Product: Model 5121 Line/IFB Output Module

Overview

The Model 5121 Line/IFB Output Module is a compact, self-contained 2-channel module intended for use in custom broadcast, live-performance, and other specialized audio applications. The module provides broadcast and production talent cueing interfaces, specifically two line-level ("dry") and one IFB ("wet") outputs, in an easy-to-use yet technically sophisticated package. (Note that IFB is an acronym for Interrupted Fold Back, an arcane broadcast technical term meaning the cue signals sent to on-air talent or other technical support personnel.) The module's basic functions include selectable analog and digital audio inputs, input level and status LED indicators, two analog line-level outputs, and a 2-channel DC-biased ("wet") broadcast-standard IFB output. Remote monitoring capability is included to support advanced applications. Module operation requires only a source of analog or digital audio, along with an externally-provided source of 12 volts DC.

Applications for the Model 5121 include sports broadcasting booth packages, remote news gathering "fly-packs," stadium audio/video interface (I/O) locations, and other broadcast-infrastructure projects. The number of Model 5121 modules used in a project can vary widely—from one to dozens. In each case the Model 5121's performance will be completely "pro" with audio quality, reliability, and installation flexibility matching that of larger-scale audio consoles, matrix intercom systems, and stand-alone IFB systems. Typical applications will find either or both of the Model 5121's analog or digital inputs being interfaced with outputs provided by fiber-optic transport modules, audio/video routers, broadcast/production consoles, and matrix intercom systems.

The Model 5121's line-level outputs would typically be connected to battery-powered listen-only headphone amplifiers, amplified speakers, or inputs on broadcast media storage systems. In remote-broadcast applications these two outputs may be referred to as "dry" (no DC voltage present) IFB signals. The Model 5121's IFB output is directly compatible with listen-only portable IFB amplifiers, such as the Models 32A, 33A, or 34A from Studio Technologies, Inc. The 2-channel IFB output provides signal common on one pin, +28 volt DC power with superimposed analog audio on a second pin, and analog audio only on a third pin. This complies with a long-popular broadcast-standard implementation.

Model 5121 Line/IFB Output Modules do not include a mounting enclosure or chassis. They are intended for mounting in custom 19-inch rack panels, equipment boxes, broadcast furniture, "NEMA" I/O boxes, or other specialized enclosures. It is expected that integration firms will create applications that use Model 5121 modules as part of complete broadcast, production, corporate, and government solutions. Sophisticated users will be able to create "one-off" solutions to solve unique challenges.

Separate audio inputs are provided for interfacing with analog and digital audio sources. The two analog inputs are balanced (differential) and compatible with line-level signals. An unbalanced AES3 digital audio input allows the connection of two audio channels. A configuration DIP switch allows selection of the desired input signal. Two 7-segment LED meters provide the user with an indication of the input levels.

The Model 5121's audio performance is very good. Low-noise, wide dynamic-range circuitry ensures that the input audio quality is preserved. The audio from the digital audio input is routed to a high-performance digital-to-analog conversion (DAC) section that supports sample rates of up to 48 kHz with a bit depth of up to 24. The outputs of the analog inputs or DAC circuitry are routed to two line-level analog audio output sections. These provide the line-level, balanced (differential), ESD-protected, capacitor-coupled output signals.

The two signals from the selected audio input channels are also routed to the IFB circuitry. One channel is used to modulate the DC power source circuitry. The second channel is routed to a single-ended (unbalanced) line-driver circuit. The IFB power source circuitry provides a low-noise, current-limited source with a nominal 28 volt DC output. This is essentially identical to that created by "big time" broadcast IFB systems. Logic circuitry contained within the Model 5121 monitors the DC output voltage. Should a low-voltage/over-current condition be detected the DC output enters a protection mode. Once the fault condition is removed normal operation will again resume. An LED, located on the Model 5121's front panel, provides an indication of the IFB output's status. Note that for additional flexibility, the source impedance of both IFB output channels is 200 ohms, allowing intercom "beltpacks" to also serve as listen-only devices.

All audio inputs and outputs were carefully designed for use in permanent as well as field applications. Filtering on the analog audio inputs minimizes the chance that radio frequency (RF) energy will interfere with audio input sources. Other components were included to address ESD ("static") and DC over-voltage conditions The DC power input is protected from accidental polarity reversal.

The Model 5121 requires an external source of nominal 12 volts DC for operation. The acceptable input voltage range is 10 to 18 allowing a variety of power sources to be utilized. Power supply circuitry within the Model 5121 creates the voltages required for the analog audio, digital audio, and IFB circuitry.

Standard connectors are used throughout the Model 5121. Line-level and IFB output connections are made using 3-pin male XLR connectors. The two analog audio inputs use a 5-position, 0.1-inch "header" connector. A DIN 1.0/2.3 coaxial connector is used to interface with the digital audio input. The DC power input and data bus signals use a 4-position, 0.1-inch header. Low-cost IDC (insulation displacement) mating connectors allow simple interconnection with the analog audio inputs and DC/data signals.

For compliance with international broadcast audio level standards two versions of the Model 5121 are available. The Model 5121S supports SMPTE® audio levels where the analog audio reference level is +4 dBu and the digital audio reference level is –20 dBFS (SMPTE RP155). The Model 5121E supports applications that require European Broadcast Union (EBU) compliance with an analog audio reference level of 0 dBu and a digital audio reference level of –18 dBFS (EBU R68).