LA Audio MPX10 User manual

MULTI PROCESSOR
OPERATION MANUAL

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Version - V1 April 2000

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CONTENTS
Page
1. Introduction 3
2. Installation 4
2.1 Inspection and un-packing 4
2.2 Operating environment 4
2.3 CE standards 4
2.4 Power requirements 4
2.5 Signal levels 5
2.6 External connections 6
3. Warranty 9
4. Description of controls 10-15
4.1 Input section 10
4.2 Noise Reduction and Compressor section 11
4.3 Equaliser section 13
4.4 Output section
5. Applications 16-21
5.1 Input 16
5.2 Compressor 16
5.3 Expander 18
5.4 Equaliser 18
5.5 Output 20
6. Circuit description 21
6.1 Inputs 22
6.2 Expander and Compressor 22
6.3 Output 23
7. Specifications 24

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1.0 INTRODUCTION
The MPX10 is a single channel processor designed for one step
processing of vocal or solo instruments where the highest quality signal
path is required. The MPX10 combines a Mic/Line preamplifier with DI
input, Noise Reduction, 4 mode Auto Compressor and Equaliser in a
compact 1U case.
The MPX10 is an ideal front end for direct to tape or hard disk recorders
and as a superior analogue input stage for digital work stations. The MPX10
is equally at home in sound reinforcement applications where it can provide
feedback suppression, vocal levelling and comprehensive tone shaping.
Features include -
•Balanced Line and Microphone inputs (with +48V phantom power)
•High impedance (0.5M) DI input
•High and low pass filtering
•Downward expander Noise Reduction
•Auto Compressor with variable Threshold, Ratio and Gain
•In-built De-ess function
•HF and LF shelving EQ
•2 parametric mid range sections with Gain, Frequency and Q controls
•Output level adjust
•Gain Reduction and Output metering
•Ground compensated outputs at +4dBu and -10dBV
•Input and output break jacks for the Input, Compressor, EQ and output
sections
This last feature allows the user to re-configure the MPX10's signal path
such as putting the EQ before the Compressor. It also means that the
MPX10 can be used as 4 separate signal processors -
•High quality, low noise Mic, Line, DI preamplifier
•Downward expander and auto Attack/Release compressor
•4 band Equaliser
•Variable gain line driver with level metering

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2.0 INSTALLATION
IMPORTANT: PLEASE READ THIS SECTION BEFORE USING THE
MPX10
2.1 INSPECTION AND UNPACKING
The MPX10 has been carefully packed at our factory in a carton designed
to withstand handling in transit. Should the unit appear to have been
damaged in transit notify your dealer immediately and do not discard any of
the packing. The carton should contain -
•The MPX10 unit
•Power cord
•Operator Manual (this book)
2.2 OPERATING ENVIRONMENT
The MPX10 is designed to operate between 0 and 50°C (32-122°F) with
relative humidity no more than 80%. Should the unit be installed in an
equipment rack, ensure that the ambient temperature conforms to these
levels.
2.3 CE STANDARDS AND THE LOW VOLTAGE DIRECTIVE (LVD)
The MPX10 has been designed to meet the latest Electromagnetic
Compatibility (EMC) regulations. However we recommend you do not
operate the unit close to strong emitters of electromagnetic radiation such
as power transformers, motors, mobile telephones or radio transmitters.
The unit should only be connected to a power supply of the type described
in 2.4 POWER REQUIREMENTS or as marked on the unit. The unit must
be earthed for safe operation. Disconnect the mains supply before
removing any cover.
2.4 POWER REQUIREMENTS
There is a mains fuse located inside the unit which is accessed by
removing the cover. This fuse is for protection against unit faults and as
such will not normally need replacing. If you think you have a power related
problem please refer to your dealer.
The voltage and fuse rating have been factory set for -
230V 50mA UK and Europe
220V 100mA Republic of Korea

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110V 100mA North America
•The correct voltage and fuse rating is indicated on the
rear panel.
•Please check that your unit is correctly rated for the
voltage of the country of operation.
If the fuse requires changing at any time please ensure the correct fuse is
fitted. An incorrect fuse could cause damage to the unit and may constitute
a fire hazard.
If you carry your MPX10 from one country to another it is very important to
ensure the voltage is compatible.
For your information the unit can be internally rewired for use in 230V, or
110-125V countries - contact your dealer for information. A special 100V
version is available for Japan and a 220V version for Republic of Korea.
The mains lead connections to the appliance are coloured in accordance
with the following code:
Green-and-Yellow Earth
Blue Neutral
Brown Live
•WARNING: THIS APPLIANCE MUST BE EARTHED
2.5 SIGNAL LEVELS
For input level ranges see GAIN control in the Description of Controls
section.
The MPX10 outputs both -10dBV and +4dBu operating levels without the
need for level switching.
++ IMPORTANT NOTE: the XLRs are set for +4dBu and the TRS jacks
for -10dBV operating levels. Use the appropriate connector/level to
interface between your equipment and the MPX10.
The OUTPUT control on the MPX10 allows -20dB to +20dB of level
adjustment which should allow the MPX10 to interface to most equipment
types.
Signals in excess of +20dB will cause the unit to distort.
2.6 EXTERNAL CONNECTIONS

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INPUT SECTION:
MICROPHONE XLR Pin 1 Screen (Signal
ground) Pin 2 Hot (+ve)
Pin 3 Cold (-ve)
This is a low impedance (1.2k), low level input designed to give the
correct loading and sensitivity for dynamic type microphones. Plugging line
sources into this input may load the connected equipment and may result
in the loss of signal level, frequency range and increased distortion.
Pin 1 = ScreenPin 2 = Hot (+)
Pin 3 = Cold (-)
PUSH
Microphone Input XLR connections (view of connector on MLX2)
LINE TRS Tip Hot (signal +)
Ring Cold (signal -)
SleeveScreen (signal ground)
Sleeve
Screen Ring Cold(-) Tip Hot(+)
Fig 2.6.3: Line Input and -10dBV Output connections
The 20k input impedance of the LINE input is suitable for most types of
equipment.
For un-balanced operation join Ring and Sleeve on your connecting cable.
Plugging a mono jack lead into the LINE input will effectively un-balance the
signal connection.
DI jack Tip Hot (signal +)
SleeveScreen (signal ground)

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Sleeve
Screen Tip Hot(+)
Fig 2.6.4: DI Input connections
This a high impedance (0.5M) input primarily intended for connecting
directly to electric guitars.
OUTPUT jack Tip Hot (signal +)
SleeveScreen (signal ground)
This connector provides an unbalanced line level output from the
Mic/Line/DI preamplifier. Plugging a jack into this connector does not effect
the signal path through the MPX10. Source impedance is 100 which is
suitable for driving loads of 1k and greater.

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COMPRESSOR SECTION
INPUT jack Tip Hot (signal +)
SleeveScreen (signal ground)
This is the input to the Compressor section and is normally connected to
the 'output' of the Mic/Line/DI preamplifier. Plugging a jack into this
connector breaks the signal path and the Tip of the inserted jack becomes
the input to the compressor (Half-Normalled). All the 'Input' and 'Output'
connectors between each of the processing sections on the MPX10 work
in this way.
'Input' is unbalanced, however the connector is wired in such a way as to
be compatible with un-balanced (mono) and balanced (stereo/TRS) jacks.
SIDECHAIN jack Tip Return
Ring Send
SleeveScreen (signal ground)
Sleeve
Screen Ring Send Tip Return
Plugging into the MPX10's side chain automatically breaks the signal path
to the side chain circuitry. This path must be completed by the external
connected equipment.
The side chain in-out signal path affects both the Compressor and the
Expander response.
Commonly used to insert an equaliser into the sidechain to produce
frequency conscious compression such as de-essing.
Because each section of the MPX10 has Input and Output break jacks it is
possible to plug the EQ of the MPX10 into the Compressor sidechain to
allow more advanced Frequency Conscious Compression.
LINK jack Tip Control voltage
SleeveScreen (Control voltage
ground)
Link provides a means of joining the sidechain detectors of two MPX10s for
stereo operation. To ensure accurate stereo tracking the NR and
Compressor controls on both MPX10s should be set the same. Linking and
setting-up MPX10s in this way also ensures that signals from either MPX10
cause compression.
Please note that the Link output is a DC control voltage
and should not be connected into any audio signal path.

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OUTPUT jack Tip Hot (signal +)
SleeveScreen (signal ground)
An unbalanced output from the Compressor section.

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EQUALISER SECTION
INPUT jack Tip Hot (signal +)
SleeveScreen (signal ground)
Unbalanced input to the EQ section. Half-Normalled to the output of the
Compressor section
OUTPUT jack Tip Hot (signal +)
SleeveScreen (signal ground)
Unbalanced output from the EQ section.
OUTPUT SECTION
INPUT jack Tip Hot (signal +)
SleeveScreen (signal ground)
Unbalanced input to the Output section. Half-Normalled to the output of the
EQ section.
+4dBu XLR Pin 1 Screen (Signal ground)
Pin 2 Hot (+ve)
Pin 3 Cold (-ve)
For un-balanced operation join Pins 1 and 3 on your connecting cable.
-10dBV TRS Tip Hot (signal +)
Ring Cold (signal -)
SleeveScreen (signal ground)
For un-balanced operation join Ring and Sleeve on your connecting cable.

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3.0 WARRANTY
Your LA Audio MPX10 has been manufactured to a high standard using
quality components. If correctly installed and operated the unit should give
years of problem free operation.
However in the event of a defect in material or workmanship causing failure
of the unit within five years of the date of original purchase we will agree to
repair, or at our discretion replace, any defective item without charge for
labour or parts. To receive service under this warranty it is necessary to
return the unit to an LA Audio authorised service centre or to the factory
with a dated receipt as proof of purchase. After repair the unit will be
returned to you free of charge.
Limitations:
This warranty does not cover damage resulting from accident or misuse.
The warranty is void unless repairs are carried out by an authorised
service centre. The warranty is void if the unit has been modified other than
at the manufacturers instruction. The warranty does not cover components
which have a limited life, and which are expected to be periodically
replaced for optimal performance. We do not warrant that the unit shall
operate in any way other than as described in this manual.

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4.0 DESCRIPTION OF CONTROLS
4.1 INPUT SECTION
GAIN control
This control adjusts the sensitivity of the MPX10's input amplifier. GAIN
has different ranges depending on which input is selected -
MIC +10dB CCW (counter clockwise)
+60dB CW (clockwise)
LINE -10dB CCW
+20dB CW
DI 0dB CCW
+30dB CW
The LINE 0 mark on the GAIN control gives a unity gain setting for the Line
input.
CLIP led
Lights 3dB before maximum signal level to show transient peaks
approaching clipping.
Signals which cause the CLIP led to light briefly do not generally produce
audible distortion. However if the CLIP led lights continuously, reduce the
GAIN control (ccw) until CLIP led only lights occasionally.
LINE switch
This switch selects between Microphone input (switch out) or Line/DI input
(switch in) depending on the position of the Line/DI switch on the rear of the
unit.

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Fig 4.1.1 Input section rear panel showing the Line/DI switch
+48V switch
Pressing this switch applies +48V to both pins 2 and 3 of the Microphone
input connector. This Phantom Power voltage is commonly used to power
capacitor microphones and DI (direct injection) boxes via the input signal
cable.
To prevent the chance of damage to any external pieces of equipment, do
not use the +48V power option with unbalanced input sources ie. those
where pins 1 and 3 are connected together.
To avoid loud and potentially damaging electrical noise always turn down
monitor speakers and connect your microphone before switching phantom
power on.
PHASE switch
Reverses the phase of the input signal.
Mostly used for correcting out-of-phase connecting cables although there
are certain acoustic problems and specialised miking techniques which use
phase reversal.
FILTER switch
This switch inserts a 75Hz (-3dB frequency), 12dB/octave high pass filter
into the signal path after the input amplifier.
Useful for removing low frequency sounds such as rumble and stage noise.
Can also be used in conjunction with the EQ section to fatten bass sounds
without producing excessive low frequency energy.
4.2 NOISE REDUCTION & COMPRESSOR SECTION
NR (Noise Reduction) on the MPX10 is provided by a downward expander
which operates exactly opposite to a compressor. Signals falling below the
set Threshold are progressively attenuated rather than abruptly switched
off as with a noise gate. Also with a gate if the signal is a constant level and
just below threshold the gate will stay closed (no signal passes). With the
Expander there will be an output but at a reduced level. The further the input

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level falls the more the gain is reduced. Expander response is soft knee
around the onset of attenuation which combined with a low ratio (2:1) and
slow decay (similar to 'release' on a gate) time ensures transparent
operation.
The fast recovery (similar to 'attack' on a gate) time ensures that leading
transient edges are not lost.
NR THRESHOLD control
Sets the point at which the expander starts to attenuate. Threshold range is
0dB (reference +4dBu), CW to -70dB, fully CCW.
With the control fully CCW (-70dB) the expander will effectively remain
open.
EXP. led
Illuminates to show the onset of expansion ie. signal has fallen below
Threshold.
Please note unlike a gate led which shows that the gate is fully open or
closed, the EXP led lights to show the signal has fallen below the set
Threshold. The actual amount of signal attenuation is displayed on the GR
(Gain Reduction) meter.
COMPRESSOR THRESHOLD control
This control sets the signal level above which compression starts. The
Threshold range is -30dBu (CCW) to +20dBu (CW).
RATIO control
Ratio defines the amount of compression applied to the input signal once it
has exceeded the Threshold level. A Ratio setting of 2:1, for example
means that for every 2dB that the input exceeds the Threshold, the output
will increase by 1dB. The following graph shows the relationship between
input and output levels for various Ratios -
INPUT
OUTPUT 1:1
2:1
4:1
10:1
20:1
THRESHOLD
0dB
0dB

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Fig: 4.3.1 Effect of Ratio control on O/P levels.
A RATIO of 1:1 gives no compression and 20:1 causes effectively no
increase in output level no matter how far the signal increases above
Threshold. This is referred to as Limiting.
The ratio curves shown in Fig 4.3.1 are Hard-knee where the change in
gain is abrupt. The MPX10 has a Soft-knee control system which provides
a gradual change between compression levels.
ATTACK & RELEASE switch
The MPX10 compressor has 4 program dependant Auto Attack and
Release settings -
SLOW mode (switches 'out')
Attack = 20mS to 100mS Release = 2S
FAST mode (switches 'in')
Attack = 5mS to 70mS Release = 0.5S
In SLOW mode the compressor reacts to the average level of the input
signal and is the normal setting for most signal types. Fast transient signal
peaks will pass unaffected.

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Using FAST attack, the compressor reacts more to signal peaks and will
control all but the fastest transients.
DS switch
Pressing DS introduces a sibilant filter into the sidechain of the
compressor. This makes the compressor more sensitive to high frequency
'S' sounds. DS provides 8dB of compression at 8kHz (relative to 1kHz).
Please note this is broad-band de-essing and all frequencies are
compressed when an 'S' sound is detected. However this mthod works
well as most sibilant sounds occur at the beginning or end of words. Use
fast Attack and Release modes for de-essing.
BYPASS switch
Switches the compressor in and out of the signal path so that comparisons
can be made between compressed and un-compressed signals.
GAIN control
Because compression is a gain reduction process, the output of the
compressor is often at a lower level than the normal operating level.
Some way of restoring the signal to its pre-compressed level is required.
The Gain control provides adjustment to restore output level after
compression.
4.3 EQUALISER SECTION
The 4 band equaliser has fixed high and low frequency shelving sections
and two fully parametric mid sections.
LF control
Low frequency shelving equaliser. Provides ±15dB of cut or boost at 80Hz
LMF control
This control sets the amount of cut or boost for the LMF (Low Mid
Frequency) section. The Gain range on the MPX10 is ±15dB. The diagram
on the following page shows the effect of different cut and boost settings.

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Maximum cut or boost occurs at the centre frequency set by the
FREQUENCY control.
Qcontrol
Varies the 'Q' (bandwidth) of the cut or boost region. A low Q, CW (clock
wise) affects a wide band of frequencies whilst a high Q, CCW affects a
very small band. The Q control on the MPX10 has a range of 0.3 (3
octaves) to 12 (1/12th octave) - see the following diagram.
In general lower Qs are used when boosting and higher Qs when cutting -
see applications
FREQUENCY control
This control adjusts the centre frequency for LMF (Low Mid Frequency) cut
or boost. The LMF FREQUENCY control has a 40:1 range and is
adjustable from 60Hz, CCW to 2k4Hz (2.4kHz), CW - see the following
diagram.

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HMF control
Sets the amount of cut or boost for the HMF (High Mid Frequency) section.
FREQUENCY control
This control varies the cut or boost centre frequency for the HMF section.
Control range is 500Hz, CCW to 20kHz, CW.
Qcontrol
Varies the 'Q' of the cut or boost region for the HMF section.
HF control
High frequency shelving equaliser. Provides ±15dB cut or boost at 12kHz.
12kHz switch
Inserts a 12kHz, -6dB/octave filter into the post EQ signal path. The filter is
switched separately from the 4 band EQ and is available when the EQ is
bypassed.
BYPASS switch
Switches the 4 band equaliser in and out of circuit allowing A-B
comparisons on EQ settings.
Please note that the EQ 'output' on the rear of the unit is post BYPASS and
FILTER.
4.4 OUTPUT SECTION