The pundits are quick to point out that the Greeks could have invented sound recording. How cool would that have been? We could hear scratchy records of Aristotle teaching or a bootleg of the premiere of The Bacchae. We would know how Greek music sounded, instead of having to make a bunch of wild, if educated, guesses.
But they didn’t so we don’t. It took Thomas Edison to cook up a practical technique for recording sound. Even if the Greeks possessed the necessary technology, they didn’t make the imaginative leap. Edison had a knack for such leaps.
The leap: sound isn’t so much a concrete thing as it is a process, patterns of alternating compression and decompression waves in a conductive medium such as the air. You can’t just copy sound waves, the way you can make a drawing or sketch of something visual or by reading and writing text. If you want to record sound, first you have to change it into something else. Then that something else serves as your persistent copy until you turn it back into sound again.
Edison’s solution was simple and brilliant: sound waves can make a thin diaphragm vibrate. That vibration can be captured by a variety of methods, in this case by attaching a slender needle to the diaphragm and then tracing the needle’s impressions on a medium that is pliable enough to take the pattern, but durable enough to allow retracing without obliterating the original. Edison started out with tinfoil, but before long he had settled on wax. The needle was guided horizontally over a hollow wax-covered cylinder, where it carved out a long, unbroken scratch.
It was a wholly mechanical process, plagued by friction and resistance and capable of capturing only a narrow slice of the sound spectrum. It’s a real tribute to the brain’s ability to fill in missing information that we can extrapolate enough to figure out what we’re actually hearing, even if in most cases the voices and instruments are stripped of most of their distinguishing characteristics.
Lee DeForest’s newfangled vacuum tube allowed for a dramatic easing of resistance and friction, given that the vibrating diaphragm could now induce a fluctuation in an electric current, capturing a dramatically wider frequency range. But ultimately the storage medium of choice remained that one long scratch. Eventually the scratch got a lot narrower as vinyl and LPs replaced the old shellac 78s. An alternate medium—patterns of magnetism that mimicked the fluctuating electric current—became the technique of choice for making the original recording. But most people still had lots of those long scratches at home, scratches that spiraled in from the outside to inside of a flat disc. The scratches were traced out by a stick with a needle on the end; the needle was suspended in a magnet; as the needle wiggled down the scratch the magnet gave off fluctuating electric current. That tiny bit of current was amplified enough to make bigger diaphragms (speakers) vibrate, and there you were.
As a result, that stick-needle-magnet combo was the critical item in a sound system. No matter how powerful the amplifier or the majesty of the speakers, everything depended on the quality of those minuscule fluctuations emitted by the needle as it scraped its way down the scratch. Garbage in, garbage out, as they say. So cartridges and turntables were big-ticket items for audiophiles, and for those folk who still pray to the gods of vinyl LPs and analog sound reproduction, cartridges and turntables retain an unfaded cachet.
But for most of us a sea-change took place during the 1980s when the old Edisonian paradigm was finally retired. Advances in computer technology made it possible to sample a sound—essentially to measure frequency and amplitude at very brief intervals, so brief that the sound wave could be reconstructed from those measurements. The stream of numbers could be stored by any means available to computer technology—on floppy discs, on hard drives, on data tape—but optical advances encouraged the development of the compact disc, which stores the data as microscopic pits etched into a spinning platter.
Nowadays, to “play” a sound recording means to initiate a stream of binary digits that must be converted into fluctuations of electric current that are subsequently amplified then used to elicit vibrations in speaker diaphragms. In other words, the last part of the playback equation—current to amplification to speaker—has remained unchanged since the 1920s.
The stick and needle and floating magnet are out of the picture. In their place we find the all-important digital to analog converter, or DAC for short. The DAC is to a digital audio system what the cartridge and turntable are to an LP analog system. Digits go in one end, and a fluctuating analog current comes out the other end. So, like the turntable and cartridge of yore, the DAC calls the shots in a sound system. Nothing can make up for a poor DAC.
And DACs aren’t brain-dead simple gizmos. They must decode the binary data stream accurately, and that’s no small task. For one thing, consider how precise the timing must be: a digital audio stream is usually streaking by at 44,100 samples per second or more, and if the timing clock isn’t ticking just right, the DAC might start mangling some of those samples—a phenomenon called jitter. DACs must perform plenty of error correction and do everything they can to keep jitter down to a minimum.
And once the DAC has taken care of deciphering the binary data stream, it must then produce the high-class analog current that feeds into the amplifier. If that analog current is sonically compromised, neither the amplifier nor speakers can do anything about it.
Amazingly enough, perfectly serviceable DACs are available on single silicon chips and are ubiquitous throughout today’s world. Any device you have that produces sound through digital means contains a DAC. Televisions, CD players, DVD players, wristwatches, cell phones, mp3 players, computers, tablets…they all contain audio DACs. Without a DAC, those devices would be mute.
But there are DACs and there are DACs. The two-cent chip that produces your morning alarm clock beep is designed to handle only the simplest of tasks. The DAC in an iPod or iPhone is far more sophisticated, although it isn’t all that toney. The actual analog signal produced by an iPod is mediocre, although most folks aren’t aware of that given that they’re hearing the sound through crummy earbuds.
For high-end audio, only a dedicated DAC will do, a separate device that is designed specifically for the purpose of taking in a binary data stream and turning that into as pristine and elegant an analog signal as possible. Audiophile-quality DACs don’t come cheap but a fine DAC can transform a stereo system beyond almost all recognition. Mediocre CD players can be turned into great ones, as the CD player is restricted to acting as a transport only, while the DAC does all the heavy sonic lifting. And an external DAC is by far the best way to extract ultra high-quality sound from a computer that is streaming digital data.
Slowly but surely I have come to understand the critical role a DAC plays in digital audio. As I moved my CD collection onto my home computer, I initially allowed the computer’s built-in DAC to take care of the conversion, plugging the computer’s ‘audio out’ into my home amplifier. The resultant sound was marred by all of the electronic mosh that goes whirring around inside a computer. And computers have very basic DACs, nothing fancy. A lot of audio potential was going to waste.
Eventually I learned to restrict my computer to managing the digital data only, connecting my computer via an optical TOSLINK cable to a home-theater amplifier. That was a big improvement, but I was being held back by the performance of the home-theater amplifier and its humdrum DAC and amplifier stages. So then I popped for a full-scale professional DAC, connected to my computer via USB. Now I was cooking.
Recently I made another step upwards by acquiring a highly-regarded audiophile DAC, the Bryston BDA-1, together with a bridge device that ensures a jitter-free data stream from the computer’s USB port. It’s the modern-day equivalent of replacing my old tone arm and cartridge with much higher-quality gear, and it has had a dramatic impact on my system’s sound quality.
Fortunately, very good DACs are available at only a fraction of the price of the Bryston. Nonetheless, you get what you pay for; high-end audio isn’t all snake oil, despite some of the carping you might hear. And once you’ve experienced what’s actually possible with digital audio, past iPods with earbuds or pounding boomboxes or thumpy computer speakers, you realize just how close we have come to that elusive, and no doubt unobtainable, goal of perfect sound reproduction.
There’s a good reason why external DACs have become such hot items in today’s high-end audio market, and why so many audio companies, including the most august in the business, have been bringing out DACs at every price range. Audiophiles have come to realize the DAC’s critical role in digital audio; it is low-grade DAC performance that is largely responsible for the brickbats so often tossed at digital audio, to the effect that it’s lifeless and harsh and grainy and metallic. Digital audio need not suffer from any of those shortcomings, but just as you can’t get much sound out of an LP via a cheapjack record player, you can’t extract the full potential of a digital audio stream without a good DAC. Digital-to-analog converters are the turntable-and-cartridges of the digital era, and they just keep getting better all the time. Trickle-down is doing its thing, and so modestly-priced DACs today perform like the high-end models of a decade ago. And with computer-stored digital audio rendering CDs and DVDs obsolete, quality digital conversion has become all the more important for those who find value in fine audio.