A StudioComm for Surround system starts with the Model 77 Control Console. It's the system's "command center" and is designed to reside at an operator's location, allowing fingertip selection of all monitoring functions. Numerous LED indicators provide complete status information. A 4-digit numeric display indicates the post-fader monitor output level in real time. A major strength of the Model 77 is its ability to configure, under software control, many important operating parameters. Intended for secondary monitoring locations, the Model 71 Control Console is a compact user control surface. It provides three of the most basic functions: a rotary level control, dim on/off button, and reference level on/off button.

While many installations will use only one Model 77 Control Console, up to three additional Model 77 or Model 71 Control Consoles can also be connected. This provides multiple users with full control over a facility's monitor system. And to make installation simple, the Model 76D provides power for all connected Model 77 or Model 71 units.

The core of this StudioComm for Surround system is the Model 76D Central Controller. The one-rack-space unit contains circuitry that supports digital audio inputs, digital monitor outputs, processing, and the user interface. The Model 76D provides two surround (5.1) and three stereo digital audio inputs. These unbalanced digital inputs are AES3-compliant; sources of this type are ubiquitous in most post-production and broadcast environments. The inputs allow a sample rate of up to 192 kHz and a bit depth of up to 24 to be directly supported. Circuitry associated with one of the stereo inputs provides sample rate conversion (SRC) capability, allowing a wide range of digital audio sources to be monitored. Up to 340 milliseconds of input delay can be selected to compensate for processing delays in an associated video path. For flexibility, two delay values can be configured, allowing real-time selection as desired. A number of different signals can serve as the Model 76D's digital audio timing reference. For synchronization with a master timing reference a dedicated source of word clock, DARS (AES11), bi-level video, or tri-level video can be connected. Alternately, the L/R connection of the actively selected surround or stereo input source can serve as the timing reference.

A range of surround (5.1) and stereo digital monitor outputs are provided. The post-fader surround and stereo monitor outputs are intended for connection to monitor loudspeaker systems. The pre-fader surround monitor output can be used with metering systems that require signals that aren't impacted by level control or other monitoring functions. The stereo input C direct monitor output allows an installation to directly access the SRC capabilities.

For installation flexibility the monitor outputs can be configured for compatibility with equipment that requires balanced or unbalanced AES3 digital audio signals. When selected for balanced AES3 compatibility the output impedance is 110 ohms with a signal level of 5 volts peak-to-peak (Vpp). For unbalanced AES3 operation the impedance is 75 ohms and the level is 1 Vpp.

A sophisticated bass management function is integral to the Model 76D's design and can be enabled if desired. Note however that the bass management function is only supported at sample rates of 44.1, 48, 88.2, and 96 kHz. The overall goal of bass management is very simple: ensure that the entire audio bandwidth of all channels can be accurately monitored. Many loudspeaker systems have inherent low-frequency limitations, preventing a true picture of the source material from being presented. To overcome this, the low-frequency energy from the five surround and two stereo channels can be separated and then routed to the subwoofer loudspeaker. Several of the bass management functions can be configured to match the requirements of specific installations.

Great care was taken in designing the system's architecture, ensuring that the character of the audio input signals is preserved. All audio processing, including bass management, is performed in 32 bits using a high-speed field-programmable gate array (FPGA) integrated circuit.

The Model 76D occupies one space (1U) in a standard 19-inch rack. Digital audio sources are interfaced with the Model 76D using nine BNC connectors. A tenth BNC connector is used by the sync source. Digital monitor output signal connections are made using a 25-pin D-subminiature connector. One 9-pin D-subminiature connector is used to connect the Model 76D with up to four Model 77 or Model 71 Control Consoles. A second 9-pin "D-sub" connector is used to interface with remote control signals. AC mains power is connected directly to the Model 76D, with an acceptable range of 100 to 230 V, 50/60 Hz.

Additional Details

The Model 77 provides five buttons and associated LEDs for selection of the surround and stereo input sources to be monitored. While in most cases only one input source will be monitored at a time, stereo input C can be selected for simultaneous monitoring with one of the two surround or other two stereo inputs. This allows the two selected inputs to be combined ("summed").

It's interesting to note that while each of the two surround inputs has an LFE channel associated with it, the ".1" post-fader surround monitor output is designated as SUB (subwoofer), rather than LFE. This terminology was carefully selected to highlight the fact that this output channel may include more than just LFE content. The bass management function, if enabled, will redirect low-frequency energy from the main input channels, combing it with the LFE content before routing the sum to the subwoofer output.

The post-fader surround and stereo monitor output levels can be controlled by way of a large, easy-to-use rotary control. The control, actually a digital encoder, allows level selection in precise 0.5-dB steps. The auto mute all function causes the post-fader surround and stereo monitor output channels to automatically mute whenever the output level control reaches maximum attenuation. Using the reference level function, the post-fader surround and stereo monitor output levels can be set to a pre-configured value. This is provided for audio-with-picture applications that require a specific monitor output level. The reference level is easily configured by taking an electronic "snapshot" of the desired monitor output level. For operator confirmation a 4-digit LED readout can display the level of the post-fader surround and stereo monitor output channels. To match the needs of a facility, it can be configured to display either the attenuation level or the sound pressure level (SPL).

The dim function allows the post-fader surround and stereo monitor output levels to be reduced by a fixed dB amount. The dim level is configured from among four available values. A mute all function allows the post-fader surround and stereo monitor output channels to be simultaneously muted. The channel mute/solo section provides post-fader surround and stereo channel monitoring control, allowing a single channel to be muted or monitored. Multiple channels can also be simultaneously selected for muting or "soloing."

A special solo mode is also provided, called channel pop solo, which offers a unique aid in monitoring audio material. Channel pop solo allows the level of a single post-fader monitor output channel to be raised while the level of the other channels is reduced. This helps to emphasize the content on one channel without fully muting the others. Broadcast applications can benefit from the channel pop solo mode by allowing, for example, the center channel to be highlighted while still maintaining some level on the other channels. The amount of level increase—the "pop"—as well as the amount of attenuation can be configured to meet the needs of specific applications or users.

Two functions allow the input sources to be checked for level or phase inconsistencies. The surround to stereo downmix function is used to create a stereo signal from the selected surround (5.1) source. Key operating parameters in the surround to stereo downmix function can be configured to meet the requirements of an application. This can be especially useful when support for specific international broadcast standards is required. The stereo to mono downmix function allows audio on the left and right channels to be added (summed) and monitored on the center output channel. The two downmix functions can be simultaneously enabled, allowing a surround source to be checked for mono compatibility. The downmix functions always impact the post-fader surround and stereo monitor outputs. A configuration setting allows the pre-fader surround monitor output to be selected for pre- or post-downmix operation.

For flexibility, the StudioComm for Surround system is designed to easily integrate with equipment such as production intercom systems, on-air or recording tally signals, and audio consoles. Two remote-control inputs provide access to the mute all and dim functions. By providing access to these functions, talkback or slate activity from an audio console or other communications system can control the level of the post-fader surround and stereo monitor outputs.