[sdiy] Does usb c alternative mode allow analog signals on the multi-purpose pins?

[Eric Brombaugh]

I bought one of those cheap USB C headset adapters as an experiment to 
see how well they work.

https://www.amazon.com/gp/product/B07XYQ2ZKH

Physically it's tiny - barely larger than the USB and 3.5mm connectors 
(plus short cable between them). Tried it out and it worked well, but 
then as I dug deeper it turns out that it's *not* passive - it actually 
has a full codec + amps inside. Plugging it in enumerates a device on 
the bus that's unrelated to my laptop's built-in audio:

ID 0572:1b09 Conexant Systems (Rockwell), Inc. Hi-Res Audio

Amazing.

On 11/17/22 02:31, cheater cheater via Synth-diy wrote:
> If you go to amazon, you'll find nearly infinite USB C to headset
> adapters following this standard, and they're as cheap as 4 euro.
> They'll probably work well, too - even the worst C plugs I've
> encountered on cheap cables are still very resilient. The mini jack on
> the other hand, I mean who knows, but it'll probably take a bunch of
> cycles. The more expensive ones are up to 10 euro, but not more.
> 
> On Thu, Nov 17, 2022 at 10:25 AM cheater cheater
> <cheater00social at gmail.com> wrote:
>>
>> Thanks for the pointer to the spec. Appendix A talks about passive
>> audio adapters from USB C to headset TRRS. That includes both input
>> and output analog signals on the pins of a USB C port.
>>
>> Glad that you linked me to the pdf, the last time I tried searching
>> for USB specs I found something completely different and it didn't
>> answer my question.
>>
>> On Tue, Nov 15, 2022 at 9:23 PM Chromatest J. Pantsmaker
>> <chromatest at azburners.org> wrote:
>>>
>>> "NOTE: Adopters may only use the USB Type-C® cable and connector to implement USB or third party functionality as expressly described in this Specification; all other uses are prohibited."
>>> From:
>>> https://www.usb.org/sites/default/files/USB%20Type-C%20Spec%20R2.0%20-%20August%202019.pdf
>>>
>>>
>>> On Tue, Nov 15, 2022 at 11:08 AM cheater cheater via Synth-diy <synth-diy at synth-diy.org> wrote:
>>>>
>>>> As in subject. Is there anything in the spec that speaks against this?
>>>> Where would one go in order to get a definitive answer to this?
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