PRO audio has been embracing Firewire and SPDIF for too long. SPDIF was really the only reason that we looked at Jitter in the first place. Like Firewire, SPDIF requires a moving oscillator to match the sending units internal Sample Rate. Sure USB has this mode as well used in many audio devices and is called Adaptive Mode. Anytime there is a moving clock to match the sending unit, this causes jitter in the conversion from data to what we call the audio stream to or from the DAC (Digital to Analog Converter) or ADC (Analog to Digital Converter).
With Asynchronous USB we can take that control back from the computer and instead use ultra low jitter fixed audio oscillators for the reference clocks and work the DAC & ADC from these resulting in a minimum of 100x better sound. Many companies making Firewire and SPDIF converters will make you think that the computer has to resample the data going out or that there is some inherent design flaw in this technology. These are all lies into keeping the flock moving forward to a new technology that kicks the pants off of what you are using now.
Why Fix Jitter?
Since the beginning of Digital Audio we have been trying to fix jitter. As engineers we have used secondary PLL, FIFO's, reclockers, upsamplers you name it. This has been the thorn in the side of every digital engineer.
With USB came a mode that is supported under all operating systems called Asynchronous USB. Unlike other USB DAC/ADC (Adaptive) the DAC/ADC actually controls the flow of data and operates all the internal I2S protocol and dac clock using a very low jitter Master Clock. No longer is it require to fix the jitter as there was very little from the start.
Adaptive mode USB on the other hand is required to change the clock every 1ms which in it self adds jitter to the system. The Master Clock in Adaptive systems that generates all the I2S signals is derived from a programable high jitter clock. All of these types of products usually use some sort of method to Fix Jitter, otherwise it would be too high to tolerate.
Streamlength Asynchronous USB Audio-What’s it all about?
Every USB DAC you have ever heard uses Adaptive Mode USB Audio. This means the computer controls the audio transfer rate, and the USB device has to follow along updating the Master Clock (MCLK) every one millisecond. The USB bus runs at 12MHz, which is unrelated to the audio sample rate of any digital audio format (i.e. 44.1K requires a MCLK = 11.2896MHz). Therefore Adaptive Mode USB DACs must derive the critical master audio clock by use of a complex Frequency Synthesizer. Since the computer is handling many tasks at once, the timing of the USB audio transfers has variations. This leads to jitter in the derived clock, which means you are not getting the maximum sonic potential available from computer-based audio.
Now, for the first time ever, Wavelength Audio has developed Asynchronous Mode USB Audio. This means the computer is controlled by the USB DAC. No longer is the tail wagging the dog. Instead, an ultra-low-jitter audio master clock located in the DAC controls the audio transfer rate from the computer. Jitter is reduced by a factor of greater than 100 times! What's more, this is accomplished using the standard USB drivers (Windows or MacIntosh) for easy plug-and-play installation. Now the convenience of computer-based audio is combined with the lowest possible jitter. This breakthrough technology from Wavelength Audio delivers the highest level of sonic performance and a new era in digital audio.