DISCONTINUED Orban Optimod-FM 8500 Audio Processor

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Introducing Optimod-FM 8500: Orban’s new flagship processor and the next step beyond the Optimod-FM 8400. The 8500 builds on the proven, competitive sound of 8400 version 3 while adding features that make it the ideal choice for FM stations simultaneously transmitting iBiquity’s HD Radio®, Eureka 147, or a netcast (where it works particularly well with Orban’s aacPlus® Opticodec-PC® LE). “Under the hood,” they redesigned all of the circuitry using the latest components. They also doubled the DSP power, so the DSP not only supports the new features but also provides comfortable headroom for future DSP improvements.


Featuring versatile five-band and two-band processing for both analog FM transmission and digital radio, the 8500 provides the industry’s most consistent sound, track-to-track and source-to-source. This consistency allows you to create a sonic signature for your station with the assurance that your signature will stay locked in, uniquely branding your sound.

The 8500 provides stereo enhancement, equalization, AGC, multiband compression, low-IM peak limiting, stereo encoding, and composite limiting — everything that even the most competitive major market station needs to stand out on the dial.

More than 20 excellent sounding, format specific factory presets get you started. You’ll find all of your favorite 8400 version 3 factory presets, plus some new ones designed by Bob Orban and Greg Ogonowski to please any broadcaster. Although the factory presets are fully competent “out of the box,” you can customize them with easy one-knob LESS-MORE control or with more than 60 advanced controls, whose versatility will satisfy even the most finicky on-air sound designer. If you have created custom presets for your 8400, you’ll find that they import perfectly into the 8500, retaining your carefully crafted sound.

Effective 16 kHz band limiting on the analog-FM left/right output (analog or AES3) allows this signal to pass through a 32 kHz uncompressed STL without added overshoot—44.1 or 48 kHz channels are not required. If you choose to use the 8500’s superb DSP-based stereo encoder and composite limiter, be assured that they deliver an FM analog signal that is always immaculately clean and perfectly peak limited, with full spectral protection of subcarriers and RDS/RBDS regardless of the amount of composite limiting.

Processing for digital radio/netcast (DR) is now supplied standard. Orban increased the base sample rate of all processing to 64 kHz so the DR output can readily provide 20 kHz audio bandwidth for those who prefer it. Moreover, a built-in 8-second delay in the analog processing path vastly improves installation versatility in HD Radio plants, freeing you from the need to use the delay line built into the HD Radio exciter. This allows you to use the 8500’s built-in stereo encoder and composite limiter to drive the analog FM transmitter, ensuring no-compromise analog-channel loudness.

The 8500’s digital radio processing contains look ahead peak limiting that operates in parallel with the FM-channel peak limiting. Orban optimized the look-ahead limiting to make the most of the limited bit-rate codec typically used in the digital channel. By eschewing any clipping, the digital radio processing prevents the codec from wasting precious bits encoding clipping distortion products, allowing the codec to use its entire bit budget to encode the desired program material.

The look-ahead limiter receives the output of a new mixer that sets the balance of each processing band for the digital channel, independent of the balance in the FM processing. The bottom line? Processing that optimizes the sound of your FM channel while punching remarkably crisp, clean, CD-like audio through to your digital channel audience.

Orban haven’t forgotten pure analog FM broadcasters. If you defeat the 8-second delay, you’ll find that the 8500’s base throughput delay has decreased by almost 4 milliseconds compared to the 8400. This makes off-air headphone monitoring even more comfortable for talent. Of course, we’ve retained the 8400’s “headphone monitor” output option, which now has a negligible 2-millisecond delay regardless of the processing structure on-air. Orban have also added the “ultra-low-latency” structure first introduced in Optimod-FM 8300. This structure yields about 3 milliseconds of throughput delay at the expense of lower loudness.

Ethernet connectivity is now standard, as is a new, easy to use PC remote control application that runs on Windows 2000 and XP and that can control many 8500s on a TCP/IP network. In addition, RS232 serial control and programmable contact-closure (GPI) control give you total freedom to interface the 8500 with your facility’s remote control in-frastructure, whatever it might be.

User interface improvements round out the package. Orban started with the 8400’s easy to use joystick, knob, and button navigation system and added a bright, active-matrix color LCD that makes it easier to program the 8500 from its front panel. The panel’s eye-catching new metallic blue styling makes the processor look as great in your rack as it sounds on the air.

Processing for HD Radio

The HD Radio system generates a digital carrier that shares a given station’s allocated bandwidth with the normal analog FM carrier. The receiver crossfades between the analog and digital channels to minimize the effect of RF dropouts. This scheme requires audio processing for the two channels to be closely matched in texture to ensure that the receiver’s crossfades are seamless.

Optimum peak limiting for the two channels is very different. The analog channel requires state-of-the-art preemphasis limiting to achieve competitive loudness and minimize preemphasis-induced high frequency loss. This usually implies use of sophisticated distortion-canceled clipping. The digital channel, on the other hand, has no preemphasis but is heavily bit-reduced with the HDC perceptual codec. The highest available rate is 96 kbps, while the “Tomorrow Radio” initiative calls for a pair of channels, whose combined bit rate is 96 kHz. This limited bit rate creates an entirely different set of requirements: the peak limiting must not use clipping because there is no bit budget available to encode clipping-induced distortion products. However, preemphasis limiting is unnecessary. The best technology for peak limiting the digital channel is therefore look-ahead limiting, which can perform very clean peak reduction on flat channels, but which is unsuitable for pre-emphasized channels unless it is used as one element in a sophisticated system that also includes distortion-canceled clipping (as in the 8500s analog FM limiter).

Orban’s solution to this dilemma is Optimod-FM 8500: a single box processor where AGC, stereo enhancement, equalization, and multiband compression/limiting are shared between the two channels. Because these elements are mainly responsible for the station’s signature sound texture, this ensures that the analog and digital channels will crossfade unobtrusively regardless of the processor’s settings—great news for stations that daypart their processing.

After this processing, the signal splits off into two paths for peak limiting. The analog FM path provides distortion-canceled clipping with intelligent distortion control, overshoot compensation, stereo encoding, and composite limiting using Orban’s patented “Half-Cosine Interpolation” algorithm. Meanwhile, the HD output receives low-IM look-ahead peak limiting that operates in parallel with the analog FM peak limiting. This look-ahead limiting is optimized to make the most of the limited bit-rate codecs used digital radio and netcasting channels. By eschewing any clipping, the HD processing prevents the codec from wasting precious bits encoding clipping distortion products, allowing the codec to use its entire bit budget to encode the desired program material.

The digital processing chain also allows the station to insert a high frequency shelving equalizer either before or after the look-ahead limiter. Inserted before, it can reduce codec artifacts caused by excessive brightness in the previous processing. (This brightness is frequently introduced to compensate for HF limiter-induced roll offs in the analog chain.) Inserted after, it can realize the same advantage and reduce codec-induced overshoot too. A separate “digital path” mixer for the various bands of the multiband processing provides an alternate means for determining audio texture and controlling codec artifacts. Fortunately, the Spectral Band Replication® technology used in the HDC codec is far more forgiving of bright-sounding program material than was the technology used in the first-generation iBiquity codec (PAC). This allows the user to adjust the digital channel’s audio texture far more freely in the quest for the “perfect sound.”

The 8500’s 64 kHz base sample rate allows it to provide up to 20 kHz audio bandwidth at its HD output. The HD bandwidth is user-settable between 15 and 20 kHz to optimize the processing for the codec employed in the digital chain. Many low bit rate codecs operate better when fed 15 kHz audio because this enables them to use their available bit bandwidth most efficiently. This is particularly true for low rates, like 32 kbps. However, at higher sample rates, full 20 kHz bandwidth provides the same bandwidth as typical source material, so the user may prefer to use it for these higher rates.

Auditioned directly, the 8500’s digital output sounds dramatically cleaner and more open than its FM output, particularly in the high frequencies—it’s obvious just how much the analog channel is handicapped by the standard 75 microsecond preemphasis curve, which compromises its high frequency headroom. Using program material, Orban have measured as much a 12 dB difference in favor of the digital channel at high frequencies! Even after the digital signal passes through the 96 kbps codec, a significant amount of this audible superiority remains—the HD Radio system really does provide noticeably better sound to the consumer.

The first-generation iBiquity exciter requires 44.1 kHz AES/EBU audio streams for both its analog-FM and digital inputs. The sample rates for both streams must be identical. This requires two AES/EBU outputs from a single-box processor, both of which can be locked to an external AES reference signal. Because the output sample rate on either or both of the 8500’s AES3 outputs can be locked to either the 8500’s sync reference input or to its AES3 input, the 8500 fully meets the requirements. Moreover, because of the 8500’s built-in 8-second delay on the analog-FM channel, it is possible (and usually desirable) to entirely bypass the analog-FM side of the iBiquity exciter and to use the 8500’s built-in stereo encoder and composite limiter to drive the analog FM exciter directly.

Technical Specification

Technical Specification

It is impossible to characterize the listening quality of even the simplest limiter or compressor based on specifications, because such specifications cannot adequately describe the crucial dynamic processes that occur under program conditions. Therefore, the only way to evaluate the sound of an audio processor meaningfully is by subjective listening tests.

Certain specifications are presented here to assure the engineer that they are reasonable, to help plan the installation, and make certain comparisons with other processing equipment.


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

Frequency Response:
(Bypass Mode; Analog Processing Chain): 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 pre-emphasized output.

Sample Rate:
64 kHz to 512 kHz, depending on processing being performed.

Output noise floor will depend upon how much gain the processor is set for (Limit Drive, AGC Drive, Two-Band Drive, and/or Multi-Band Drive), gating level, equalization, noise reduction, etc. It is primarily governed by the dynamic range of the A/D converter, which has a specified over-load-to-noise ratio of 110 dB. The dynamic range of the digital signal processing is 144 dB.

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 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.



Defeatable Analog FM Processing delay:
8.12 seconds (maximum), adjustable in one-sample increments at 64 kHz sample rate to allow the delays of the analog and digital paths in the HD Radio system to be matched at the receiver output.

Minimum Processing Delay:
Processing structure dependent. Typically 17 ms for normal latency 5-band, 13 ms for low-latency 5-band, 3 ms for ultra-low-latency 5-band, and 17 or 22 ms for 2-band, depending on crossover structure chosen.

Analog Audio Input


>10k ohms load impedance, electronically balanced .

Nominal Input Level:
Software adjustable from -4.0 to +13.0 dBu (VU).

Maximum Input Level:
+27 dBu.

No jumper selection available for 600 ohms. Through-hole pads are available on I/O module for user-installed 600 ohm termination.

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.

RFI filtered, with high-pass filter at 0.15 Hz.

Analog Audio Output

Stereo. Flat or pre-emphasized (at 50 microseconds or 75 microseconds), software-selectable.

Source Impedance:
50 ohms, electronically balanced and floating.

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

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

³ 90 dB unweighted (Bypass mode, de-emphasized, 20 Hz- 15 kHz bandwidth, referenced to 100% modulation).

< -70 dB, 20 Hz — 15 kHz.

< 0.01% THD (Bypass mode, de-emphasized) 20 Hz — 15 kHz bandwidth.

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.

RFI filtered.

Digital Audio Input

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

Sampling Rate:
32 kHz, 44.1 kHz, 48 kHz, 88.1 kHz, and 96 kHz automatically selected.

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

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

J.17 De-emphasis:

RFI filtered.

Digital Audio Outputs

Two outputs, each stereo per the AES3 standard. The outputs can be independently set to emit the analog FM processed signal, the digital radio processed signal, or the low-delay monitor signal. The FM processed signal can be configured in software as flat or pre-emphasized to the chosen processing pre-emphasis (50µs or 75µs). The digital radio processing chain receives the output of the multiband limiter and processes it through a look-ahead peak limiter that operates in parallel with the main FM peak limiting system. The DR and FM signals are always simultaneously available. Each output can apply J.17 pre-emphasis if desired.

Sample Rate:
Internal free running at 32 kHz, 44.1 kHz, 48 kHz, 88.1 kHz, or 96 kHz, selected in software. Can also be synced to the AES3 SYNC input or the AES3 digital input at 32 kHz, 44.1 kHz, 48 kHz, 88.1 kHz, and 96 kHz, as configured in software.

Word Length:
Software selected for 24, 20, 18, 16 or 14-bit resolution. Optionally, first-order highpass noise-shaped dither can be added; dither level is automatically adjusted appropriately for the word length.

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

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

RFI filtered.

Frequency Response (Digital Audio Output (from Digital Radio Processing Chain)):
For output sample rates of 44.1 kHz and above, the frequency response from input to DR-configured output is ±0.10 dB, 2.0 Hz – 20 kHz; flat or with J.17 pre-emphasis applied. The user may specify lowpass filtering to constrain the bandwidth to 15, 16, 17, 18, or 19 kHz.

Relative Time Delay between FM and HD Outputs: Depends on setting of analog processing channel delay line. Once set, this delay is constant regardless of processing preset in use.

Digital Sync Input

Used for synchronization of either or both AES3 signals to an external reference provided at this input.

Sampling Rate:
32 kHz, 44.1 kHz, 48 kHz, 88.1 kHz, and 96 kHz, automatically selected.

XLR-type, female, EMI-suppressed. Pin 1 chassis ground, Pins 2 and 3 transformer balanced and floating, 110 ohm impedance.

RFI filtered.

Composite Baseband Output

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

Source Impedance:
0 voltage source or 75 ohm, jumper-selectable. Single-ended, floating over chassis ground.

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

Maximum Output Level:
+12.0 dBu (8.72 Vpp).

Minimum Output Level:
-12 dBu (0.55 Vpp) for 0.5 dB adjustment resolution.

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

Pilot Stability:
19 kHz, ±0.5 Hz (10 degrees to 40 degrees C).

D/A Conversion:

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

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

Stereo Separation:
At 100% modulation = 3.5Vpp, > 60 dB, 30 Hz – 15 kHz. At 100% modulation = 1.0 – 8.0 Vpp, > 55 dB, 30 Hz – 15 kHz.

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

<= -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).

Pilot Protection:
-60 dB relative to 9% pilot injection, ±250 Hz (up to 2 dB composite limiting drive).

Subcarrier Protection (60-100 kHz):
>= 70 dB (referenced to 100% modulation; with up to 2 dB composite limiting drive; measured with 800 line FFT analyzer using “maximum peak hold” display).

57 kHz (RDS/RBDS) Protection:
-50 dB relative to 4% subcarrier injection, ±2.0 kHz (up to 2 dB composite processing drive).

Two BNC, floating over chassis ground, EMI suppressed.
Maximum Load Capacitance: 0.047µF (0 ohm source impedance). Maximum cable length of 100 feet / 30 meters RG-58A/U.

RFI filtered.

Subcarrier (SCA) Inputs

Subcarrier inputs sum into composite baseband outputs before digitally controlled composite attenuator.

>600 ohms

SCA Sensitivity (Both Inputs):
Variable from 220 mV pp to >10 V pp to produce 10% injection. Sensitivity is adjustable by an internal PC-board-mounted trim pot.

Two BNC, unbalanced and floating over chassis ground, EMI suppressed.

19 kHz Pilot Reference:
SCA2 input jack can be jumpered to provide a 19 kHz pilot reference output or to serve as a second SCA input.

Remote Computer Interface

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

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 Connectors:
RS-232 port (3) DB-9 male, EMI-suppressed. Serial Connector 1 uses PPP to provide for direct or modem connection to the 8500 PC Remote application. Serial Connector 2 supports communication to a computer or remote control system via simple ASCII commands for administration and recalling presets. Serial Connector 3 is reserved for future developments.

Ethernet Connector:
Female RJ45 connector for 10-100 Mbps networks using CAT5 cabling. Native rate is 100 Mbps. Provides for connection to the 8500 PC Remote application through either a network, or, using a crossover Ethernet cable, directly to a computer.

Ethernet Networking Standard:

Remote Control (GPI) Interface

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

6 – 15V AC or DC, momentary or continuous. 9VDC provided to facilitate use with contact closure.

DB-25 male, EMI-suppressed.

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

RFI filtered.


100-132 VAC or 200-264 VAC, switch-selected on the rear panel, 50-60 Hz, 50 VA.

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

Circuit ground is independent of chassis ground’ can be isolated or connected with a rear panel switch.

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


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

0-95% RH, non-condensing.

Dimensions (W x H x D):
19″ x 5.75″ x 14.25″ / 48.3 cm x 14.61 cm x 36.2 cm. Three rack units high.

0-95% RH, non-condensing.

Tested according to Cenelec procedures. FCC Part 15 Class A device.

Shipping Weight:
19 lbs / 8.7 kg


Two Years, Parts and Service:
Subject to the limitations set forth in Orban’s Standard Warranty Agreement.

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