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ULTRAMATCH PRO SRC2496
4. TECHNICAL BACKGROUND
the signal has been processed with this technique. It is however
NOT a modification of the audio signal, but only of the emphasis
marker contained in the digital data stream.
So much for the theory. In practice, a lit EMPHASIS LED does not
necessarily show that the emphasis function has really been
applied. In several situations the emphasis bit was set during the
mastering and editing process due to defective hardware/
softwarewithout any treble boost applied. This error usually
remains undetected when the material is transferred, because
modern DAT recorders no longer have an emphasis indicator for
reasons of rationalization. When the master tapeusually only
monitored briefly on the DAT recorder due to lack of timearrives
at the customers end, it gives him a big surprise: The treble range
has been cut in the DAT recorder by more than 10 dB, which
cannot be undone and results in a dull sound that lacks brilliance
in the treble range. It is for this reason that we equipped the
ULTRAMATCHPRO both with an emphasis status LED and with
an additional switch for manual correction of the emphasis bit
setting.
3.5 Line booster, signal refresher
Longer cable lengths or the use of a digital patchbay lead to
deterioration of signal quality, which may result in a higher
noise floor or even connection failures. Using special input
circuitry your ULTRAMATCHPRO removes jitter, interference
and level loss, thus restoring the signal to perfect quality. As a
consequence, you can also use the SRC2496 to refresh the
signal over longer cable lengths or to restore attenuated and
distorted signals.
3.6 Correcting incorrect sample rates
The sample rate of any equipment is subject to fluctuation due
to temperature and ageing effects. Normally, an automatic locking
circuit ensures reliable operation even with varying or slightly
fluctuating clock signals. If such fluctuations exceed a certain
level, however, the receiving equipment cannot be synchronized
any longer to the clock rate supplied and therefore fails to function
properly.
Your ULTRAMATCH PRO is totally free from such restrictions,
as it works over the entire bandwidth from 31 to 100 kHz, rather
than only within a small range around the actual sampling rate.
The signal output by the SRC2496 is always synchronized correctly
to the value selected. Thus, you can use your ULTRAMATCHPRO
to rescue and work with sampling rates that have been modified
deliberately (vari-pitch function on sampling keyboards or CD
players) or fail to fall within the adjusted range due to rate
fluctuations.
3.7 Vari-speed application
There are several reasons for modifying the speed of a digital
playback, e.g. to change the pitch or synchronize the playback
to other equipment. In such cases, the ULTRAMATCHPRO can
track the sampling rate as it changes and then output the signal
with a fixed rate of 44.1 kHz (or any other selectable or wordclock-
defined value). Thus, it reliably removes sampling rate fluctuations,
which could otherwise make it impossible to process the digital
audio material any further in the digital domain.
+ At its digital input, the ULTRAMATCH PRO accepts
sampling rate fluctuations of up to ±12% from the
adjusted sampling rate, without producing any
distortion at its output. When things get worse, the
connection will not be interrupted, but temporary
drops in the signal quality (distortion) may occur.
3.8 Format converter
Digital data transfer is frequently affected by problems with
the format required. While some devices specifically need
S/PDIF signals on the input side, others can only output
AES/EBU. With the SRC2496 this problem is now history. The
input of your ULTRAMATCHPRO readily accepts any standard
used today. On the output side, you can select either AES/EBU
or S/PDIF, so that it is just a matter of one key press to realize the
successful transfer of your audio material.
3.9 Format interface
Many CD players have no coaxial but only an optical output.
Some DAT recorders, on the other hand, only have a coaxial
input. Digital interface cards for personal computers are usually
equipped either with optical or coaxial connectors. So, when you
try to transfer data from one unit to another you are likely to
encounter incompatibility problems, in that one unit has an optical
connector, while the other has a coaxial RCA connector.
Connection to professional equipment is difficult because of the
XLR connectors used there, or even impossible if it features
optical interfaces.
Such incompatibilities between inputs and outputs are definitely
a thing of the past with the ULTRAMATCHPRO. For example, if
the CD player only has an optical digital output, while the
DAT recorder is equipped with a coaxial RCA input, your
SRC2496 will easily eliminate the resulting connection problems
with its three inputs and outputs in all formats. Your
ULTRAMATCHPRO allows for interconnecting virtually all
equipment that is available on the market today!
3.10 Patchbay/splitter
The digital outputs of your ULTRAMATCH PRO can all be
operated at the same time. In this case, the input selector functions
as a kind of miniature patchbay determining which signal is sent
to the output. It is not necessary to switch-over the output,
because you can freely select on the down-stream devices
which signal to accept (example: recording active/inactive).
Therefore, the outputs of the ULTRAMATCH PRO carry the
identical signal all the time and are operative simultaneously.
The parallel operation of all three outputs enables you to use
your SRC2496 as a splitter, which is useful for copying material
to several DAT recorders. With some special types of equipment
in particular that does not allow for looping through the digital
data from the input to the output, this useful function makes it
possible to split up the signal.
4. TECHNICAL BACKGROUND
4.1 A short digression into digital sample rate
conversion
In the past, the conversion of various sample rates into a fixed
value necessitated a whole rack full of components and even
then had some disadvantages that could be measured as
increased noise, distortion or undesirable mirror frequencies
(high-frequency chirping). On the other hand, the sampling rate
converter chip installed in the ULTRAMATCHPRO converts in
real time and with 24-bit precision. Its processing is absolutely
inaudible and can only be identified with state-of-the-art,
extremely expensive measuring instruments.
The functional principle is difficult to comprehend, even for
professionals. That is why we are presenting you with an
equivalent model, which describes the processes taking place
in the processor in an easily understandable manner. The
processor carries out an oversampling at the input signal. Between
each sample, more samples are inserted, thereby significantly
increasing the number of sampling points by filling in the gaps.
Subsequently, the signal passes through a variable low-pass
filter, which ensures that the correct limit, below which no
problems with mirror frequencies (aliasing) occur, is observed.
Then, the number of sampling points is distributed in such a way
as to obtain the desired sampling rate at the output. This enormous
oversampling allows the SRC processor to achieve excellent
precision in the complete conversion range. Moreover, it also
simultaneously eliminates any jitter present in the input signal.