I asked this question because I initially thought anyone with an high-end headphones are least likely to be affected if Apple removed headphone port from a Mac (because the included headphone port usually isn't powerful enough to drive some of the high-end models anyway, and many would likely to replace the DAC too, in addition to adding an Amp.)

USB also feels like overkill for an audio interface. It allows transfer of data in both directions, and introduces security risks if you don't fully trust the DAC you are connecting to, or worse still if the DAC is connected to a network/the Internet.

I'm not suggesting for a moment there is any audible difference between the two, but optical audio has always struck me as a 'cleaner' way to output digital audio.

I would be extremely annoyed if it were removed from the MacBook Pro.

On multi-tasking OSes with memory protection, everything that accesses hardware requires drivers; it's 'just' the amount of driver code that differs (which, for USB vs optical, probably is quite a big difference)

Also, originally USB didn't support isochronous channels at all, so one couldn't guarantee that one could send audio out continuously.

SPDIF also combines the clock and data in a single signal, it has more or less the same issues with jitter that USB does. Not that it matters since I'm not aware of a single proper study that indicates jitter is audible.

Often there is a receiver IC that will perform clock recovery and convert from S/PDIF to an internal digital audio format, I2S most commonly, to send it to a DAC IC. In this simple setup there generally is no more buffering than needed for operation of the pieces.

In more complex situations, either where the S/PDIF signal is being re-clocked or where the data on the S/PDIF line needs to be decoded, then they will be buffering.

To clarify some terms:

Re-clocking - the system detects the clock rate of the signal but does not use that clock as the reference, instead it will generate it's own clock at the proper frequency. Some buffering is needed here to offset drift between the clocks causing sample starvation.

Encoded data - S/PDIF (really AES3 for the most part) has a framed block transmission format not entirely dissimilar to a TCP packet. There is meta-data, frames, sub-frames, etc, it's not just 'pure audio'. Various formats can be stuffed into these data frames, like compressed audio data (5.1 Dolby Digital for example).

I try to steer clear of some of the more 'woowoo' audiophile stuff; but if a $10 amazonbasics optical spdif cable can do more to reduce noise than any thousand-dollar unicorn-dust copper cable on the market, I'm in.

In this case, I use a DAC combined with the Amp but honesty while I see the difference that an Amp brings, I don't see the difference of using a different DAC than apple's DAC (I've tried doing blind tests). So, I could see myself just using an headphone amp without using a DAC..

I've never used an external DAC, but it seems that the parent is weary of companies fucking it up with the usb drivers (or the firmware in the device) and introducing delays or artefacts in the audio stream. An optical to audio converter is easy, probably any third year EE could produce a working prototype.

There were some problems with old software and hardware that have been resolved for the past ten years or so, but USB audio could be problematic in the early 2000s. Optical was never really any better than FireWire in terms of latency.

Right. I'm really not an expert on this but my understanding is that with S/PDIF supposedly you have a control over the buffers on either side whereas with USB audio you are limited by the USB spec.

[1] I have literally never seen an isolated [2] USB charger for a car, and I've looked. You can fudge it using an inverter, an isolation transformer, and a 120V charger. I'm not talking about "my golden ears hurt" noise; I'm talking about "egads this music sounds awful and crackly" noise.

[2] By isolated, I mean a charger that provides galvanic isolation between its inputs and outputs. Some switching power supplies are isolated and some are not. Any charger that plugs into a wall plug and isn't polarized MUST be isolated because, if it's not, it'll zap you. The upshot is that your car's electrical ground ends up connected to some piece of copper in or near your amp, and car's electrical systems are noisy as hell. [3]

[3] Fun reading: http://www.newark.com/pdfs/techarticles/tyco/Auto_Network_AN... If you ever visit the NRAO in West Virginia, there's a big area where you're not allowed to bring a non-diesel car because they're so noisy.

1. i used all the usb ports on my workstation and don't want a hub

2. i use the usb and line-in analog inputs on my dac for portable devices, the optical one is permanently connected to my workstation.

3. optical feels 'native' in the operating system, it's just another output on the soundcard and doesn't require anything other than native drivers. this is probably wrong, but whatever.

I haven't gotten into the gritty details yet and have only been using it with TouchDesigner and ZVector Touch so far but it's fairly promising as a low cost, decent quality RGB+depth camera.

The first Tango phone from LG is far too big and underpowered but future Android phones could have this stuff built in unobtrusively. Couple that with better AR games (a new version of Pokemon GO, for instance) and Apple will badly need something similar to compete.