I've got some bad news: Those nice headphones and great speakers that you spent so much money on? They probably don't sound as good as they could. You spent the time searching for the best audio gear for your computer, and no one wants to get less than what they paid for.
Not sure what I mean? Let me explain. Sound that you play on your computer starts out as a digitally-encoded stream. The built-in digital-to-analog converter (DAC) in your computer converts those bits of data into an electrical signal that is, in turn, fed to the amplifier that makes the drivers in your headphones or speakers move and produce sound.
But by its nature, this digital-to-analog-conversion process isn't exact, so some DACs produce a higher-quality facsimile of the original recorded signal than others. The DAC built into your computer was likely chosen to fit space, power, and cost constraints, rather than for optimal audio performance. And your computer's built-in headphone amplifier, which is part of the headphone jack's circuitry and provides the juice that drives your headphones, was picked for similar reasons — and has similar drawbacks. Plus, these components are all sensitive to the sorts of electronic noise that pervade the inside of a modern computer.
If you've invested in quality headphones or upgraded your speakers, you can use an external DAC to help those components reach their full potential; many external DACs also include significantly better headphone amplification — you use the DAC's own headphone jack instead of the one on your computer. These upgraded headphone jacks give you tighter and stronger bass, increased clarity and detail, better separation of instruments and notes, and other subtle improvements that add up to an increased sense of pace and musical drama. Taken together, these changes bring you closer to your music.
Though many vendors offer large, AC-powered, audiophile-grade desktop DACs and headphone amplifiers, the best values for computer-focused DACs can be found in compact packages — the size of a deck of cards or smaller — that receive audio and power from your computer's USB port. I previously reviewed Arcam's $249 rPAC (4.5 of 5 rating), which impressed me with its build and sound quality. However, a number of similarly sized and priced models compete with the rPAC, meeting or beating its price, size, features, and/or sound quality.
I gathered six such products, ranging in price from $149 to $300. (My guideline: Don't spend more on a DAC than you did on the partnering headphones or speakers.) Each is small, uses USB for power and digital-audio input, includes a headphone output with analog volume adjustment (controlled via hardware or software), and supports high-resolution audio files up to a 96 kHz sample rate and 24-bit depth (some support 192 kHz/24-bit). Most are based around asynchronous USB technology, in which the DAC controls the rate of date transmission from the computer in order to reduce timing errors (called "jitter") that can cause audible and measurable reductions in sound quality.
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