Line Booster, Signal Refresher; Correcting Incorrect Sample Rates; Vari-Speed Application; Format Converter - Behringer ULTRAMATCH PRO SRC2496 User Manual

10
ULTRAMATCH PRO SRC2496
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/software—without 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
tape—usually only monitored briefly on the DAT recorder due to lack of time—
arrives at the customer's 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 ULTRAMATCH PRO 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 ULTRAMATCH PRO 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
ULTRAMATCH PRO 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 ULTRAMATCH PRO 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 ULTRAMATCH PRO 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 ULTRAMATCH PRO. 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 ULTRAMATCH PRO 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 ULTRAMATCH PRO 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.
There is no doubt that digital signal processing guarantees the lowest distortion
and noise values. However, up until now signal conversion, specifically sampling
rate conversion, had partially led to considerable distortion and interference:
If you tried to use traditional methods, the incoming data quantity would far
exceed any hardware capacity. If data was put into smaller pieces to avoid
storage problems, the necessary turnaround time would prevent any practical