Wheatstone FM-55 User manual

Digital auDio Processor
FM - 55
600 Industrial Drive, New Bern, North Carolina 28562 (tel [phone] / fax [phone] )
Technical
Manual

Technical
Manual
Wheatstone Corporation
August 2014
Digital auDio Processor
FM - 55

600 Industrial Drive
New Bern, North Carolina 28562
tel [phone] / fax [phone]
Wheatstone Digital Augio Processor Technical Manual
©2014 Wheatstone Corporation
FM-55 / Aug 2014
Ultra-HigH resolUtion Processing
ORSIS

Read Me!
FM-55 / Sep 2014
Attention!Attention!
Federal Communications Commission (FCC) Compliance
Notice:
Radio Frequency Notice
NOTE: This equipment has been tested and found to comply with the
limits for a Class A digital device, pursuant to Part 15 of the FCC rules. These
limits are designed to provide reasonable protection against harmful inter-
ference when the equipment is operated in a commercial environment. This
equipment generates, uses, and can radiate radio frequency energy and, if
not installed and used in accordance with the instruction manual, may cause
harmful interference to radio communications. Operation of this equipment
in a residential area is likely to cause harmful interference in which case the
user will be required to correct the interference at his own expense.
This is a Class A product. In a domestic environment,
this product may cause radio interference, in which case,
the user may be required to take appropriate measures.
This equipment must be installed and wired properly in order to assure
compliance with FCC regulations.
Caution! Any modications not expressly approved in writing by
Wheatstone could void the user's authority to operate this equipment.

IntroductIon - 1
FM-55 / Aug 2014
The History of Wheatstone Audio Processors
Introduced in 2005, the Vorsis product line evolved from Wheatstone’s return to
its original roots in audio processing. Having designed and integrated analog and
then, later, complex digital audio processing into our radio and television consoles
and control surfaces, Wheatstone was perfectly poised to address the challenges of
combining very high audio quality with competitive on air loudness.
Wheatstone audio processors are built to the same exacting standards as all
Wheatstone products. Research and development, manufacturing, testing, and qual‑
ity control for the line of audio processors are all accomplished within Wheatstone’s
large state‑of‑the‑art facility located in New Bern, North Carolina. Keeping everything
under one roof allows Wheatstone to have control over every facet of production
and ensures that our costumers receive products of the highest possible quality and
reliability. Staying true to “Made in the USA,” Wheatstone does not utilize offshore
manufacturing.
A dozen experts with deep experience in Digital Signal Processing, broadcast
audio and other engineering disciplines comprise our design team. Led by audio
processing expert and broadcast engineering veteran Jeff Keith, the team combines
their talents to design and build audio processors that achieve the highest standards
of on‑air sound quality.
In its short history Wheatstone Processing has already invented many new and
unique audio processing algorithms – algorithms that push audio processor perfor‑
mance to new and higher levels. Wheatstone was the rst to develop an intelligent,
“program density aware” AGC (2007 ‑ Sweet Spot Technology, or SST). We were
also the rst to employ the science of human psychoacoustics in the design of a mul‑
tiband limiter (2005, our acclaimed 31‑band limiter). In addition, our well‑regarded
Bass Management systems solve the bass intermodulation problems that plague other
brands of audio processors when pushed for competitive loudness.
Each Wheatstone Processing product comes with its ownWindows®software‑based
intuitive Graphical User Interface for control of the processor. Carefully tuned factory
presets ensure that our audio processors can be placed into use quickly and easily in
any size market with a minimum of effort.
ORSIS
Ultra-HigH resolUtion Processing

page Contents – 1
FM-55 / Aug 2014
CONTENTS
FM-55 Technical Manual
Chapter 1 - General Information
Table of Contents
Introduction....................................................................................1-2
FM-55 Feature Overview ...............................................................1-3
Rack Mounting...............................................................................1-3
FM-55 Installation Tips ...............................................................................................1-5
Grounding...............................................................................................................1-5
Surge Protection.....................................................................................................1-5
UPS/Power Conditioning........................................................................................1-5
Analog Audio Input Connections ............................................................................1-5
Analog Audio Output Connections .........................................................................1-6
Digital Audio/baseband192 Connections................................................................1-6
Where to Install the FM-55 .........................................................................................1-7
Digital STL..............................................................................................................1-7
Analog Left/Right STL ............................................................................................1-8
Composite Analog STL...........................................................................................1-8
Analog Phone Lines ...............................................................................................1-8
Where Should Pre-Emphasis Go? .........................................................................1-9
Ratings Encoders ...................................................................................................1-9
AC Power Considerations ............................................................1-9
Rear Panel Connections ..............................................................1-10
Audio Inputs...............................................................................................................1-10
Analog In ................................................................................................................1-11
AES In ....................................................................................................................1-11
SCA In ....................................................................................................................1-11
FM Audio Outputs......................................................................................................1-11
Analog Out..............................................................................................................1-11
AES/baseband192 Out...........................................................................................1-11
TX Out ....................................................................................................................1-12
Headphone Monitoring ..............................................................................................1-12
Network Connection ..................................................................................................1-12
Ethernet RJ-45 .......................................................................................................1-12
Typical Straight-Through Cable..............................................................................1-12
Typical Crossover Cable ........................................................................................1-13
General Purpose Interface (GPIO)............................................................................1-14
GPIO RJ-45............................................................................................................1-15
Processing Presets....................................................................................................1-15
FM-55 Input/Output Connections Drawing ................................................................1-17

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FM-55 / Aug 2014
CONTENTS
Meters.............................................................................................2-2
Input Level Meters......................................................................................................2-2
AGC Meters................................................................................................................2-2
Limiter Meters.............................................................................................................2-3
Output Meters.............................................................................................................2-3
OLED Display.................................................................................2-3
Headphone.................................................................................................................2-5
Source Selection .....................................................................................................2-5
Headphone Volume.................................................................................................2-5
Presets .......................................................................................................................2-5
Input............................................................................................................................2-5
Input Source ............................................................................................................2-5
Input Gain Adjustment.............................................................................................2-6
Pre-Emphasis.............................................................................................................2-6
Sound .........................................................................................................................2-6
Texture ....................................................................................................................2-6
EQ ...........................................................................................................................2-7
Save ........................................................................................................................2-7
A Note About The Front Panel Sound Adjustments ................................................2-7
Output.........................................................................................................................2-8
Network ......................................................................................................................2-9
Changing The Network Settings .............................................................................2-9
Leading Zeroes........................................................................................................2-9
Default IP Address...................................................................................................2-9
Vesions.......................................................................................................................2-9
Access.......................................................................................................................2-10
Getting Started...............................................................................3-4
Connecting With the GUI ..............................................................3-5
Configuring the GUI ......................................................................3-5
Connecting Directly Without a LAN ............................................................................3-5
The FM-55 and Internet Security Concerns ...............................................................3-6
About DHCP and the FM-55.......................................................................................3-6
The FM-55 Network Protocols and Ports Used ..........................................................3-6
Using the FM-55 GUI .....................................................................3-7
Dynamic Displays Region...........................................................................................3-8
Frequency-Domain Graph.......................................................................................3-8
Managing the Blue Dots - Tutorial...........................................................................3-8
Control Area Region..................................................................................................3-10
Input Menu..............................................................................................................3-11
Input Source .......................................................................................................3-11
Input Signal Presence ........................................................................................3-11
Input Failsafe......................................................................................................3-12
Analog Input Gain...............................................................................................3-12
Digital Input Gain................................................................................................3-12
L/R Balance........................................................................................................3-12
Phase Rotator.....................................................................................................3-12
Chapter 2 - FM-55 Front Panel
Chapter 3 - FM-55 PC GUI

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FM-55 / Aug 2014
CONTENTS
HPF - High Pass Filter........................................................................................3-13
Metering..............................................................................................................3-13
Equalizer Menu.......................................................................................................3-14
Manipulating Equalization Curves via Mouse ....................................................3-15
EQ Enable ..........................................................................................................3-15
Multiband Leveller Menu ........................................................................................3-16
A Word About Outboard Processors and Rreeveettbb.......................................3-16
iAGC Controls.....................................................................................................3-18
Gate Threshold...............................................................................................3-18
iAGC Attack....................................................................................................3-18
iAGC Release.................................................................................................3-18
RTZ Enable ....................................................................................................3-18
RTZ Down ......................................................................................................3-18
RTZ Up...........................................................................................................3-18
Multiband Leveller Controls................................................................................3-18
AGC Drive ......................................................................................................3-18
Gate Delay......................................................................................................3-18
Leveller Gate Mode ........................................................................................3-19
Leveller Gate Threshold .................................................................................3-19
Crossover Frequencies ..................................................................................3-19
Band Coupling and Key Band ........................................................................3-19
Multiband Leveller Dynamic Displays Menu.......................................................3-20
Threshold........................................................................................................3-22
Leveller Attack................................................................................................3-22
Leveller Release.............................................................................................3-22
Density............................................................................................................3-22
Compressor Attack.........................................................................................3-22
Compressor Release......................................................................................3-23
Ratio ...............................................................................................................3-23
AGC Mix .........................................................................................................3-23
Stereo Enhance..............................................................................................3-23
MB Limiter Menu ....................................................................................................3-25
Limiter and Clippers Controls .............................................................................3-25
Enable Limiters...............................................................................................3-25
Multiband Limiter Drive...................................................................................3-25
Limiter Knee ...................................................................................................3-26
Bass Clipper Threshold ..................................................................................3-26
Enable ............................................................................................................3-26
Bass Style 2....................................................................................................3-26
Main Clipper Drive..........................................................................................3-26
Pre-Emphasis.................................................................................................3-26
FM Diversity Delay .........................................................................................3-27
Limiters and Clippers Dynamic Displays Menu ..................................................3-27
Threshold........................................................................................................3-28
Attack..............................................................................................................3-28
Release ..........................................................................................................3-28
Stereo Generator Menu..........................................................................................3-29
Mode...................................................................................................................3-29
Test Oscillator.....................................................................................................3-29
MPX Output Configuration..................................................................................3-30
Composite Clipper Drive.................................................................................3-30
BS412 MPX Power Controller ........................................................................3-30

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FM-55 / Aug 2014
CONTENTS
Pilot Injection ..................................................................................................3-30
Pilot Phase .....................................................................................................3-30
MPX Output ...................................................................................................3-31
Multipath Limiter ............................................................................................3-31
Using the Multipath Limiter With Stereo Enhancement .................................3-32
Analog L/R Output .............................................................................................3-32
Analog L/R Output Level ................................................................................3-32
De-Emphasis..................................................................................................3-32
PreDelay.........................................................................................................3-33
Digital Output .....................................................................................................3-33
Digital Output Level ........................................................................................3-33
Baseband192 and AES Modes ......................................................................3-33
De-Emphasis.................................................................................................3-33a
PreDelay........................................................................................................3-33a
Sample Rate..................................................................................................3-33a
SCA Inputs ....................................................................................................3-33a
System Menu..........................................................................................................3-34
Input/Output Settings Change With Preset.........................................................3-34
Metering Data Over TCP/IP................................................................................3-35
System Status ....................................................................................................3-35
Security...............................................................................................................3-35
Remote Login .................................................................................................3-35
Front Panel.....................................................................................................3-36
GUI Access.....................................................................................................3-37
GUI Lock.........................................................................................................3-37
Side Bar Region ........................................................................................................3-38
Preset .....................................................................................................................3-38
Library.....................................................................................................................3-38
Locking Presets..................................................................................................3-39
How to View Preset Changes.............................................................................3-39
Save .......................................................................................................................3-40
Quick Save (QSave)...............................................................................................3-40
Devices...................................................................................................................3-41
Headphone Source.................................................................................................3-41
Headphone Control ................................................................................................3-41
Title Bar Region.........................................................................................................3-42
Status .....................................................................................................................3-42
Device.....................................................................................................................3-42
Current Preset ........................................................................................................3-42
Notes on Online and Offline Working .....................................................................3-43
Accessing Menu Options...........................................................................................3-44
File Menu Items......................................................................................................3-44
Hardware Menu Items ............................................................................................3-44
FM-55 Hardware Update....................................................................................3-44
Preset Menu Items .................................................................................................3-46
FM-55 / July 2015

page Contents – 5
FM-55 / Aug 2014
CONTENTS
General Specifications..................................................................A-3
Interpreting Common Audio Processing Terms.........................A-8
Background ................................................................................................................A-8
Audio Terms and Wheatstone Processing .................................................................A-9
Thump/Rumble/Bottom............................................................................................A-9
Punch/Boom/Tubby/Warm .....................................................................................A-10
Mud.........................................................................................................................A-10
Honk .......................................................................................................................A-10
Whack.....................................................................................................................A-10
Fuzzy/Tinny ............................................................................................................A-11
Sibilance.................................................................................................................A-11
Treble/Bright/Open .................................................................................................A-11
Finally .....................................................................................................................A-12
WheatNet-IP Configuration..........................................................A-14
Adding FM-55 to The WheatNet-IP System ..............................................................A-14
Appendix B
Appendix C
Appendices
Appendix A

page 1 – 1
FM-55 / Aug 2014
GENERAL INFORMATION
General Information
Introduction....................................................................................1-2
FM-55 Feature Overview ...............................................................1-3
Rack Mounting...............................................................................1-3
FM-55 Installation Tips...............................................................................................1-5
Grounding...............................................................................................................1-5
Surge Protection.....................................................................................................1-5
UPS/Power Conditioning .......................................................................................1-5
Analog Audio Input Connections............................................................................1-5
Analog Audio Output Connections.........................................................................1-6
Digital Audio/baseband192 Connections...............................................................1-6
Where to Install the FM-55.........................................................................................1-7
Digital STL ..............................................................................................................1-7
Analog Left/Right STL ............................................................................................1-8
Composite Analog STL ..........................................................................................1-8
Analog Phone Lines ...............................................................................................1-8
Where Should Pre-Emphasis Go?..........................................................................1-9
Ratings Encoders ...................................................................................................1-9
AC Power Considerations ............................................................1-9
Rear Panel Connections ..............................................................1-10
Audio Inputs ..............................................................................................................1-10
Analog In ................................................................................................................1-11
AES In.....................................................................................................................1-11
SCA In ....................................................................................................................1-11
FM Audio Outputs .....................................................................................................1-11
Analog Out .............................................................................................................1-11
AES/baseband192 Out...........................................................................................1-11
TX Out ....................................................................................................................1-12
Headphone Monitoring..............................................................................................1-12
Network Connection .................................................................................................1-12
Ethernet RJ-45 .......................................................................................................1-12
Typical Straight-Through Cable..............................................................................1-12
Typical Crossover Cable.........................................................................................1-13
General Purpose Interface (GPIO).............................................................................1-14
GPIO RJ-45 ............................................................................................................1-15
Processing Presets....................................................................................................1-15
FM-55 Input/Output Connections Drawing...............................................................1-17
Chapter Contents

page 1 – 2
FM-55 / Aug 2014
GENERAL INFORMATION
General Information
Introduction
Welcome to the Wheatstone FM-55 Digital Audio Processor. The FM-55 has been
carefully designed to deliver a clean and easy to listen to sound on the dial along with
very competitive loudness when that is the goal. The FM-55 expands on technologies
previously invented by Wheatstone, incorporates several new ones, and delivers that
“sought after” sound no matter what the market size. Like other Wheatstone processors,
the FM-55 has been carefully designed to not have a xed sound of its own – the end
user can use the FM-55’s vast pallet of tools to create any desired on-air sound.
The FM-55’s processing algorithms have been carefully evaluated though many
hours of critical listening with a very wide range of program material. The FM-55’s
processing algorithms deliver amazingly clean, clear, and if desired, loud, on-air sound.
Music sounds like it was meant to sound. Voices are rich and full and without unnatural
coloration or distortion. Transitions between widely varying program elements are deftly
handled, and if desired, with no trace of “processing” during spectral balance and density
corrections.
Remote control of the FM-55 is via a Windows-based Graphical User Interface (GUI)
software and can be accomplished via 100BaseT wired Ethernet. Up to four simultaneous
remote control sessions are possible. General Purpose Input/Output is provided on an
RJ-45 to interface to station systems.
The FM-55 utilizes an internal base sampling rate of 192 kHz. Higher sample rates
are used where it is benecial to do so, such as within the FM-55 clipper. A 24-bit, 144dB
internal dynamic range signal path allows audio to be processed with extreme precision.
The front panel OLED screen permits convenient control of system and basic processing
setup parameters and sound controls.
Those wishing for remote or PC control over all parameters will appreciate our
full-control GUI.This GUI is available free of charge and comes on a CD that accompanies
this product or can be downloaded at http://wheatstone-processing.com.

page 1 – 3
FM-55 / Aug 2014
GENERAL INFORMATION
Wheatstone products are designed and manufactured in our Corporate Headquarters
in New Bern, North Carolina, USA. This large, state-of-the-art facility affords complete
control over product quality during every step of the design and manufacturing process.
In order to maintain the high product quality that Wheatstone has been known for, no
offshore manufacturing is utilized.
The following pages will help you get the FM-55 up and running as quickly as
possible without having to know a lot of techie stuff.
If during installation or setup you nd that you need assistance or advice, please
feel free to contact our technical support folks at [phone] or email us at:
[email protected].
FM-55 Feature Overview
The FM-55 Audio Processor has been designed to process audio for conventional
analog FM.
Input audio can be analog or digital, with options on the digital input viaWheatNet-IP
or standard AES-3 connection. And input failover between the digital or analog inputs
is available.
Processing blocks include a phase rotator and high pass lter, a four band equilizer,
ve band iAGC processor and a ve band limiter.
The nal stage of the signal path utilizes a new clipper technology unique to the
FM-55. It’s followed by a composite processor which feeds the analog or digital
composite outputs simultaneously.
The FM-55 can be directly fed to an exciter in a number of ways. AES L/R may be
fed to an exciter if an all digital path is to be maintained. Conversely, the FM-55 can
also feed anAES composite signal to compatible exciters viaWheatstone’s baseband192
technology (MPX over AES).
Several dozen factory presets are provided with the FM-55, making a very wide
range of on air sounds and textures available to the user right out of the box. When
used in combination with the front panel’s Audio Processing Guru controls each factory
preset offers over a million different on-air sounds to the user.
The FM-55 is also equipped with Wheatstone’s ACI protocol, allowing complete
control of not only presets, but any parameter that is assigned to a user control (please
contact the factory for details on using this feature).
Rack Mounting
The FM-55 is designed to t into an industry standard 19" equipment rack, and
requires one rack unit (1.75") of vertical space. The unit has a depth of 9" behind the
rack rails (including chassis connectors), and its chassis has a width of 17-11/32". Space
needed in front of rack rails is 3/4" and an additional ve inches of space is required
for wiring cables to pass through. If using only two rack screws always use the bottom
two screws to prevent twisting of the front panel and other undue forces from harming
the processor chassis.
The FM-55 may be mounted between other devices in the equipment rack; however,
in accordance with good engineering practice it should not be mounted directly above

page 1 – 4
FM-55 / Aug 2014
GENERAL INFORMATION
devices that generate a signicant amount of heat (such as power ampliers or power
supplies). If such a location is unavoidable, then it is advisable to utilize an extra 1RU
blank rack panel between the FM-55 and devices imm ediately above and/or below it.
WARNING!
With very few exceptions, the FM-55 chassis DOES NOT need to be opened in the
eld.
Please be advised that the FM-55 contains high voltage power supply circuits
operating at voltages well above AC line input.
These voltages are hazardous and potentially deadly if accidentally contacted.
Special tools, software, and xtures are required for service. There are no
user‑serviceable parts inside.
The FM-55 unit must be returned to Wheatstone Corporation under a Return
Authorization in the unlikely event that repair is necessary.
If you need to return the FM‑55 to Wheatstone for repair, please
contact our ofce at 252-638-7000 Monday – Friday 8:30am to
5:30pm ET or after hours at [email protected] for a
Return Authorization (RA) number.

page 1 – 5
FM-55 / Aug 2014
GENERAL INFORMATION
FM-55 Installation Tips
Grounding
Establish a low impedance common ground in the facility and try to route all
equipment grounds to that point. Use ground conductors with the largest possible
surface area and keep ground leads as short as possible. The FM-55’s ground reference
is its chassis, which should be connected to the station ground. Such a connection is
especially important when the FM-55 is operated in a high RF environment because it
helps minimize differential voltages between the processor’s chassis and other pieces
of equipment such as the rack it is mounted within.
Surge Protection
Always place surge protection circuits as close as possible to the device being
protected. AC power line surge protection should manage transients in a way that keeps
instantaneous potential differences between the power line hot, neutral,AC grounding
conductor, the station ground, and the processor chassis as low as possible. Likewise,
measures should also be taken to keep the instantaneous potential difference between
the audio cable shields and the processor chassis as low as possible (this applies to
all audio equipment, not just the FM-55), particularly when the equipment is located
within the electrically hostile environment of a station’s transmitter facility.
UPS/Power Conditioning
Choose the best power conditioning/UPS units that your budget will allow, focusing
on the most important features and options that you actually need. Some questions to
ask while reviewing features are:
- How does the UPS behave when AC power is not exactly 60Hz, such as when
the facility is on its backup generator?
- If the UPS has onboard surge protection, what kind of surge capability does it
have and where are those surges directed to?
- Is the UPS equipped with remote monitoring capability?
- Does the UPS have onboard monitoring and alarms to signal problems such as
low batteries?
Analog Audio Input Connections
Balanced audio input sources should be connected to the FM-55 using standard
two-conductor shielded audio cable such as Belden 8451 or 9451.
Unbalanced input audio connections
should be made with shielded two
conductor cable. At the unbalanced
source’s output connect the “+” output
to FM-55’s “Hi” input (XLR pin 2) and
connect the shield wire to the FM-55’s
“Lo” input (XLR pin 3). If the cable’s
shield is used (recommended) connect it
at the FM-55 end only (XLR pin 1) to
prevent AC ground loops.

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FM-55 / Aug 2014
GENERAL INFORMATION
If RF interference is an issue, the far (oating
and ungrounded) end of an audio cable
shield can be experimentally bypassed to
RF ground via a 0.01µF, 250V AC rated
capacitor. Suitable capacitors are:
TDK CS17-F2GA103MYGS
Murata DE2F3KH103MA3B
Panasonic ECK-ATS103MF
AVX 65N103MBLCP
Analog Audio Output Connections
Balanced audio loads are recommended and should be connected to the FM-55’s outputs
using standard two-conductor shielded audio cable. Unbalanced audio loads should be
avoided, but if they can’t they should be connected using shielded two conductor cable
such as Belden 8451 or 9451 (as if connecting a balanced source).
The FM-55 is equipped with active balanced output stage that behaves like a transformer.
Because of this behavior the correct wiring method may be different than expected.
The unbalanced load’s “Hi” lead should be
connected to XLR connector Pin
2 (“Hi”).
The unbalanced load’s shield should be
connected to the FM-55’s output XLR Pin 3
(“Lo”). Then, and to enable the FM-55’s
balanced output amplier to operate correctly when driving the unbalanced load, it is
recommended that the FM-55’s XLR output Pin 1 (ground/shield) also be connected to
Pin 3 (“Lo”), noting that this MUST BE DONE at the FM-55’s output connector (see
the diagram above).
Note that it is not advisable to connect Pin 1 and Pin 3 conductors together at the far
end of the cable. Doing so can induce external noise and crosstalk on the output amplier’s
“load sense” lead which is XLR Pin 3 when Pin 2 is being used as the “Hot.”
As in the input case, if RF interference is
an issue the far (oating) end of the cable
shield can be experimentally bypassed to
RF ground through a 0.01µF 250V AC
rated capacitor to see if it helps. Please
refer to the listing above for capacitors
known to be suitable for this task.
Digital Audio/ baseband192 Connections
For digital audio connections always use a good quality digital audio cable (or twisted
pair Category 5E/6 Network cable) having a characteristic impedance of 110 ohms. This
cable should be shielded where possible, and in the case of multi-pair cable, each pair
should be individually shielded. Foil shielding is recommended for permanent installations,
and a cable with foil shield plus an overall braid should be used in applications where
frequent exing of cables might occur.

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FM-55 / Aug 2014
GENERAL INFORMATION
Generic “audio” cable such as Belden 8451 and 9451 may sometimes be used for
interconnecting AES3 digital audio devices as long as the cable is short. The actual
cable length that will work satisfactorily is determined by many factors including the
error correction and jitter tolerance of the AES3 receiver, the characteristics of the
digital cable driver and the characteristics of the specic cable being used and its length.
“Generic” analog audio cables usually have higher capacitance than digital cable and
high capacitance cables can impair the ability of the AES3 receiver to recover the digital
signal without errors. Increased jitter, dropouts, or no audio at all can be an indication
of an improper cable type.
Where to Install the FM-55
The best location to install the FM-55 is at the transmitter site. This requires that
a discrete Left/Right STL, either analog or digital, be involved in the signal path. The
major benet of a transmitter site installation is that it enables the use of the FM-55’s
built-in lab-grade stereo encoder which allows much tighter control of modulation peaks.
A transmitter site location has the additional benet of allowing the use of the FM-55’s
highly oversampled composite processor to gain an additional loudness advantage.
The Wheatstone composite processor is much cleaner and more forgiving than those
in other products, and in combination with the FM-55’s tight pilot and SCA protection
lters can create additional loudness without the audible grunge that composite clippers
typically create.
With the advent of Wheatstone’s baseband192 technology, the promise of an all
digital airchain that is as loud as its analog composite sibling is now a reality. Users
now have the option of deploying the FM‑55 and other Wheatstone processors using
traditional analog or MPX over AES with a compatible exciter.
We recommend that, whenever there is a choice between using an exciter’s composite
MPX, AES over MPX option, or AES3 input, the processor (any processor) should be
interfaced to the transmitter using the exciter’s AES over MPX or analog composite
stereo multiplex input. The exciter’s AES3 digital input may be “clean” and it may be
“digital,” but it also precludes the ability to gain additional loudness through the use
of the FM-55’s intelligent oversampled composite clipper. Also, depending on factors
including the sample rates being used the exciter’s AES digital input can exhibit inferior
peak control compared to the exciter’s composite input.
When the FM-55 is located at the studio and an STLis being used to send the program
material to the transmitter site there are several issues to consider:
Digital STL
There are two categories of Digital STL’s on the market – those with codec-based
audio compression and those with uncompressed linear audio.
When a digital STL employs codec-based audio compression the FM-55 should be
located at the transmitter site which places it after the codec. This is very important
because most codecs will sound better when presented with unprocessed studio audio
instead of highly processed and pre-emphasized audio from the processor’s output.
Further, the encoding schemes used in such STL’s cannot accurately pass the well-dened
peak levels created by the FM-55, creating a modulation (loudness) disadvantage.

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FM-55 / Aug 2014
GENERAL INFORMATION
Installing the FM-55 at the studio end of a “compressed” STL brings with it at least
two caveats:
- The FM-55 stereo generator and composite clipper will not be available. Many
digital exciters offer stereo generator and composite clipper functions, but their
clippers have historically been quite crude and spectrally “dirty” compared to
the FM-55’s exceptional clipper. Therefore exciter hosted composite clippers are
not the optimum choice when the station’s ultimate sound quality is important.
- Compressed STL’s do not perform well when presented with competitively
processed audio, especially when that audio is pre-emphasized. This is because
codecs do their work by examining the audio for opportunities to remove content
that shouldn’t be audible to the average human ear. When densely processed audio
is presented to a codec, there are fewer opportunities to remove redundant audio
information and then mask that removal from our hearing. When handling heavily
processed (limited dynamic range) material codec operation can be much more
obvious – even to the point of being objectionable – than when the processing
is located after the codec where the masked artifacts are only occasionally and,
usually, minimally unmasked by processing gain.
Uncompressed (linear) digital STL’s have only one major installation limitation –
placing the FM-55 at the studio end of the STL will preclude the use of the stereo
generator and composite clipper.
TIP: If using the FM-55 at the studio be certain that any clippers and emphasis in the
stereo generator at the transmitter site are properly set up to complement the settings in
FM-55. This will prevent gross distortion and potentially large modulation overshoots.
Analog Left/Right STL
Older analog discrete left/right STL’s can suffer from an inability to control audio
peaks because of inadequate bandwidth in their IF circuits and/or poor low frequency
and phase performance. Individual left/right STL’s rarely have identical group delay
and this will adversely affect stereo separation when the signal is nally converted to
the multiplex composite domain. Such STL’s can also suffer from AFC bounce when
handling highly processed low frequency material, robbing modulation and reducing
on-air loudness.
Composite Analog STL
A high quality analog composite STL can have advantages over an analog left/right
STL in that it will typically have broader audio bandwidth and better audio performance
than discrete analog STL. Most also have the capability to add subcarriers for SCA and
RDS along with the composite audio. This means that many SCA and RDS generators
may be located at the studio end of the STL, which, along with the audioprocessor, makes
for a very convenient setup. With a modern composite STL and properly engineered
point-to-point path, the audio can be nearly as transparent as a digital STL.
Analog Phone Lines
Discrete left/right analog “phone line” STL’s are not recommended because of the
inability of most Telco service providers to meet the at frequency response and phase
matching requirements. Furthermore, in many countries wideband analog circuits have

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FM-55 / Aug 2014
GENERAL INFORMATION
become unavailable or their cost prohibitive. On the other hand if the wired STL is a
dedicated (and equalized if necessary) pair of circuits that is under the station’s full
control it may be acceptable.
Where Should Pre-Emphasis Go?
Pre-emphasis should always be applied by the audio processing, and never by
the exciter. Modern FM audio processors are equipped with highly rened and very
sophisticated technology to manage the myriad challenges posed by FM pre-emphasis.
They can provide very tight modulation control with very low perceived distortion.
No FM exciters have this technology.
To summarize: the best location overall for the audio processor is always at the
transmitter.
Ratings Encoders
Field experience has been that Wheatstone audio processors favorably pass the
data watermarking scheme used in the rating service technology, regardless of the
aggressiveness of the processing being performed.
AC Power Considerations
Please note that in order to enhance its long-term reliability, the FM-55 has no
power switch because all power switches notoriously become intermittent over time
without regular use.
The FM-55 accepts AC line input voltages between 90 and 260 VAC, 50 or 60Hz.
Power consumption is under 100VA.
Although aggressive AC input ltering is utilized on the AC power input it is always
advisable to use external surge protection and an uninterruptible power supply (UPS)
wherever possible, especially where the AC power quality can be in question, such
as at a remote transmitter site.
Power conditioning, surge suppression, and even power backup devices are wise
investments when using sensitive modern electronic devices. The FM-55 is, after all,
a highly specialized “computer.”
The use of a UPS as recommended will protect the FM-55 from short duration
power interruptions and glitches which might otherwise signal it to reboot. When the
FM-55 reboots there will be a loss of audio for approximately 15 seconds.

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FM-55 / Aug 2014
GENERAL INFORMATION
Rear Panel Connections
The image below shows the rear panel of the FM55 and the location of various
connectors associated with an installation:
Audio Inputs
The FM-55 accepts three types of audio input sources:
• Balanced analog line level left/right audio;
• Digital AES3 compliant left/right audio with sample rates between 32kHz and 96kHz;
• WheatNet-IP via 100BaseT Ethernet connection to a WheatNet-IP audio network.
Input audio can be applied to any or all inputs simultaneously with the caveat that
the WheatNet-IP input and AES3 inputs share a common digital path into the internal
processing.
Automatic audio failover from analog to digital or vice versa is supported. Automatic
failover from AES3 or WheatNet-IP to analog is instantaneous and based on invalid or
missing bits in the AES3 or WheatNet-IP stream, or after 30 seconds of “silence” (level
below -42dBFS).
Automatic failover from analog to AES3 or WheatNet-IP is based on silence sense
responding to audio on both channels being below -42dBFS for more than 30 seconds.
Failover capability is not available between the AES and WheatNet-IP inputs.
CONNECTOR TYPE FUNCTION & NOTES
1 XLR Female Left Analog Input
2 XLR Female Right Analog Input
3 XLR Male Left Analog Output (FM processed Audio)
4 XLR Male Right Analog Output (FM processed Audio)
5 BNC Female SCA Input #1 (for reliable connection use 50 Ohm male connector)
6 BNC Female SCA Input #2 (for reliable connection use 50 Ohm male connector)
7 BNC Female TX Output #1 (for reliable connection use 50 Ohm male connector)
8 BNC Female TX Output #2 (for reliable connection use 50 Ohm male connector)
9 XLR Female AES Audio Input
10 XLR Male AES Audio Output (switchable between L/R and baseband192)
11 RJ-45 GPI Interface
12 RJ-45 Ethernet (Network) Connection / WheatNet-IP audio connection
13 IEC Mains connection (90-240~VAC / 50-60Hz)
FM-55 Rear Panel Connections (left to right)