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Ports question - RCA vs USB vs Optical


Active Member
Jun 2, 2022
I’m new to dac amps and born into a word of wifi, Bluetooth and wireless everywhere.

I noticed there are RCA IN, USB B, USB C, Optical, Coaxial, Bluetooth. Do each of these have a different quality of sound?

Let’s assume you have all the cables and adapters available, and there are multiple devices with a variety of ports. And you just want to listen to music on macbook or PC.

Should USB be used first as a rule of thumb? Is it true RCA ports are weaker?


Major Contributor
May 27, 2021
Generally there is no difference. Digital data is digital data...

An optical S/PDIF connection avoids ground loops which can happen with an RCA connection. A ground loop can result in hum, but that's hum getting-into the analog circuitry.

Wireless connections also minimize the possibility of ground loops, but there's more chance of "glitching" (when the transmission gets interrupted or interfered with). You are also more likely to get latency (delay) but a few milliseconds of delay is only a problem if you are watching a video and the audio & video are out-of-sync.

I think USB can handle more formats because any conversion can be done with the software/drivers. For example, most stand-alone DACs can't decode Dolby Digital or any of the other compressed audio from DVDs & Blu-Rays but the USB should work just like any regular soundcard. But for the same reason, it might sometimes "hide" conversions or down-sampling.

Is it true RCA ports are weaker?
I'm not sure what that means with digital.... If the digital signal gets too week so the 1's & 0's can't be distinguished you've got "big problems". Digital doesn't usually degrade gradually or subtly like analog... You won't get a loss of volume or a loss of bass, etc., like can happen in analog. Usually It's clicks & pops, or dropouts, or it just doesn't work at all. My usual analogy is - One wrong bit in your bank account is just as likely to cause a 1 billion dollar error as a 1-cent error. (That's not exactly "fair" because one huge error in audio can fly-by, unnoticed and unheard, in microseconds.)

And you just want to listen to music on macbook or PC.
Sometimes the DAC built-into your soundcard/soundchip is good enough. ;) I think Macs have a pretty good reputation with PCs varying more, and sometimes you'll get noise. Usually noise is the only "sound quality" issue so if you're not hearing background nose a separate DAC is unlikely to hear an improvement.

Or, if you don't get enough power/loudness into your headphones, a DAC will usually have a better headphone output, or you might just need a headphone amp.
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Addicted to Fun and Learning
Aug 9, 2021
The OP did list "RCA IN" and "coaxial" separately, suggesting that maybe the "RCA IN" being talked about was analogue?


Addicted to Fun and Learning
May 22, 2018
By having a time-critical connection between the OS and the soundcard via an interface that doesn't even support DMA thus making it susceptible to dropouts during high interrupt latency. Oh wait that's the undesirable part.

The oft-quoted desirable parts are the support for higher bitrates. Which basically translates to support beyond 24/192. And of course, the USB device can become the clock master in an asynchronous USB connection altho in the grand scheme of things this doesn't matter since the audio frames are still generated by the OS and still need to be sent in a time-critical manner anyway.

Of course a huge part of this is because SPDIF is a format that hasn't been updated in years. The PHY of SPDIF today can easily go beyond 24/192 but nobody wants to design the rest of the system for higher formats.


Addicted to Fun and Learning
Nov 27, 2018
Modern USB is more desirable that S/PDIF optical/coaxial.
Modern USB allows the receiving device to control on when the signal (data packet) is sent, so will request at the speed it can handle.
S/PDIF optical/coaxial, the source device controls the sending of the signal, whether or not the receiving device is ready for it or not.
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