Orban Optimod-FM 5518 Stereo Encoder/Limiter

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OPTIMOD-FM 5518 is a new superb stand-alone stereo encoder combining look-ahead and band-limited clipping techniques to control STL-induced overshoots while minimizing artifacts.


User-Friendly Interface:

LCD and full-time LED meters

An LCD and full-time LED meters make setup, adjustment and programming of OPTIMODFM easy – you can always see the metering while you are adjusting the processor. Navigation is by dedicated buttons, soft buttons (whose functions are context-sensitive), and a large rotary knob. The LEDs show all metering functions.

(input/output, Limiting)

Universal transmitter protection for FM broadcast

The 5518 provides universal transmitter protection for FM broadcast. It can be configured to interface ideally with any commonly found transmission system in the world.

Pre-emphasis limiting for the two standard pre-emphasis curves of 50 µs & 75 µs

The 5518 provides pre-emphasis limiting for the two standard pre-emphasis curves of 50 µs and 75 µs. Its pre-emphasis control is seldom audibly apparent, producing a clean, open sound with subjective brightness matching the original program.

Tight peak control at all its outputs

The 5518 achieves extremely tight peak control at all its outputs — analog left/right, AES3 left/right, and composite baseband.

Stereo encoder has two outputs with independent level controls.

The stereo encoder has two outputs with independent level controls, each capable of driving 75 Ω in parallel with 47,000 pF (100 ft / 30 m of coaxial cable).

Bandwidth-limiting & overshoot compensation

The 5518 prevents aliasing distortion in subsequent stereo encoders or transmission links by providing bandwidth-limiting and overshoot-compensated 15 kHz low-pass filters ahead of the 5518’s audio outputs and stereo encoder.

Anti-aliased clippers

Anti-aliased clippers running at 256 kHz sample-rate prevent any trace of “digital clipper” sound.

Flexible Configuration:

Analog & AES3 digital inputs & outputs

The 5518 includes analog and AES3 digital inputs and outputs. Both digital input and digital output are equipped with sample-rate converters and can operate at 32 kHz, 44.1 kHz, 48, 88.2 and 96 kHz samplerates. The pre-emphasis status and output levels are separately adjustable for the analog and digital outputs. The input failsafe feature allows the 5518 to automatically switch from its digital input to its analog input (or vice-versa) if the primary input suffers a loss-of-audio failure.

Transformerless, balanced 10 kΩ instrumentation-amplifier circuits

The analog inputs are transformerless, balanced 10 kΩ instrumentation-amplifier circuits, and the analog outputs are transformerless balanced, and floating (with 50 Ω impedance) to ensure highest transparency and accurate pulse response.

Two independent composite baseband outputs with digitally programmable output levels

The 5518 has two independent composite baseband outputs with digitally programmable output levels. Robust line drivers enable them to drive 100 feet of RG-59 coaxial cable without audible performance degradation.

Two subcarrier inputs

The 5518 has two subcarrier inputs that are mixed with the output of OPTIMOD-FM’s stereo encoder before application to the composite output connectors. One input can be re-jumpered to provide a 19 kHz pilot reference output. Each input has an internal level trim to accommodate subcarrier generators with output levels as low as 220 mV.

Precise control of audio bandwidth to 15 kHz

The 5518 precisely controls the audio bandwidth to 15 kHz. This prevents overshoots in uncompressed digital links operating at a 32 kHz sample-rate and prevents interference to the pilot tone and RDS (or RBDS) subcarrier.

Defeatable, extremely accurate multiplex power limiter

The 5518 has a defeatable multiplex power limiter that controls the multiplex power to ITU-R BS412 standards. The multiplex power limiter acts on all outputs (not just the composite output). It reduces clipper drive when it reduces power, simultaneously reducing clipping distortion. To prevent audible gain pumping, a user-adjustable gain offset control allows the user to minimize the amount of gain control that the controller performs.

10 MHz clock / wordclock reference input

The 5518 has a 10 MHz clock / wordclock reference input, which can be used to lock the stereo pilot tone to a high precision external reference like a GPS-based frequency standard. This facilitates using the 5518 in single-frequency network applications.

Samplerate and multiples thereof

The sample-rate is 64 kHz and multiples thereof, up to 512 kHz. The internal audio bandwidth is high enough to prevent overshoot caused by spectral truncation of the left/right input signals that are band-limited to 18 kHz or lower.

Low-pass filtering

15, 16 or 17 kHz linear-phase low-pass filtering can be applied to the input signal. To minimize input/output delay, this filter can be bypassed, which is appropriate if the input signal is correctly band-limited by the audio processor driving the 5518.

Left/right domain overshoot limiter

A left/right domain overshoot limiter is available. This uses the same technology as Orban’s 8218 stand-alone stereo encoder, combining look-ahead and band-limited clipping techniques to control STL-induced overshoots while minimizing artifacts.

Dual-mode composite limiter

A dual-mode composite limiter is available. It can operate in either “Half-Cosine Interpolation” mode or conventional hard clipper mode. The “Half-Cosine” mode provides

better separation and preservation of stereo imaging, while the “Hard” mode provides brighter sound because it creates waveforms that are closer to square waves. Both modes provide excellent spectral protection of the pilot tone and subcarrier regions. To ensure accurate peak control, the limiter operates at 512 kHz sample-rate.

J.17 de-emphasis

The 5518 can apply J.17 de-emphasis to the input signal.

ITU412 multiplex power controller

A high-accuracy ITU412 multiplex power controller is available, with user control over the multiplex power threshold. This allows you to compensate for overshoots in the signal path upstream from the 5518, preventing excessive reduction of the multiplex power.

SSB Stereo Encoder Operation

The 5518 allows its stereo encoder’s stereo subchannel modulator to operate in an experimental compatible single sideband/vestigial sideband mode.

Flat or pre-emphasized input signal

The input signal can be flat or pre-emphasized to 50 µs or 75 µs.

Silence alarm and digital audio fault tally outputs

Silence alarm and digital audio fault tally outputs are available.

Inputs and outputs

All normal 5518 inputs and outputs are available, including analog and digital inputs, two composite outputs with independent level controls and two subcarrier inputs (one of which can be repurposed to emit a 19 kHz pilot reference output for RDS/RBDS generators.


Eight programmable, optically isolated “general-purpose-interface” (GPI) ports

The 5518 can be remote-controlled by 5 – 12V pulses applied to eight programmable, optically isolated “general-purpose interface” (GPI) ports.

5518 PC Remote software

5518 PC Remote software is a graphical application that runs under Windows 2000/XP/Vista/7/8. It communicates with a given 5500 via TCP/IP over modem, direct serial and Ethernet connections. You can configure PC Remote to switch between many 5518s via a convenient organizer that supports giving any 5518 an alias and grouping multiple 5518s into folders. Clicking a 5518’s icon causes PC Remote to connect to that 5518 through an Ethernet network, or initiates a Windows Dial-Up or Direct Cable Connection if appropriate. The PC Remote software allows the user to access all 5518 features (including advanced controls not available from the 5518’s front panel), and allows the user to archive and restore presets, automation lists, and system setups (containing I/O levels, digital word lengths, GPI functional assignments, etc.).

Versatile real-time clock

OPTIMOD-FM contains a versatile real-time clock, which allows automation of various events (including recalling presets) at pre-programmed times. The clock can be synchronized automatically to an Internet timeserver.

Bypass Test Mode

A Bypass Test Mode can be invoked locally, by remote control (from either the 5518’s GPI port or the 5518 PC Remote application) or by automation to permit broadcast system test and alignment or “proof of performance” tests.

Built-in line-up tone generator

OPTIMOD-FM contains a built-in line-up tone generator, facilitating quick and accurate level setting in any system.

Upgradeable Software

OPTIMOD-FM’s software can be upgraded by running Orban-supplied downloadable upgrade software on a PC. The upgrade can occur remotely through the 5518’s Ethernet port or serial port (connected to an external modem) or locally (by connecting a Windows® computer to the 5518’s serial port through the supplied null modem cable).

Rigorously RFI-suppressed input, output & power connections

All input, output and power connections are rigorously RFI-suppressed to Orban’s traditional exacting standards, ensuring trouble-free installation.


The 5518 is designed and certified to meet all applicable international safety and emissions standards.


Technical Specification


Specifications apply for measurements from analog left/right input to stereo composite out-put and to FM analog left/right output.

Frequency Response (Bypass Mode): Follows standard 50μs or 75μs pre-emphasis curve ±0.10 dB, 2.0 Hz–15 kHz. Analog left/right output and digital output can be user-configured for flat or preemphasized output.

Noise: <–85 dB below 100% modulation, 30-15,000 Hz, deemphasized.

Total System Distortion (de-emphasized, 100% modulation): <0.01% THD, 20 Hz–1 kHz, rising to <0.05% at 15 kHz. <0.02% SMPTE IM Distortion.

Total System L/R Channel Separation: >55 dB, 20 Hz – 15 kHz; 60 dB typical.

Polarity (Two-Band and Bypass Modes): Absolute polarity maintained. Positive-going signal on input will result in positive-going signal on output.

Processing Sample Rate: The 5518 is a “multirate” system, using internal rates from 64 kHz to 512 kHz as appropriate for the processing being performed. L/R overshoot limiters operate at 256 kHz (and are anti-aliased), while the composite limiter operates at 512 kHz.

Processing Resolution: Internal processing has 24 bit (fixed point) or higher resolution.

Audio Input

Configuration: Stereo.

Impedance: >10kΩ load impedance, electronically balanced1.

Nominal Input Level: Software adjustable from –9.0 to +13.0 dBu (VU).

Maximum Input Level: +27 dBu.

Connectors: Two XLR-type, female, EMI-suppressed. Pin 1 chassis ground, Pins 2 (+) and 3 electronically balanced, floating and symmetrical.

A/D Conversion: 24 bit 128x oversampled delta sigma converter with linear-phase anti-aliasing filter.

Filtering: RFI filtered.

Analog Audio Output

Configuration: Stereo. Flat or pre-emphasized (at 50μs or 75μs), software selectable.

Source Impedance: 50Ω, electronically balanced and floating.

Load Impedance: 600Ω or greater, balanced or unbalanced. Termination not required or recommended.

Output Level (100% peak modulation): Adjustable from –6 dBu to +24 dBu peak, into 600Ω or greater load, software-adjustable.

Signal-to-Noise: >= 90 dB unweighted (Bypass mode, de-emphasized, 20 Hz–15 kHz bandwidth, referenced to 100% modulation).

L/R Crosstalk: <= –70 dB, 20 Hz–15 kHz.

Distortion: <= 0.01% THD (Bypass mode, de-emphasized) 20 Hz–15 kHz bandwidth.

Connectors: Two XLR-type, male, EMI-suppressed. Pin 1 chassis ground, Pins 2 (+) and 3 electronically balanced, floating and symmetrical.

D/A Conversion: 24 bit 128x oversampled, with highpass filter at 0.15 Hz (–3 dB).

Filtering: RFI filtered.

Digital Audio Input

Configuration: Stereo per AES3 standard, 24 bit resolution, software selection of stereo, mono from left, mono from right or mono from sum.

Sampling Rate: 32, 44.1, 48, 88.2, or 96 kHz, automatically selected.

Connector: XLR-type, female, EMI-suppressed. Pin 1 chassis ground, pins 2 and 3 transformer balanced and floating, 110Ω impedance.

Input Reference Level: Variable within the range of –30 dBFS to –10 dBFS.

J.17 Deemphasis: Software-selectable.

Filtering: RFI filtered.

Digital Audio Output

Configuration: Stereo per AES3 standard. Output configured in software as flat or pre-emphasized to the chosen processing pre-emphasis (50µs or 75µs), with or without J.17 pre-emphasis.

Sample Rate: Internal free running at 32, 44.1, 48, 88.2 or 96 kHz, selected in software. Can also be synced to the AES3 digital input at 32, 44.1, 48, 88.2 or 96 kHz, as configured in software.

Word Length: Software selected for 24, 20, 18, 16 or 14-bit resolution. First-order high-pass noiseshaped dither can be optionally added, dither level automatically adjusted appropriately for the word length.

Connector: XLR-type, male, EMI-suppressed. Pin 1 chassis ground, pins 2 and 3 transformer balanced and floating, 110Ω impedance.

Output Level (100% peak modulation): –20.0 to 0.0 dBFS software controlled.

Filtering: RFI filtered.

Wordclock/10 MHz Sync Reference Input

Configuration: Accepts 1x wordclock or 10 MHz reference signals, automatically selected. The DSP master clock can be phase-locked to these signals, which in turn phase-locks the 19 kHz pilot tone frequency, facilitating singe-frequency network operation. The digital output sample frequency can also be locked to these signals.

Level: Unit will lock to 1x wordclock and 10 MHz squarewaves and sinewaves having a peak value of 0.5 V to 5.0 V.

Connector: BNC female, grounded to chassis, non-terminating to allow reference signals to be looped through via an external BNC “tee” connector (not supplied).

Composite Baseband Output

Configuration: Two outputs, each with an independent software-controlled output level control, output amplifier and connector.

Source Impedance: 0Ω voltage source or 75Ω, jumper-selectable.

Load Impedance: 37Ω or greater. Termination not required or recommended.

Maximum Output Level: +16.0 dBu (13.82Vp-p).

Pilot Level: Adjustable from 6.0% to 12.0%, software controlled.

Pilot Frequency Stability: 19 kHz, ±1.0 Hz (10 degrees to 40 degrees C).

D/A Conversion: 24-bit

Signal-to-Noise Ratio: >= 85 dB (Bypass mode, de-emphasized, 20 Hz – 15 kHz bandwidth, referenced to 100% modulation, unweighted).

Distortion: <= 0.02% THD (Bypass mode, de-emphasized, 20 Hz – 15 kHz bandwidth, referenced to 100% modulation, unweighted).

Stereo Separation: > 55 dB, 30 Hz-15 kHz. 65 dB typical at 400 Hz.

Crosstalk-Linear: <= –80 dB, main channel to sub-channel or sub-channel to main channel (referenced to 100% modulation).

Crosstalk-Non-Linear: <= –80 dB, main channel to sub-channel or sub-channel to main channel (referenced to 100% modulation).

38 kHz Suppression: >= 70 dB (referenced to 100% modulation).

76 kHz & Sideband Suppression: >= 80 dB (referenced to 100% modulation).

Connectors: Two BNC, shell connected to chassis ground, EMI suppressed.

Maximum Load Capacitance: 0.047 µF (0Ω source impedance). Maximum cable length of 100 feet/30 meters RG–58A/U.

Filtering: RFI filtered.

Subcarrier (SCA) Inputs

Configuration: Two subcarrier inputs sum directly into composite baseband outputs; COMPx LVL control settings have no effect on the absolute subcarrier levels.

Impedance: 600Ω

SCA Sensitivity: Variable from <100 mV p-p to >10 V p-p to produce 10% injection assuming 100% modulation = 4 V p-p at the 5518’s composite outputs.
Rear-panel accessible PC-board-mounted trim pots allow user to adjust the sensitivities of the two SCA inputs.

Connectors: Two BNC, shell connected to chassis ground, EMI suppressed.
19 kHz Pilot Reference: SCA2 input can be re-jumpered to provide a 19 kHz pilot reference output.

Remote Computer Interface

Supported Computer and Operating System: IBM-compatible PC running Microsoft Windows® 2000 (SP3 or higher), XP, Vista,7 or 8.

Configuration: TCP/IP protocol via direct cable connect, modem, or Ethernet interface. Suitable null modem cable for direct connect is supplied. Modem and other external equipment is not supplied. Serial Connector: RS–232 on DB–9 male connector, EMI-suppressed. Uses PPP to pro-vide for direct or modem connection to the 5518 PC Remote application.

Ethernet Connector: Female RJ45 connector for 10-100 Mbps networks using CAT5 cabling. Native rate is 100 Mbps. Provides for connection to the 5518 PC Remote application through either a network, or, using a crossover Ethernet cable, directly to a computer.

Ethernet Networking Standard: TCP/IP.

Remote Control (GPI) Interface

Configuration: Eight (8) inputs, opto-isolated and floating.

Voltage: 6–15V AC or DC, momentary or continuous. +12VDC provided to facilitate use with contact closure.

Connector: DB–25 male, EMI-suppressed.

Control: User-programmable for any eight of user presets, factory presets, bypass, test tone, stereo or mono modes, analog input, digital input.

Filtering: RFI filtered.

Tally Outputs

Circuit Configuration: Two NPN open-collector outputs.

Voltage: +15 volts maximum. Do not apply negative voltage. When driving a relay or other inductive load, connect a diode in reverse polarity across the relay coil to protect the driver transistors from reverse voltage caused by inductive kickback.

Current: 30 mA maximum

Indications: Tally outputs can be programmed to indicate a number of different operational and fault conditions, including Input: Analog, Input: Digital, Analog Input Silent, AES In-put Silent, and AES Input Error.


Voltage: 85–264 VAC, 50–60 Hz, 30 VA.

Connector: IEC, EMI-suppressed. Detachable 3-wire power cord supplied.

Fuse: 2.5A 20mm Quick Acting HBC, mounted on the power supply circuit board.

Grounding: In order to meet EMI standards, circuit ground is hard-wired to chassis ground. To avoid ground loops, we recommend using an FM exciter with a balanced composite input.

Safety Standards: ETL listed to UL standards, CE marked.


Operating Temperature: 32° to 122° F / 0° to 50° C for all operating voltage ranges.

Humidity: 0–95% RH, non-condensing.

Dimensions: (W x H x D): 19″ x 1.75″ x 14.25″ / 48.3 cm x 4.5 cm x 36.2 cm. One rack unit high.

Humidity: 0–95% RH, non-condensing.

RFI/EMI: Tested according to Cenelec procedures. FCC Part 15 Class A device.

Shipping Weight: 10 lbs / 4.6 kg

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