If you've ever plugged a pair of headphones into a phone or computer to listen to your favorite tunes, you have a digital-to-analog converter (DAC) to thank. Often mentioned in the same breath as an "amplifier," both work directly with each other in order for you to listen to digital music files from services like Spotify, Apple Music, iTunes or Tidal, on your headphones or speakers.
But why do you need a gadget to convert digital to analog anyway, and why do companies sell seperate DACs you can use instead of the one that's already in your gadget?
The signals your audio devices make, whether they are digital or analog, aren't really fit for listening. These faint electrical messages are primarily a way to transmit data from one component to another, whether that's from a phono cartridge to a speaker, or a hard drive to a pair of headphones. Amplifiers are crank up analog signals to a magnitude that they can actually come out of your headphones or speakers at a reasonable volume.
But amps can only work their magic on analog signals. The DAC's job is to convert the digital signal (the ones and zeroes that make up your digital device's internal thoughts) and convert them into an analog signal that the amplifier can supercharge by adjusting the electrical characteristics of that signal in ways that only work in analog. Yes, this means if you're not listening to a digital source, there's no need for your system to have a DAC.
Most manufacturers combine headphone amps and DACs into one component. For example, Schiit Audio's Fulla 3 ($99) and Audioengine's D1 ($169) both combine an amp and DAC into one component that's designed to boost your computer's audio. In the smartphone audio realm, AudioQuest's DragonFly Series of headphone amplifiers-and-DACs are some of our favorites.
The difference between a good and bad DAC is also pretty straightforward. The best DACs are able to do two key things. First, they can convert audio files of a higher-resolution — such as 24-bit/192kHz or even 32-bit/384 kHz, both of which are higher-resolution than a CD quality (16-bit/44.1 kHz). Second, they can do this job on a larger variety of specialist audio files, such as this DSD, MQA, ALAC, so it doesn't really matter what device (smartphone or computer) and music service the listener is using because the DAC will play the highest resolution audio.
The reality is that pretty much any computer or smartphone you buy, it's going to come with a built-in amp and DAC; otherwise you wouldn't be able to listen to music from its speakers or plug in your headphones. That said, the built-in DAC/amp isn't usually very good.
A good way to tell if you should consider upgrading to an external DAC — or even a DAC/amp — is if you're hearing any extra noise in your headphones or speakers. Whether it be a hum or buzz or some kind of static noise, it's some introduced sound that you know shouldn't be there.
That said, you probably don't need to upgrade your DAC/amp if you're using cheap headphones or speakers. Or if you're not listening to high-resolution audio files. This is because your audio is only going to sound as good as the weakest link in your audio chain. (This is why it also doesn't make a lot of sense to plug really expensive headphones directly into your laptop or smartphone.)