Digital to Analog Converters (DAC) are devices or parts of digital audio players that convert the digital data into analog audio waveforms. The digital “numbers” which are read off the software, such as CD’s, are converted into a particular voltage that represents the sound wave. This analog signal can then be amplified and fed into a speaker to reproduce the music. Okay, so that is a very simple explanation, but this article is more about their place in audio and what the benefits of these external DAC’s are.
As mentioned, there are two main types of DAC in hifi. Firstly every CD, SACD and DVD player has an internal DAC. In fact any device that stores or playbacks music (or movies, TV etc) from a digital format has a DAC. It is part of the circuit inside and the output can be seen on the rear of the unit as RCA sockets or balanced XLR outputs. Some disc playback units don’t have this at all; these are technically called transports as their sole job is to “transport” the discs. They have digital outputs that are connected to an external DAC. You may even be using your DVD as a transport if you have the digital output connected to an AV receiver; in this case the AV receiver has a DAC inside and converts the soundtrack to analog. Interestingly however, many players with internal DAC’s also have a digital output too. It is the latter we will look further into.
Now the reason to consider having an external DAC is simply that it may be better than the DAC circuitry inside your existing unit. It is a relatively easy way of gaining more performance but without the expense of a full upgrade. So how can a DAC make such a difference? There are several reasons, but the main premise for this is that you have a stand-alone unit dedicated to just one thing. It has its own power supply, so the power is not shared with any other parts of the circuit hence is usually cleaner and has more grunt behind it.
As they are stand-alone units, they have to perform on their own accord and the manufacturers will usually spend extra on the quality of the parts and on better design. The crucial analog output stage is where most of the extra quality goes and this has a direct effect on the sound. The digital part of the circuit often has extra features, like upsampling that can improve the sound as well. They often have different types of inputs, such as coaxial digital and also optical. So more than one source can usually be connected, such as a CD player or DVD player, and you can switch between them. Note that SACD digital outputs are usually security protected so you may get nothing out or a down-converted signal. This is to prevent making high-quality digital copies.
Some new units now have USB (universal serial bus) inputs; these are designed to be connected to computers (and possibly even memory cards) so any music you have bought online or copied (subject to copyright of course) can then be played back at often a much higher quality level than the computers soundcard. The USB input is often limited to the output of the computer. If using music off your PC, it is best to have the highest quality recording; that is with the highest bit-rate possible. This means the lowest amount of compression is used. Highly compressed music usually does not sound very good on a hifi system. It may however be fine for portable music players.
Other features of DAC’s can include re-clocking, where the digital signal is re-clocked and this can also add another level of improvement. What this means exactly is that the digital signal has it’s timing controlled inside the DAC itself. The other way is to generate a clock signal from the digital input itself and use that to drive the circuitry. Which is best can also depend on how good the clock in your transport is. Some also have headphone outputs and bypass features too. There are many brands out there but most come from specialised hifi companies. This is because DAC’s are regarded more as an audiophile device, not a mainstream product. Coupled with this they are usually only available from reputable hifi stores and online hifi dealers.
External DAC’s can vary in price from a few hundred to many thousands. As usual you get what you pay for. As you go up the line you get things like better circuitry, remote control, balanced outputs and extra features such as upsampling. As with any new hifi product, it is important to try it out with your existing gear. Generally they do not have issues with matching to other devices such as pre-amps; the outputs are just like any other CD player so the same sorts of rules apply. Find a dealer who will let you try it out with your own gear to make sure you like the sound; often they will give you a money-back guarantee. Also there is little point matching a cheap DAC with a high-end CD player, you will likely find that the original CD sounds better! But if the player is getting on in age but still works well, a DAC can give it a new lease of life!