I need a USB Sound Card with digital input

This will most likely work for you, and if the card doesn't support Linux (doubtful) you can return it?
https://www.amazon.ca/Audio-Adapter-External-Sound-Digital/dp/B06Y27TDJ9
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https://www.amazon.ca/LiNKFOR-Digital-Converter-Bi-Directional-Splitter/dp/B07QTP7FX5/ref=sr_1_5?crid=39A0GPK34VM59&keywords=optical+to+coax&qid=1654451122&sprefix=optical+to+coax,aps,73&sr=8-5
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The Sound Blaster Extigy has optical and coaxial inputs. I just googled and it seems that it can be made to work with Linux. I don't mess with Linux/programming so no help on how to. But these can be found cheaply on the used market. I think I paid $5 at a local thrift shop
 
diyink makes a multichannel USB card that can be configured for I2S input and or output.

Other than that many USB recording interfaces can accept SPDIF digital inputs, but those inputs are most likely going to be resampled via ASRC. In that case they would not be 'bit-perfect' inputs.
 
The only one that I remember (because I own one) is the M-Audio Fast Track Pro. It has coaxial out and in. I've seen plenty with coax or toslink OUT, but coaxial input is rare. Hundreds? I haven't seen them. There might be a few in the pro market, and above the budget stated here.
BTW, it is bit perfect, I tested it.

I did own one of those little eBay specials that Kodabmx linked to. It's was just "OK". Don't remember ever using the Toslink input.
 
diyink makes a multichannel USB card that can be configured for I2S input and or output.

Other than that many USB recording interfaces can accept SPDIF digital inputs, but those inputs are most likely going to be resampled via ASRC. In that case they would not be 'bit-perfect' inputs.

I've seen you say this a few times but it does not match my experience. What interfaces have undefeatable ASRCs? Majority of the ones I've dealt with (admittedly all consumer/prosumer stuff) do not have ASRCs and if they do they are optional. To be honest I wish more had ASRCs to simplify clocking with multiple sources.

MOTU Ultralite Mk5: SPDIF input, TOSLINK/ADAT input, no ASRC
Focusrite 18i20 2nd gen: SPDIF input, ADAT input, no ASRC
Okto dac8 pro: AES input, no ASRC
RME Fireface 800: SPDIF input, TOSLINK/ADAT input, no ASRC
miniDSP USBstreamer: TOSLINK/ADAT input, no ASRC
miniDSP MCHstreamer: TOSLINK/ADAT input, no ASRC
Apogee Ensemble (Firewire): SPDIF input, TOSLINK/ADAT input, optional SRC
MOTU 896: AES input, ADAT input, optional SRC on AES input only

Michael
 
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diyink makes a multichannel USB card that can be configured for I2S input and or output.

Other than that many USB recording interfaces can accept SPDIF digital inputs, but those inputs are most likely going to be resampled via ASRC. In that case they would not be 'bit-perfect' inputs.
I don't understand at all ASRC but I think it may not be necessary if I am putting SPDIF digital in and wanting digital output to USB. Seems there does not need to be much sampling.
 
Automatic sampling rate convertion... Usually handled by the OS anyway.

It is actually asynchronous sample rate conversion, meaning that the incoming digital stream is reclocked using the internal clock of the interface.

Most interfaces have a variety of clocking options (internal, SPDIF, ADAT, AES, word clock) and if you do not have an ASRC and are using a digital input you need to clock the interface from your digital input unless you have your source slaved to the interface. Without selecting the appropriate clock source you will have dropouts.

If you have an ASRC in the interface you can set the interface clock to internal and it will handle any digital source without issue.

Below is a great thread explaining the theory behind ASRC.

https://www.diyaudio.com/community/threads/asynchronous-sample-rate-conversion.28814/

Michael
 
It is actually asynchronous sample rate conversion, meaning that the incoming digital stream is reclocked using the internal clock of the interface.

Most interfaces have a variety of clocking options (internal, SPDIF, ADAT, AES, word clock) and if you do not have an ASRC and are using a digital input you need to clock the interface from your digital input unless you have your source slaved to the interface. Without selecting the appropriate clock source you will have dropouts.

If you have an ASRC in the interface you can set the interface clock to internal and it will handle any digital source without issue.

Below is a great thread explaining the theory behind ASRC.

https://www.diyaudio.com/community/threads/asynchronous-sample-rate-conversion.28814/

Michael
Thanks, that explains it.