I’m NOT an expert on this…
The Realtek Optical out goes from my PC to DAC
… Wasapi Shared mode result in a bit perfect capture? As I understand this will be done entirely in the digital domain using internal Wasapi loopback.
Most streaming is compressed, and Windows is going to decompress or otherwise convert it to make it playable on your hardware.
There are apparently ways to play bit-perfect streaming audio, but I don’t know about capturing/recording it.
Most streaming is compressed and Windows is going to decompress or otherwise convert it to make it playable.
WASAPI Exclusive mode is supposed to play bit-perfectly and assume it can record bit-perfectly from an ADC or audio interface.
Because of licensing, Audacity doesn’t “ship” with ASIO support. You can add ASIO support if you are a programmer and you can compile Audacity yourself.
ASIO is hardware drivers so it should be unrelated to streaming capture. But it may be impossible to “capture” ASIO playback like with loopback.
“Regular” WASAPI, DirectSound, and MME will all resample when necessary during recording or playback. That way, any-old soundcard can play 24/192, etc. It’s for compatibility, just like you can view a high-resolution image on any-old monitor. The drivers take care of any necessary conversion without telling you.
The same is also true with loopback, plus loopback can play a mix of audio sources, which obviously isn’t bit-perfect. But I wouldn’t expect it to change the sample rate if Audacity is set to match the streaming sample-rate.
No matter what you’re using the bit depth will be re-sampled to match your DAC or ADC. You can play 8-bit, 16-bit, or 24-bit audio no matter the capabilities of your DAC. For example, if it didn’t up-scale 8-bit data it would be too quiet to hear on a 24-bit DAC. That’s also true with ASIO.
…Plus, you’re not supposed to be pirating streaming audio. Most of it is copyrighted and it’s a violation of (most) streaming agreements. If they wanted you to have a personal copy, there would be a “download” button. With “regular music” the artist gets a fraction of a penny every time it’s streamed. If you pirate it, they only get a fraction of a penny once. If you buy a CD or MP3, the composer and the performer (or their heirs or current copyright holders) both get about 5-10 cents.