Studio Technologies Model 5121 Line/IFB Output Module (SMPTE)

Line/IFB Output Module - SMPTE-Compatible Audio Level Version

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" outputs and one powered "wet" IFB output, 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 analog and digital audio inputs, input level and status LED indicators, two analog line-level outputs, and a 2-channel powered "wet" broadcast-standard IFB output. Remote monitoring and control 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 audio inputs being interfaced with outputs provided by fiber-optic transport modules, audio/video routers, broadcast/production consoles, and matrix intercom systems. Only one of the audio inputs, analog or digital, will be used at any one time. No mixing of the signals will take place. While both physical inputs can be connected, by default the digital audio input will always take precedence. In the automatic selection mode the digital audio input will serve as the Model 5121's audio source should it be present and "locked" to the input circuitry. The analog audio input will be active whenever a digital audio signal is not present and "locked."

he 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 channel 1 audio on a second pin, and channel 2 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 and compatible with line-level signals. An unbalanced AES3 digital audio input allows the connection of two audio channels. By default, input source selection is automatic. If an AES3 digital audio source is connected it will have priority. 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 source connected by way of the digital audio input is routed to a high-performance digital-to-analog converter (DAC) section that supports sample rates of up to 48 kHz with a bit depth of up to 24. The two audio signals coming from the analog inputs or the DAC circuitry are routed to two line-level analog audio output sections. These provide the line-level, balanced, ESD-protected, capacitor-coupled output signals.

The two signals coming from the active audio input channels are also routed to the IFB circuitry. One channel is used to amplitude modulate the DC power source circuitry. The second channel is routed to a single-ended (unbalanced) line-driver circuit. The IFB 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 the IFB output channels is 200 ohms. This allows intercom user beltpacks to serve as listen-only devices as well as functioning as a small party-line intercom system.