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 hardrive like the Iomega Mini-Max at least 500gigs
Blue Tooth mouse and keyboard
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
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: