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4.5 Analog Microphone Preamplifiers
Although the primary purpose of the DI-PORT is signal conversion, some users, impressed
by the high quality of its microphone preamplifiers, will want to use it in conjunction with
an analog mixer. This is anything but a problemæthe Monitor Out sockets can be used
specifically for this purpose. All you have to do is adjust the Monitor knob located on the
front panel so that solely the input signal of the DI-PORT is routed via this circuit. Simply
connect the Monitor Out sockets to two inputs of your mixer. With this setup, you can
exploit the excellent audio qualities of the microphone preamplifier even when you’re not
using the device’s converters.
5. Background Information
5.1 Disadvantages of Conventional Audio Cards
Soundcards are developed primarily as universal expansions in order to turn a PC into a
gaming or multimedia system. Their audio interfaces are just one feature among many:
A soundcard also offers a synthesizer-type sound generator, a joystick connection and a
MIDI port. If you ignore the features that are irrelevant to musical applications and focus
solely on the audio section, you can of course in principle use a soundcard as an audio
interface. However, bear in mind that cheap soundcards have serious drawbacks which
pretty much preclude the use of these for any serious musical application. Due to their
typical lack of linearity and poor signal-to-noise ratio, the audio quality of cheap
converters is very shoddy. Plus, due to the layout of motherboards, which aren’t designed
specifically for hard disk recording, cards often have to contend with pick-up of stray
interference, which becomes audible in the form of humming, hissing or whistling noises
emitted by the computer.
Many soundcards are equipped with power amp ICs that drive small multimedia
loudspeakers that are connected to the card’s outputs. If dedicated line outputs are
unavailable, you’ll encounter all kinds of compatibility problems and have to use adapters,
which will also degrade audio quality. Finally, many soundcards aren’t full-duplex enabled,
which means they are unable to record and play back signals simultaneously. As you can
well imagine, this functionality is absolutely essential, for example, when you want to
record a vocalist singing along with previously recorded tracks. Otherwise, for the obvious
reasons, the vocalist will have a hard time singing in time with something he or she can’t
hear. Therefore, for your musical endeavors, you are well-advised to opt for a high-quality,
full-duplex enabled audio card that is free of the problems we just discussed. However,
bear in mind that even if the card is equipped with decent converters, it can never cure an
inherent ill: By design, converters and analog components are installed in the interior of
the computer’s housing, which means that they are exposed to the considerable
electromagnetic interference prevailing inside a computer casing as well as interference
transmitted via the data bus and power supply.
This is why you should choose an audio card equipped with a digital interface or a pure
digital I/O card that you can operate in combination with the DI-PORT. Its preamplifiers
and converters are not only much better than those of standard audio cards, they are also
housed in an shielded outboard chassis that protects components from interference. In
addition, the DI-PORT is equipped with high-quality microphone preamplifiers featuring
phantom power. Not a single audio card currently available on the market offers
comparable features despite the fact that phantom power is something you can’t do
without when you’re using capacitor microphones,.
5.2 What Will 24 Bits Do for You?
When an analog signal is digitized, the level of the analog signal is measured at specific
intervals and represented numerically. The 16 bits of the CD format allow a representation
of 2 to the power of 16, which translates to 65,536 individual or discrete increments. If the
level of the initial analog signal lies somewhere between the discrete values of two of
these steps, the converted signal will contain an error. The size of this error varies with
each sample and is perceived by your ears as a type of interference called quantization
noise. On the other hand, a digital word length of 24 bits allows signals to be represented
by more than 16 million steps, which yields a considerably more accurate digital
approximation of the signal and hence significantly less quantization noise.
Incidentally, the superior 24-bit quality of the DI-PORT is beneficial - some might call it
imperative - even if the final product of the recording is a 16-bit CD. How so? Because
when you're recording with a 16-bit converter, in many cases only 14 bits are actually
used to represent the signal. The other two bits are reserved as a kind of digital
headroom. If the signal is compressed in the course of processing, quantization noise
- initially soft - becomes significantly more perceptible. Finally, during digital post-
processing, rounding errors are generated in computation operations. These errors are
always apparent in the lowest bit. For these reasons, it's a good idea to work with 24 bits
and refrain from converting the signal down to the 16-bit CD format until you've executed
all processing operations in your recording system. In other words, conversion should
always be the final step. The great advantage here is that the potential of the CD format is
exploited fully, right down to the last bit. Your tracks thus end up with the best possible
dynamic response, definition and fidelity.
6. Block Diagram
Page 30
7. Technical Data
Page 31
MindPrint DI-PORT
