7
About the Clock / Jitter Control
Jitter control devices (and inputs on most DACs) normally reclock the input
signal in attempt to lessen the jitter of that incoming signal. The DAC IV
does no such re-clocking. We actually pay no attention to the clock on the
input signal. All internal clocks are generated by an extremely accurate plug-
in clock. Since the input clock is no longer related to the clock of the DAC
IV, an intelligent ½ second buffer is used to maintain data synchronization.
A clock header is a part of the DAC IV that will allow even more accurate
clocks to be installed as an upgrade as they become available. Clock jitter
seems to be the single biggest contributor to digital harshness. MSB clocks
are the lowest jitter audio clocks in the world. The DAC IV plus models
are supplied with the Femto 140 Clock with about 140 femtoseconds of
jitter. The Galaxy Femtosecond Clock is a great upgrade and offers about
77 picoseconds of jitter.
Custom Software and Temporary Filters
A custom digital filter will allow you to tailor the sound of your Platinum.
Any form of custom FIR filter may be loaded into the MSB Digital Filter.
You may select a custom filter from our library, you may have MSB design
a filter to your specifications or you may send MSB a list of Fir Filter
coefficients that we can format into a CD loadable file for you. You cannot
permanently damage your DAC by loading a Temporary Custom Filter, it is
only active until you power down the Platinum. Contact MSB Technology
for details on custom filters.
Step One, Verify Your Equipment Compatibility
- To successfully load your
custom filter you must have your Platinum connected to a transport that
will not change the Data. Almost all older CD players are acceptable,
however there are some important exceptions. Upsampling CD transports
will not work. The Upsampling drives are fine for playing audio after the
upload however. DVD players should work fine when they are configured
in a mode that does not affect the Data such as CD pass-through mode.
The iPod is an excellent way to play this file if you have the iLink upgrade.
the adding next sample. This repeated roundoff results in a
similar problem to the cascaded 2x filter approach, muddy
sound. MSBs digital filter uses bit perfect accumulation in an
80 bit accumulator completely eliminating these debilitating
roundoff errors. Only as the last step do we carefully convert
the audio to the 24 or 26 bits our DACs require. The high
sampling rate of the output allows us to include advanced
ultrasonic dither and noise shaping techniques in this step
to achieve greater than 24 bit effective resolution.
Through extensive listening tests we have found that the
choice of filter coefficients has a great impact on the tone of
the music. We have found that steep, phase perfect “Brick
Wall” filters tend to sound the most neutral but are also the
most difficult to implement without problems. Improvements
we have made in our digital filter, with its single stage design
and 80 bit computation, allow us to use very steep filters
with no compromises.
Custom Filter Options
We recognize that different people often have very different
taste in their music. For those who do not like the standard
choice of filter, or require a different filter response, we
have provided a very easy method for customizing your
MSB Digital Filter. By playing a standard CD containing a
custom filter algorithm you can temporarily change the filter
inside your Digital Filter. This CD filter loading allows you
to load almost any FIR filter quickly and easily. You may
also upgrade your MSB Digital Filter with the latest custom
software just by playing a special Firmware Upgrade CD.
The timing of the DACs conversion clock also has a large
impact on sound quality. Any periodic frequency change
or “jitter” causes a loss of focus in the reproduced audio.
The high power and large memory space of the SHARC
DSP we use allows us to offer a unique Ultra Clock to your
MSB Digital Filter. The Ultra Clock adds two ultra precision,
ultra low jitter TCXO oscillators and custom clock handling
circuitry to your board. This custom circuitry allows us to
do much more than simply reclock the data, as other jitter
reduction boxes do, but completely replace the incoming
clock!
Most jitter reduction schemes rely on Phase Locked
Loops or Asynchronous Sample Rate Converters. The
Phase Locked Loop is able to reduce jitter to a significant
degree but not eliminate it because the output clock must
be related to the input clock. The Asynchronous Sample
Rate Converter, which completely replaces the data and
clock, seems ideal until you realize that the complex
computation involved harms the data by permanently
imbedding a portion of the clock jitter into the data. Sample
Rate conversion is also detrimental to the sound due to the
complex and sub optimal digital filters involved, which must
change their filter response to track minute changes in the
input to output clock ratio.
The Ultra Clock sidesteps both of these problems by storing
the incoming data in an extremely large buffer (1/2 second
of audio.) The on-board clock then reads out the data
without jitter. The on-board clocks are totally independent
from the input clock so that no jitter is transferred to the
output. True absolute digital silences such as a track skips
are selectively shortened or lengthened by the DSP to
keep the buffer synchronized. This process is carried out
seamlessly by the DSP to assure that all compatible sample
rates have their clocks properly replaced. Compatible
sample rates are 44.1 kHz, 48 kHz, 96 kHz, 176.4 kHz,
192 kHz, 352.8 kHz, and 384 kHz. Other sample rates
automatically use the recovered clock from the transport
without user intervention. The large delay caused by the
buffer with 48 kHz sample rate audio from a DVD movie
may cause the audio to be unsynchronized. You can turn
this feature off with the remote.
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Summary of Contents for DAC IV plus
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