Knowledge Base

About Audio Devices

The appropriate audio device depends on your setup. Take the following rules of thumb into account:

• For room settings, use one omni-directional ceiling microphone.
• For meetings around a table, use one or more boundary layer table microphones.
• For usability research at a computer, use a microphone close to the test participant, for example a wireless microphone or boundary layer table microphone.
• For very good audio quality for more than one test participant, use a wireless microphone for each person.

Audio quality strongly depends on the room settings. An expensive audio device does not by itself guarantee good audio. If the devices are not placed correctly, or if the acoustics in the room is bad, audio quality will suffer.

Do not place the microphone cables in the vicinity of 110 V / 230 V electricity cables. If you, for example, put microphone cables in electrical conduits, the electricity can interfere with the audio.

Do not put microphones close to, for example, an air conditioner, a fan, or a computer.

Use curtains and other soft materials on the walls to reduce echo.

Dante Audio

Dante (Digital Audio Network Through Ethernet) is a combination of software, hardware, and network protocols that delivers uncompressed, multi-channel, low-latency digital audio over a standard Ethernet network. All inputs and outputs are carried as digital data running on lightweight, inexpensive Cat-5 or Cat-6 cabling.

In an analog set-up the physical connections are point-to-point and individual cables represent each channel. Copper cables are needed for each individual signal path. In Dante, the physical connecting point is irrelevant: as long as all the devices are connected to the same network, audio signals can be made available anywhere and everywhere. Patching and routing are configured in software and not over physical wired links.

Another major advantage of Dante audio is improved audio quality. It provides noise immunity and no audio quality degradation with long cable runs.

Preamplifiers

The signal from a microphone is of low voltage (mV). This signal needs to be amplified prior to further processing, like mixing or recording. This is done with a preamplifier. The strength of the signal that is amplified this way is called line-level.

The unamplified signal is very sensitive to noise. Therefore, the preamplifier should be positioned as close to the microphone as possible.

Balanced Cables

In professional audio systems, a balanced line or balanced signal pair is a transmission line consisting of two conductors of the same type. Both lines have equal impedances along their lengths and equal impedances to ground and to other circuits. Both lines are twisted together and then wrapped with a third conductor (foil or braid) that acts as a shield. Common balanced cables are cables with XLR connectors. Balanced cables are the opposite of unbalanced cables. A coaxial cable is an example of an unbalanced cable.

The main advantage of the use of balanced lines is good rejection of external noise. Because the signal between the microphones and preamplifier is most sensitive to noise, it is most important to use balanced lines there.

Phantom Power

Phantom power is a method to supply condenser microphones with power through microphone cables. Condenser microphones give better audio quality than other types of microphones, but they are more sensitive to noise. Preamplifiers and mixers can often supply microphones with phantom power.

Gain

The gain of a preamplifier is the degree to which the amplifier magnifies the low-level input signal compared to its output signal. It is the ratio of the output voltage divided by the input voltage and is expressed in decibels (dB). The formula to calculate gain is 20 x Log (Voltage output / Voltage input). A gain of 6 dB doubles the voltage 2 times and a gain of 20 dB gives a 10 fold increase in the signal.

Source: Viso 12 Setup Manual - About Audio Devices, Noldus Information Technology