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DACs: what is a DAC? And do you need one?

what is a DAC?

You may not even consider it, but most of us make use of at least one digital-to-analogue converter (more handily known as a DAC) every single day.

Built into the likes of computers, tablets and smartphones, the DAC is the fundamental key to unlocking the convenience of digital music. It converts the countless reams of digital information into an analogue signal that's intelligible to the likes of speakers and headphones – and the human ear.

Any device that acts as a source of digital sound – be it a CD or Blu-ray player, digital TV box, games console or portable music player – will need a DAC to convert its audio to an analogue signal before it is output.

Traditional amplifiers don’t handle digital information, speakers certainly don’t play digital information and our ears cannot interpret digital information – they all need an analogue waveform. Without a DAC, your digital music collection is nothing but a sizeable collection of “0s and 1s” (more on that shortly) that makes sense only within the digital domain. In short, DACs play a large part in making digital music worthwhile.

The biggest problem is the DAC circuits used in many devices are just not efficient enough to do justice to the original recording, so a DAC upgrade can be the simplest way to improve your digital music and really get the most from your system. Whatever your set-up.

What is a DAC? What does it do?

The sounds we hear on a day-to-day basis – traffic, instruments, that baby screaming on your otherwise peaceful commute – are transmitted in soundwaves, which travel through the air to our ears in a continuously varying analogue signal.

Analogue recordings were stored on the likes of shellac (and later, vinyl) discs, and later still magnetic cassette tapes - but the fragility and unwanted noise of these formats made way for something new. The CD was born, kickstarting the digital audio revolution in the process.

Cambridge Audio DacMagic 200M

Cambridge Audio DacMagic 200M (Image credit: Cambridge Audio)

Digital audio takes a very different approach to that of analogue. Digital music files are usually found in the form of Pulse Code Modulation (PCM), and are created by measuring the amplitude of the analogue music signal at regular intervals.

The value of the amplitude is represented as a binary number (comprised of 1s and 0s) and the length of this number is often referred to as bit depth. The timing of the measurement intervals is called the sampling rate.

When recording a standard CD, say, a sample is taken 44,100 times per second. Each of these samples is measured to an accuracy of 16 bits, storing the results in a 16-digit binary format.

Record a high-resolution track, on the other hand, and you’ll take a step up to 24 bits, with a sample taken as often as 192,000 times per second.

Digital audio data can be stored in a variety of sample rates, bit depths, encoding and compression formats – but no matter how it’s done, it is the DAC’s job to make sense of it all, translating it as accurately as possible from its binary format to return it as close to the original analogue recording as it can.

Why do I need a separate DAC?

Audioquest DragonFly Cobalt

Audioquest DragonFly Cobalt (Image credit: Audioquest)

While it’s true just about every piece of digital kit features a DAC, it’s just as true that not all DACs are created equal. For starters, they might not support all file data rates.

Poor converters can introduce unwanted noise during playback due to poorly designed circuitry, not to mention add extra distortion due to jitter. (Jitter is best defined as digital timing errors. The precise timing of a digital music stream is vital to high performance, and if that isn’t done properly - usually because of poorly designed digital-clock circuitry - performance suffers.)

Jitter problems can arise every time a digital signal has to travel around a circuit board – and it’s particularly troublesome when the signal is transferred between devices. In recent years we’ve seen the rise of the asynchronous DAC, which takes over timing duties from any computer it may be connected to for just this reason.

The digital clocks found in dedicated hi-fi DACs tend to be more accurate than those used in the average PC, so usually, the conversion process will be performed more faithfully.

The source material is all

Chord Hugo 2

Chord Hugo 2 (Image credit: Chord)

Of course, to get the most from a DAC you need to start out with good source material – don’t expect miracles if all you’re throwing at a converter is 128kbps MP3s. In fact, better decoding of such a compressed signal can make any sonic shortcomings more obvious.

You’ll hear optimum results with CD-quality content and above, which is best stored in FLAC, WAV or ALAC (Mac) lossless PCM formats, or alternatively DSD if you prefer.

What is DSD and PCM?

DSD, or Direct Stream Digital, is an alternative to PCM and was originally conceived for Super Audio CD (SACDs) – a format championed by Sony and Philips in the late ‘90s and into the ’00s.

It’s a much more niche format, differing from PCM by offering a bit depth of just one, but much higher sampling rates – commonly DSD64 at 2.8 MHz and DSD128 at 5.6 MHz.

The arguments as to which encoding system is better continue to rumble on. Suffice to say if you’re someone firmly settled in the DSD camp, it’s worth checking the DAC you’re considering supports it – most, but not all, do.

What type of DAC is right for you?

Astell & Kern AK USB-C Dual DAC Cable

Astell & Kern AK USB-C Dual DAC Cable (Image credit: Astell & Kern)

DACs come in all shapes and sizes and offer varying levels of input options and functionality, so you’ll need to think about how you want to use it, not to mention the budget you have set aside.

Compact USB DACs offer portability and convenience at a reasonable price. They vary from USB sticks (such as the Audioquest DragonFly Red) that connect to a laptop, to more modern USB-C cable DACs (like the Astell & Kern AK USB-C Dual DAC Cable above) that connect to a phone with that connection.

More often than not they use the power from your computer or phone, so there’s no need for an extra power source. They largely keep connections simple, with just a headphone socket and possibly a line-level output for hooking up to powered speakers or a hi-fi system.

Audiolab M-DAC+

Audiolab M-DAC+ (Image credit: Audiolab)

If you need more connectivity and are not concerned about taking your DAC around with you, a desktop USB unit might be more suitable. These are usually bigger and require their own power source, but often offer several additional digital or analogue audio inputs alongside a USB input for connecting to your computer. Some, like the iFi Zen DAC V2, can be either USB or mains powered.

Keep an eye out for a DAC with a headphone amp if you want to use headphones, as not all DACs offer this as an option – the Award-winning Chord Qutest, for instance, is a standalone DAC without any headphone features, designed to slip into a system between a digital source and amplifier.

Finally, there are the DACs that are born to work as part of a bigger home audio system. These will usually have even more inputs – particularly more niche sockets such as AES/EBU – and, potentially more features too. They'll support the full range of high-resolution music formats, for example, or offer Bluetooth connectivity for streaming wirelessly from your smartphone or tablet (which portable and desktop units tend to offer these days too).

Some will even come with volume control, so they can be used as a pre-amp too.

These can range from the sensible (the Audiolab M-DAC+, say) to the extravagant (the Chord DAVE) or, if money really is no object, the Nagra HD DAC/MPS.

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