How to Use a DAC With a PCby James Lee Phillips
When it comes to getting the best quality sound from your PC, digital-to-analog conversion is the single most important part of the audio path. Many people stick with the DACs that come with their PC, or at best enjoy a moderate upgrade by way of a sound card or an all-purpose external device. Using a professional or audiophile DAC can deliver significant improvements in your sound quality -- if you have the right connections and equipment to make the most of it.
Technically speaking, a DAC (digital-to-analog converter) isn't necessarily an audio-specific device, but an integrated circuit that turns binary bits into analog signals. An ADC (analog-to-digital converter) does the same thing in reverse, taking electrical input and turning it into PC-friendly digital data. In addition to audio applications, DACs and ADCs are used for photos, video and even radar and laboratory test equipment.
In the case of sound, the analog side of the conversion is the electrical signal used by amplifiers, speakers, headphones and microphones. If you're hearing anything from your computer, you already have some kind of DAC as part of the integrated audio on your motherboard, or on a PCI sound card. DACs are also part of any USB headphones, speakers or microphones that you may use. If your sound is coming from your digitally-connected monitor, HDTV or home theater system, there will be a DAC inside that device as well.
DAC and ADC functions are often combined in a single audio interface that may itself be called a "DAC" -- confusingly, the acronym is often interpreted as "digital/analog converter" or even "digital audio converter." Devices marketed as DACs are typically external audio interfaces which connect to the PC via USB, FireWire or digital audio cable, and provide not only digital audio conversion but also often amplification and sound-shaping features. Consumer-level DAC devices are basically external PC sound cards, ideally (but not necessarily) offering an improvement in sound quality from the built-in audio on your PC motherboard. Audio professionals may use DACs that offer high-quality microphone inputs and preamps as well as line-level inputs. Audiophile DACs may omit input features and instead focus on high-quality headphone or line-level output amplification.
DAC to PC
Many DACs will simply need to be connected via USB cable to a spare port on the PC. In many cases, the USB cable provides input, output and even power to the DAC unit. Some DACs offer other PC connection options such as FireWire, which can typically handle audio input and output but may not provide power, or S/PDIF digital audio connection via TOSLINK or RCA cable -- which will only provide audio input or output (but not both), and will not provide power to the device.
Once the DAC is connected to the PC, the next step is to attach the necessary equipment to the audio output. For consumer or audiophile DACs, this means connecting a set of headphones or powered speakers via 3.5mm or quarter inch jack, or connecting RCA cables to send the output to an external amplifier (a standalone device, or the inputs on a home theater or stereo system, for example). For pro audio DACs, you may also have the option of connecting quarter inch line level or XLR microphone inputs and outputs.
Using a DAC with a PC can certainly provide higher quality sound, but your results also depend greatly on the quality of the other parts of the audio chain. Connecting an audiophile DAC to a pair of mediocre headphones or speakers may not improve your listening experience at all. Beware of DACs that use an analog audio input on 3.5mm or RCA jacks -- the audio will still be processed by your (potentially lower-quality) computer's DAC, reducing or eliminating any benefit from the external DAC.
Digital Audio Quality
If your music files are poor quality to begin with (low-bitrate MP3s, for example), the DAC may sound even "worse" because the device is accurately revealing deficiencies in the sound that lesser-quality equipment failed to reproduce. If you find yourself disappointed in your DAC's performance, try testing it with different headphones, speakers and audio files (FLAC or other "lossless compression" formats tend to work best).