Digital wireline STLs
Moseley offers the Starlink SL9003T1. The heart of this system is the 3RU intelligent multiplexer into which daughter cards of various functions are installed. (An entire system is made up of two of these frames, of course, with sets of cards.) The cards for audio transport will accept analog input (+18dBu limit of headroom) or AES (or S/PDIF) via 110-ohm balanced XLR; sample rate 32, 44.1 or 48kHz with built-in SRC; and an auxiliary port for RS-232 that will run up to 9600 baud. If you want to accommodate HD Radio with multicast (or any of the other reasons to have a LAN extension at the transmitter) you would add the card that functions as an 802.3 Ethernet bridge; and you could build an off-premise telephone extension by adding the voice module data cards. The multiplexer frame can accommodate up to two T1 interfaces (one for redundancy), each of which has a built-in CSU. Management of the system is by a windows-based GUI that goes on a client computer; remote management is done via a built-in communications channel that operates over the link.
Probably the most well-known manufacturer of T-1 based equipment is Harris/Intraplex. The STL Plus (previous page) is a system made up of two frames into which daughter cards are installed. For an HD Radio application, this would consist of a PT353 (encoder card) and PR353 (decoder card) and a pair of DS64NC cards (making up the LAN bridge). The audio cards accept analog audio, or an AES data stream (selectable sample rate, with built-in SRC). Because the audio cards have both AES and analog inputs and outputs, the end-user can select the type of interface card that plugs in to the rear apron of the frame; analog only, digital only, or analog plus digital (XLR connectors all the way) are available as options. The plug-in interface card (known by Harris as module adaptors) for the DS64NC pair has an RJ-45 connector. Harris makes other card sets for OPX, and for data-reduced audio paths as well. Management of the system is via a serial connection, and remote management can be over the link using one of the ds0 timeslots.
Musicam USA makes a frame-based system as well, known as Team. The frame is 4RU and can accommodate up to 14 encoder or decoder modules in one frame. (Up to eight frames can be integrated to make up one system.) The frame can accept up to four T1s since each T1 interface card will connect up to two separate T1s. The audio modules accommodate analog and AES (via XLR connectors on the standard modules, or via D-connectors on the slim modules). MPEG layers 2 and 3, as well as Apt-X and Enhanced Apt-X are the options available for audio transport.
The local or remote units can be managed via Ethernet or RS-232, and have the ability to dynamically change the number of timeslots allocated for network communications on its LAN bridge, as well as the configuration of the audio cards (whether analog or AES is picked, and the audio coder in use).
One of APT's products that uses T1 for transport is the Worldnet Oslo. Like all the others discussed so far, the Oslo is a system made up of a mainframe, with plug-in modules that accomplish various functions. The frame can accommodate up to 12 audio channels in either direction: Individual audio modules come as two-channel duplex analog cards, four-channel analog simplex cards (one input and one complementary output card per system of course) and two-channel duplex cards with AES and analog inputs/outputs. Audio can be sent as linear PCM, or via compressed data codecs MPEG layer 2 or via Apt-X or Enhanced Apt-X. System management is by an Ethernet connection and a GUI called Worldnet NMS that lives on a client computer. I should note also that the mainframe will hold a redundant power supply.
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