Digital to Analogue convertors, usually known as DACs, have played a vital role in high-quality music reproduction since the introduction of the Compact Disc. But as the CD dies out, DACs have grown in importance, as we all strive to get the best possible performance from our digitally stored music collections. Bowers & Wilkins Product Marketing Manager Mat Taylor gives his definitive guide.
From the nostalgia of the first LP bought to the latest download purchase, the flat pack CD towers to the portable hardrive backup, the smoothest eject mechanism to the cover flow finger swipe. All aspects of music consumption have drastically changed over the past decade.
With the rapid evolution of digital audio technology it is sometimes difficult to keep up, and sometimes even harder to leave behind the love of old formats and hardware. There is no doubt that a high quality music collection accessible anywhere is the holy grail of music convenience, but how can you ensure the ultimate listening experience, especially, when the music library is stored on a computer?
For many digital music users the computer’s output is routed to active speakers or a separate amplifier using an analogue connection. In this case, the process of changing the digitally stored data to an audible analogue signal is processed by the computer’s internal components and therefore performance limited. These components are known as Digital to Analogue Convertors (DACs).
Separate DAC systems are not new; it’s more than two decades ago that separate DAC components became available to the mass market. This allowed the audiophile consumer to tap into the digital audio signal path and achieve superior digital to analogue conversion compared to the source’s internal DAC components. Recently, we have seen an influx of dedicated DAC equipment to operate on the reproduction routine for digitally stored music libraries. Increasingly, USB plays a major roll here. Having a standard connection makes it possible to perform keyhole surgery, extracting 1s and 0’s from the heart of the computer. Once extracted it is possible to upscale and convert to analogue with less jitter and errors than ever before.
Clocking is very important with digital audio, to get the most accurate sound a master clock should be used for all digital components. Initially, a vast majority of DACs were ‘adaptive’ USB mode, which means that the clock is variable, typically changing the master clock frequency to match the average sampling frequency of the data it receives. As computer clocks may not perform consistently for a variety of reasons there is a risk of jitter with adaptive USB mode. USB standards allow for an “asynchronous” USB mode, here the DAC’s master clock isn’t synchronized to the clock in the computer. Instead, the DAC is controlled by a precise fixed clock and the frequency of data is managed using a buffer. Originally, these devices were less common as manufacturers would be required to development bespoke software for the available chipsets. Over time several companies have invested in this coding and are now licensing solutions to brands, hence we now see more affordable asynchronous DAC products available. Of benefit to asynchronous USB modes is the two-way communication between the computer and DAC. This allows the computer to follow instructions from the DAC after the audio has been sent. For example if the computer’s clock has become less accurate over time and as a result quickly fills up the buffer with too much information, an asynchronous DAC would tell the computer to slow down stabilizing the buffer and avoiding audio artifacts and dropouts.
Sampling rates have increased with newer DACs, we now see the availability of 384kHz (eight times 48kHz!), sampling previously restricted to rare ultra-high end equipment. The point here is that although CDs were sufficient to reproduce frequencies above the hearing range, we can now reproduce sound closer to nature providing the magic that contributes to the most realistic listening experience. The ability to support 32-bit resolution sees a theoretical signal to noise ratio (SNR) of about 194dB, CD players at 16-bit resolution would see a SNR of just short of 100dB. Noise in a 32-bit system is down to that of traditional analogue sources. However, we have to consider here the availability and capacity requirements of such a 32 bit/384kHz recording format. For the time we will have to be content with 24 bit/192KHz format.
Another important technicality of the DAC is the filter window; this is the component that shapes the audio. Advances in technology have now made it affordable for consumers to replicate the precision of a flawless system.
At a time of convergence the thought of a dedicated DAC separate will not appeal to all audiences. The market has responded to this in several ways: with a range of media servers implementing asynchronous DAC components; but also with the very special take on the asynchronous DAC found in the new Classé CP-800 pre-amplifier.
So, while the way we experience music may have changed over the years, for many people the goal of attaining the best possible sound has not. And new DAC technology is one of the most powerful weapons in the audiophile’s armory.