core, less current, no stupid external RCD reset etc) but not such advanced as ALC4050 yet. They have different ICs in different packaging, named almost the same CT7601.
I use 6x6 QFN 32/384 DSD256(DSD256 really works with Mac, Win, Android) $4.5. 1.8v and 3.3V rails required + one Xtall and few 0402 caps + SPI flash for the FW. Another CT7601PR in the pin2pin same case supports 32/768 and DSD512, as I know $6.5, and cheaper one CT7601SR 32/192 DSD128 $2.5. We asked Comtrue for the HID in/out which wasn't implemented, and they agreed to implement that if we'll give them the app to test HID functions with. Alive people, what can I say.
Cons: so far impossible to buy even in mainland-china. I've ordered 1KU and may offer it on my E1DA Aliexpress store.
6) Cirrus Logic CS46L41
seems needed only 5V as well, very low 24/44.1 current(almost the same current for PCM 384k and DSD128), about the same ALC4050 if not less. Requires external serial flash for the FW. 3x3 BGA case makes PCB noticeable more expensive due to .2mm vias. Also, needed one 22MHz oscillator.
Usually, CL offers two options for the cases so I guess CS46L41 QFN does exist too. About $5/pcs.
Cons: no application data available.
Epilogue:
Why many of those companies hide USB bridges from a public domain? I guess we should blame.. Apple inc. When they did delete 3.5mm jack from their iPhone, they created a huge niche for USB/3.5mm jack adapters. Now a lot of Chinese phones goes the same way and the niche reached a few hundred million adapters/year. Suddenly, tiny Taiwanese companies as savitech(I guess it is just a few people, 1-2 is enough to debug FPGA and order the silicon) either not too big US company as CL got the chance to make a big money until big players wake up like Ti, ST, On, NXP, AD. BTW, I've found on AD engineering forum info that AD testing their own high-performance USB audio bridge, hence, I'm right about why that topic so much hermetic today.
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