Synchronous and asynchronous are two buzz words manufacturers realize gets people's attention. We may not understand what they mean but we've figured out asynchronous is better than being synchronous. So a new class of DAC has been born, the Asynchronous DAC - only it's mostly a myth and a misleading one at that.
Here's the deal. When you connect a transport or CD player's digital output to a DAC's input, the DAC is in synchronous mode with the player. This means the player or transport is the master clock that runs the whole shooting match inside the DAC. That's standard on just about every input on your DAC, all of which are running in synchronous mode.
Over the last couple of years we've seen an influx of USB inputs on DACS, The first of these inputs were synchronous, meaning the computer was the master clock that ran the DAC - just like the example we cited of the player.
Since players, transports and certainly computers were never designed to be great, low jitter stable clock sources, if we had our druthers we'd rather not have them controlling the audio quality and timing of our DACS - and when we provide our own controlling clock, that's what's known as asynchronous.
Then a few pioneers like Genesis, PS Audio,Gordon Rankin and XMOS started introducing the world to asynchronous schemes that sounded better. Genesis was the first when Bob Stadtherr and I invented the Digital Lens in the mid 90's - an asynchronous source for anything plugged into it, followed by our PerfectWave Transport Memory Player - an asynchronous transport,then Gordon in his great Wavelength products and lately XMOS a chip manufacturer making it easier for DAC manufacturers to add asynchronous USB. Now, many DACS have asynchronous USB inputs, but that doesn't mean they are an asynchronous DAC.
To qualify as an asynchronous DAC, every input of the DAC (not just the USB) would be asynchronous - where the designer would throw away the source clock and rely only on the DAC'S internal clock. There are scarce few of these around.
Not to toot our horn but the PerfectWave Mark II is one of but a very small handful of true asynchronous DACS where every input is run through our Digital Lens and output with an independent asynchronous low jitter clock.
So the next time someone tells you they have an asynchronous DAC, you're now armed with the info you need to ask the right questions.