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 DACS (Adaptive) the DAC 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.

Computer Audio 101

A typical setup for a USB DAC system is shown above. We have two Firewire disks for our library (one is for backup). We use Firewire over USB drives because we don't want to overload the USB link. The output of the DAC is fed to a preamplifier or integrated amplifier and then to the amp and speakers. There are several suggestions for full remote control located on the setup pages for Macintosh and Windows.

We set the playback software (i.e iTunes, J River etc.) to read your CD's and write the error free tracks to the Firewire disks. The playback software then has all the information including the CD titles, names of songs, plus the actual tracks on the disks for use in playing these back.

Most playback software also allows you to watch downloaded movies as well as stream music from internet radio stations.

To make sure we don't loose our Library of ripped CD's on our Firewire disk, we make a backup and put that on a different drive. There is some really good Sync software as well as back up programs available to make sure you never loose any of the material. It will be saved off on the backup disk exactly as it is on the main disk. I basically sync the two drives after I rip allot of CD's to my main library. Then I turn the back up drive off, thereby evading some kind of power or other issue.

The computer does need to have internet access to get song names and such. But it does not need a specified email address of any kind.

You can use computers such as the Apple MAC Mini as a complete entertainment system with DVD, DVR/Cable (Elgato EyeTV), music, radio and all sorts of stuff like this:

Basically use the DVI connector (HDMI convertor can be used if your TV does not support DVI) out of the Mac Mini into a large screen LCD or Plasma TV or Monitor. This becomes your monitor and you can see DVD's and Cable output (via Elgato) as well as iTunes and other applications on the large screen. This places your Mac Mini as the central place for all your music, video's and other entertainment options.

I always tell all my customers that buying all that extra stuff for home theater is a waste of money. Given any budget, the quality of a two channel system is always going to be higher than a home theater system because there are fewer things to buy, leaving you with more money to put towards less items. There is a huge trend out there for people to buy home theater receivers for a stereo system because they want to be able to have the potential of “upgrading” to a home theater in the future. The reality is that no one wants to wire for rear speakers and you just spent a chunk of money on a component which you will never use as it was intended.

Instead I say go two channel audio and video for the best results. With a computer in the mix, you can build yourself a high quality two channel home theater system with iTunes access to music, movies, and even the ability to watch and record live cable TV!

Equipment required:
Apple Mac Mini
An external Firewire Hard Drive for the main library and also a back up drive, so two of the same size.
Blue Tooth mouse and keyboard
Depending on the MAC, DVI to HDMI cable convertor (if required) DVI monitor or DVI capable TV will result in the best resolution.
Elgato eyeTV cable TV to USB 2.0 unit for DVR and Cable hookup
Apple Time Capsule for wireless internet and media backup, not required if you have a back up hard drive.

When done you will be able to watch movies, play audio, stream internet radio and video, record cable and just about anything else you can think of through this system.

The Apple Time Capsule can be used to automatically back up all of your movies and music wirelessly.

You can use Front Row ( software program that is included with your Mac Mini) to control the whole operation via remote control (which is also included in the Mac Mini box) Other
remote options are available on the Macintosh page: