USB to spdif that allows source (iOS) volume control?

[jjk1]

Hello all,
I’m looking for a usb c to spdif optical converter that will allow me to maintain volume control directly from my connected iPad or iPhone.
Ive got a smsl po100 and it doesn’t. The source is locked at max volume. My understanding is that there may be old firmware that will allow source (IOS) volume control on the po100 but I can’t locate it.

Are there any other options?
Coax and optical outputs would be nice but just optical would also be OK too.
Any recommendations?

Thank you,
JJK

 

[sonitus mirus]

You will probably run into the same issue, but here is another driverless converter that may behave differently.

Douk Audio U2 Digital Interface DDC with XMOS XU316 USB to SPDIF Conve

Features Lossless USB to S/PDIF Converter: Convert USB signals from PC, laptops, phones, tablets, and Raspberry Pi etc. to optical/coaxial outputs simultaneously with zero loss and no latency. Ideal for DACs, digital amplifiers, or home theater systems that only support S/PDIF input. XMOS...

doukaudio.com

 

[Pow1]

Hmm my basic understanding is that spdif mainly transmits the sound information, meaning you generally cannot control volume using it.

There are some cases where people can control volume if you set your device to output PCM. I’m not sure if there is such a setting on your phone but that could be worth a try. But then I believe you would also be reducing the bit depth

 

[phofman]

IIUC the deciding factor is what type of output terminal the USB audio device reports to the host driver. If it's SPDIF/some other digital type, the audio layer disables the master software volume control. It would be easy to check with e.g. the linux audio gadget which can be configured to report a specific terminal type https://github.com/torvalds/linux/commit/de2eb28cdb76df9ce7587e1c6552b169069af4bb + disabling the volume feature, i.e. configs c_volume_present + c_terminal_type https://github.com/torvalds/linux/blob/master/Documentation/usb/gadget-testing.rst#:~:text=mute control enable-,c_volume_present,-capture volume control . For terminal type IDs see https://www.usb.org/sites/default/files/termt10.pdf