There’s a lot of jargon and marketing fluff when it comes to any sort of audio equipment. Particularly in “HD music” since there’s often the need to justify the premium prices for standalone DACs.
If a cheap $15 dongle claims it can do 92KHz 24-bit sound, what’s the advantage of a $100-500+ unit, right?
I’ll elaborate further in this post, but as a quick analogy to answer that, consider this.
Imagine taking a cheap $5 microphone, keeping the gain way too high, and talking loudly into it so the audio is badly clipped, distorted, and sounds terrible. But imagine that in the recording app you were using you’d told it to record in 24-bit quality.
What you’d end up with is a high bitrate and very large audio file full of awful recording. The 24-bit did not guarantee the recording was… well recorded.
In the same way, a DAC saying it can decode in 24-bit, 192KHz or beyond says little of its ability to turn that signal into a good sounding analog output to your headphones. It only means it can process audio files with that much audio data in them initially.
Many built-in audio chips on computer motherboards make claims about 192KHz 24-bit sound, yet the sound output is weak. The bass is flat, and the instrumentation lacks finesse. In fact, I would much rather use a high quality DAC at regular ol’ 44.1KHz 16-bit than a cheap 24-bit DAC.
CDs themselves that popularized the 16-bit audio format have plenty of detail — far more than any MP3 most people listen to. It’s plenty enough to take full advantage of any hifi amp and flagship pair of headphones.
Look For The Amp’s mW Power Rating. Will It Drive High Impedance Headphones?
Most small headphones, like earbuds, have a low impedance and can be easily driven from any 3.5mm jack. However, most high-end headphones are comparatively high impedance, meaning it takes more power from the amp to achieve the same volume level.
The upside is that the detail and presentation of those types of headphones are significantly better.
But this also means that any standalone headphone amp we’re using needs to be powerful enough to drive demanding headphones. In part, you’ll base this choice off of the impedance of the headphones you’re using.
Are they 150 ohms? Most headphone amps worth their salt will drive them.
250 ohms? Make sure the amp is capable of at least 2V, or 50-100mW.
For very demanding headphones into the 300-600 ohm range, aim for several hundred mW just to ensure it has the proper headroom.
Bear in mind that all amps introduce harmonic distortion into the signal once volume output goes over 80% of the amp’s capacity. Some will handle this better than others, but it’s still preferable to stay below this threshold.
Ideally you always want an amp more powerful than needed so you never need to turn it up that high, and the signal stays clean.
Compatibility
For the most part this isn’t a big concern. In some cases, like with the Sound BlasterX G6, it’s a good bang for the buck USB sound card with a DAC and headphone amp built in, buuuut…
It requires Creative’s software to use all of its features. When I first got the sound card I was a Windows user so it was no problem. But after switching to Apple, while it still works when plugged in, there is no software to control its advanced features or use its EQ.
When used on a MacBook or iPad, the Sound BlasterX G6 is basically a straight DAC and headphone amp. Which works ok for me most of the time, but something to be aware of. It’s a real failing of Creative as a company not to even offer Mac software.
I use it now because I already have it, but would not buy that sound card new at this point knowing I wouldn’t get half its features.
Otherwise, just make sure you can use whatever connection ports the DAC or headphone amp you’re looking at uses. If it has an optical input, do you have another device that uses that? If it’s USB, is it the type you’d prefer? Some devices are still on Micro USB, while others have adopted the modern type C connection.