[Packdemon]

Does something like this exist. I don't know anything about optical cables, so there is something obvious that I am probably missing. All I understand is that digital optical cables have digital in their title, and that USB is a digital serial bus. So they should be able to connect without a converter, right? So, why do cables and adapters like these exist - http://www.amazon.com/dp/B00T8HWUVS   http://www.amazon.com/dp/B0002MQGRM - when 3.5 is analog and optical is digital, or when I can't find a single digital to optical anywhere (with my understanding should exist)? Please, I want to learn more.

 

[ClieOS]

  Does something like this exist. I don't know anything about optical cables, so there is something obvious that I am probably missing. All I understand is that digital optical cables have digital in their title, and that USB is a digital serial bus. So they should be able to connect without a converter, right? So, why do cables and adapters like these exist - http://www.amazon.com/dp/B00T8HWUVS   http://www.amazon.com/dp/B0002MQGRM - when 3.5 is analog and optical is digital, or when I can't find a single digital to optical anywhere (with my understanding should exist)? Please, I want to learn more.

 
Because TOSlink / Optical is not just 'digital'. It is encoded in an audio format called DAT and it is based on S/PDIF (*Sony / Philips Digital Interface Format), or more correctly AES/EBU. It is also one way only. On the other hand, USB is neither specifically designed for nor encoded in any audio format, but is more for an an universal two-ways digital communication between computer devices. They are fundamentally two very different things, even if they are both using some kind of digital signaling. To say optical and USB are the same thing will be like saying vinyl should be able to play inside a cassette player since both are analog recording.
 
A 3.5mm optical adapter exists because some devices (i.e. macbook) have a hybrid 3.5mm output which there is an optical port hidden inside the 3.5mm analog jack. In other wards, the same jack is used for both analog and optical output at the same time, so you need an adapter to 'extend' an regular optical connector to reach further inside to get the optical signal.

 

[obobskivich]

In addition to what ClieOS said, you *can* get adapters that will take USB from the computer and provide TOSlink output (they're often sold as "USB digital transports" or some similarity). You can't go "the other way" - e.g. taking a TOSlink from a CD player, and "converting" it to USB to feed into a "USB DAC" or similar, however there *are* USB-eqiupped devices that take digital input as well as output. USB is a digital bus, and allows connection of various kinds of devices, including audio adapters. It's more accurate to consider a "USB DAC" as a "USB sound card" but that term has fallen out of style in recent years. A popular example of something that allows input and output is the E-MU 0404.

Random technical note: DAT refers explicitly to digital tape, not TOSlink (IEC 60958 (the IEC standard that describes AES/EBU and S/PDIF) Type II Optical Fiber, if you want to get really nitpicky). Similar optical fiber is used for ADAT Lightpipe, but Lightpipe is an entirely incompatible standard.

 

[Packdemon]

Thanks for the help to explain it to me you guys. The real reason I wanted to know about all this was so that I could hookup a usb amp/DAC to my cousin's PS4's optical output, so that way he could use high impedance headphones while playing his PS4. I'm still stuck on how I'm going to do that to be honest.

 

[obobskivich]

You can get a TOSlink capable DAC and then feed that into an amplifier, or get a DAC/amp that takes TOSlink. Either way set the PS4's optical out to PCM.