Lab.gruppen PLM Series Operation Manual - Appendix 11
PLM Series Operation Manual 57
Term
Description
10/100base-T
10Base-T and 100Base-T are IT industry-speak for two different standards of Ethernet network. In broad terms, the older 10Base-T
operates at 10Mbps but has now been largely supplanted by the 100Mbps 100Base-T.
Access Point
See Wireless Access Point.
AEs/EbU
AES/EBU is the abbreviated term generally used to refer to the internationally agreed standard for transmitting two channels of digital
audio between items of equipment. The AES/EBU standard caters for audio at up to 24-bit and various sample rates. It is also allows for
various items of Control and User data to be included in the bitstream. XLR3 connectors are used for interconnection, but special cabling
techniques must be observed.
Analog
Conventional “non-digital” audio is termed analog audio. Conventional power amplifiers are inherently analog devices as far as power
amplification is concerned, though the PLM can accept digital as well as analog inputs.
Attack time
How fast a dynamics control circuit - such as a limiter or compressor - reacts to an increase in input signal level (above the threshold) is
termed its Attack Time. Attack Time may be fixed, program-dependent or adjustable by the user. The various limiting circuits in the PLM
include examples of all three.
Auto-sensing
The Ethernet ports on the PLM automatically determine the base speed of the network they are connected to (10Base-T or 100Base-T) and
configure themselves appropriately. This is termed auto-sensing.
Auto-uplink
The Ethernet ports on the PLM are able to operate with either straight or crossed network cables. This ability to connect correctly with
either type is termed auto-uplinking.
Auxiliary output
Some of the configurations possible in the Dolby Lake processing system Modules result in a single audio processing channel being created
in addition to a crossover. This is termed an Auxiliary output.
backbone
Large Ethernet networks are often implemented with a very high speed “trunk” part of the network topology feeding main switches, which
in turn support smaller, lower-speed local networks. The term backbone is used to describe such a trunk.
balanced
Various types of electrical signal are transmitted between equipment in a balanced configuration. This requires three conductors, which
are generally termed Hot (+), Cold (-) and Screen. Balanced transmission of analog audio is preferable to unbalanced, and is mandatory for
AES/EBU digital audio and RS485 control data. The analog audio inputs on the PLM are balanced.
bandwidth
The bandwidth of a signal channel or interconnection is the range of frequencies it is able to handle. The term can be applied to both audio
channels and Ethernet networks.
bessel (filter)
There are many different designs of audio filters, such as are used in crossover networks for example. They tend to differ primarily in the
flatness of frequency reponse in the pass-band and in the phase relationship of signals at different frequencies. The Dolby Lake processing
system offers a choice of traditional filters (Infinite Impulse Response) of which Bessel is an example.
block
The PLM’s front panel display is divided into eight areas termed in this manual as blocks. Each block is adjacent to one of the soft
buttons.
butterworth (filter)
See Bessel.
Cat-5e/Cat-6, etc.
Designations of industry-standard cables suitable for Ethernet networks using four twisted pairs of conductors. Often referred to as UTP
cable (Unscreened Twisted Pair). Cat-5 has generally been replaced by Cat-5e (e = ‘enhanced’). Either Cat-5e or Cat-6 cable are suitable
for networking the PLM.
Chain
An Ethernet network comprising several PLMs (or other devices) interconnected using the Secondary connectors to daisy-chain the units
together is an example of a network with a chain topology.
Channel
The four outputs of the PLM and their associated processing sections are termed Channels. On the front panel, the four right-hand soft
buttons and display blocks relate to the four channels.
Clip/Clipping
If the level of an audio signal is so great it reaches the limit that can be handled by a particular processing stage, clipping is said to occur.
In an analog stage, this will be when the peak signal level equals the internal supply voltage of the stage, and distortion will be heard.
Clipping can also occur in digital processing, when a condition termed ‘data overflow’ results. This will be heard as a very unpleasant form
of extreme distortion. Careful adjustment of signal levels and an understanding of the PLM’s gain structure will avoid clipping.
Clock
Digital audio is produced by sampling analog audio at a known, fixed rate, controlled by some form of master clock. Problems can occur
when interconnecting two pieces of digital audio equipment if their internal master clocks are not synchronized. Various techniques may
be employed to ensure that this is the case.
CPL
Short for Current Peak Limiter, a Lab.gruppen protection technique which ensures that the amplifier’s output transistors can never attempt
to deliver more than their rated current.
Crossed network
cable
An Ethernet cable in which four of the eight conductors (pins 1, 2, 5 & 6) are not wired pin-to-pin. Such a cable is required in conventional IT
networks to connect two PCs together without using a hub or switch. The auto-uplink feature of the PLM’s Ethernet ports allows crossed
cables to be used if wished. See also Straight network cable.
Crossover
An audio processor which divides the audio signal into two or more bands of frequencies, each of which is then amplified independently
and routed to a loudspeaker of the appropriate type for those frequencies.
Daisy chain
Connecting the inputs of a series of audio equipment by wiring from the first piece of equipment to the second, then from that to the third
and so on is termed daisy-chaining. On the PLM, daisy-chaining is simple as all inputs – analog, AES/EBU digital and Ethernet – are provided
with Link connectors.
Dante
A new-generation audio data protocol developed by Audinate
®
Pty Ltd, allowing multichannel high-resolution digital audio plus control data
to be transmitted via standard IT-industry networks using TCP/IP data packeting. The Dolby Lake processing system integrated within the
PLM includes a Dante interface, which can provide the audio inputs to the PLM.
db
Abbreviation for decibel, standard unit used to describe the ratio between two different voltage or power levels. Hence parameters of gain
and attenuation are expressed in positive or negative dB’s respectively; e.g., a gain of 6 dB (+6 dB) means the signal voltage is doubled.
Note that a dB is not an expression of an absolute signal level – see dBu.
db/octave
The slope of an audio filter (such as implemented in crossovers) is expressed in dBs per octave, generally written as dB/oct. The higher the
number, the steeper the slope, and thus a lesser amount of the unwanted frequencies.