Extron Electronics MLS 608 D Series User Guide - Manual (Page 38)

Line input building blocks
Extron building blocks for line level devices set the gain level for the specific device and
its operating line level. Bass and treble shelving filters are inserted into the filter block,
with gain level set to 0 dB. This allows for tone adjustment, if necessary, either via the
DSP Configurator software or by programming the gain parameters into a control system
and allowing the user to make adjustments. Light compression is added to the channel to
normalize diverse signal levels, with threshold set at -17 dBFS and a 2:1 compression ratio.
The compressor threshold is at target level so as not to greatly affect unity gain (at the
target level) through the system.
The table below shows different line level device categories, and their operating line level.
Gain compensation is based on the operating level and the gain required to bring the
signal up to the target level. When the target level is achieved at the input, maintaining
unity gain through the system will produce + 4 dBu at the output. Gain compensation for
line levels in dBV is calculated by first converting the source output level to dBu.
Source Type Operating Level Gain Compensation Target Level
Consumer Player -10 dBV +11.8 dB -17 dBFS (+4 dBu)
Computer Sound Card 0 dBV +1.8 dB -17 dBFS (+4 dBu)
Pro Level (balanced) + 4 dBu 0 dB -17 dBFS (+4 dBu)
Broadcast Level + 8 dBu -4 dB -17 dBFS (+4 dBu)
Line output building blocks
The output channel building block inserts an equalization curve into the output signal
chain of the DSP. A compressor is inserted on the output, set to a nominal level for speaker
protection. The output level is given a nominal setting from which you can make final
adjustments to suit the room.
Background
The equalization curves used for the output building blocks were generated by measuring
the sound power response of an array of nine (9) identical speakers mounted in a large
acoustically dead room. For testing, 400 samples were taken throughout the sound field
of the speaker array and averaged together, which provided the average sound power
response of the nine (9) ceiling speakers. This was repeated with the speaker array at
6 feet, 8 feet, and 12 feet spacings between speakers. The results were merged into a
single response curve for all three configurations, comprised of over 1200 samples (total
average).
NOTE: An array of four (4) Extron FF 120T and FF 220T speakers were used at 12 feet,
16 feet, and 20 feet spacings, since the Flat Field Technology ® provides more
consistent sound levels across the listening area than conventional coverage
patterns.
This total average curve was then inverted and loaded into a real time analyzer (RTA).
Calibrated pink noise was introduced into the Extron DSP and the output of the DSP
presented to the RTA. The RTA was put into A - B subtraction mode, with the total
average curve being subtracted from the real time pink noise. The resulting response
on the RTA was an electrical facsimile of the average acoustic response of the speakers.
Parametric filters were then employed on the DSP to flatten the response curve on the
RTA. Those filters were then saved into the building block for that speaker type.
MLS 608 D Series • Operation 32