FAQs of the

• What is the bandwidth of the new satellite channels?

• What is the frequency response?

• What is the S/N ratio?

• How much crosstalk is there between sides of stereo pairs, particularly at high frequencies?

• How tight is the time/phase lock in stereo pairs?

• Does the SOSS computer need to be co-located with the demods?

• How will the new Audio Recording Automation (ARA) system interface with the hard disk audio storage and retrieval system I am planning to buy?

It is not a continuous data stream like SMPTE timecode. The internal clocks of SOSS computers are synchronized to network time through their connection to the 64,000 bit per second Downlink Services Channel (DSC) data stream, which also periodically sends time updates. While the Public Radio Satellite System operates in Eastern time, you can set up your SOSS computer with an offset that allows you to view system schedule in your *local* time.

At NPR Headquarters, when we installed the System Technical Center (STC), which has a modest amount of AES/EBU signals, we chose ADC DAB3-14MKIINS patch panels for the AES signals. These use Bantam size jacks with 48 jacks wide by 2 jacks high in two rack units. this was in late 1993. Ours are serial numbers 18, 19 and 20!

While we're on the subject, the AES signal also uses different cable (to wire your plant and racks) than does analog audio. To operate properly, it should be 110-ohm shielded twisted pair. When Harris Allied Systems installed the STC at NPR in 1993, they used Belden 9180 "digital audio cable".

The advice we got from ADC was NOT to have a "breakout board" on the wall where the AES signals would appear on punch blocks for cross-connecting. That adds jitter. We *do* have breakout blocks for the analog audio, though. Nothing in this message constitutes an endorsement of manufacturers or models by National Public Radio, Inc.

Unlike analog audio, a single pair of wires can carry stereo in this format. If you plan to begin to use AES/EBU digital audio signals in your radio station, you'll need to begin to think about audio in a whole new way.

Analog audio is not sampled or coded in any way, it's just a voltage that can be connected to the next device in the audio chain. AES/EBU audio, on the other hand, is divided into samples, which are combined with other data into frames. Each frame has a definite start and end point in time. In a 48 kHz sampled system such as ours, there are 48,000 frames per second. In order to be able to switch or cross-fade cleanly between two AES sources, they must be "in sync," with the start and end times of their frames matched exactly in time. If sync between AES frames is not in place at the time of the switch, an annoying "pop" will be heard when the result is decoded back to analog. Therefore, in order to build a successful broadcast plant using AES/EBU, you must have a master sync generator which aligns the AES frame outputs of all source devices. Some, but not all, RDAT recorder-players are equipped with (or can be equipped with at extra cost) a feature to allow playbacks to be synchronized with an external AES/EBU signal. This is sometimes called "genlocking." This signal may be a square wave "AES word clock" or it may be a "silent" AES/EBU signal. Expect to spend between $1,000 and $1,500 for an AES/EBU sync generator. The output of this generator, or of any other AES device, cannot be double-terminated if many devices need to receive its signal. So, you'll also need at least one AES/EBU distribution amplifier, costing $500 to $1,000. If you intend to pass AES/EBU signals through a routing switcher, you'll also want the switcher to cut between sources at frame boundaries, so the switcher would also need a sync source.

Some sources of AES/EBU audio cannot be synchronized to an external timing source because their timing is determined somewhere else, which could be thousands of miles away. A satellite demod is such a source. The AES/EBU frame timing at the output of a satellite demod is determined by the MUSICAM coded audio frames that are being received from the uplink site. Therefore, in order to allow clean switching between a demod and another source, or between two demods, another accessory device would be necessary: an AES/EBU re-framer, also known as a frame synchronizer. Expect to spend $1,200 to $2,050 per unit.

You cannot just terminate an AES/EBU circuit to "make silence" like you can in analog. You would need to switch to a source of "AES silence." By the same token, if you want a tone signal to align downstream levels, it would need to come from an AES tone generator which you might also want to synchronize.

If your audio plant also has analog equipment, you'll have additional concerns. If you want to switch between analog and digital sources, one of them will need to have the appropriate converter. Expect to spend $1,500 to $2,500 for each stereo channel of Analog-to-Digital (A/D) converter and $1,200 or $2,000 for each stereo channel of D/A. There are two modes for AES/EBU signals, "consumer" and "professional". When each of your ABR700 demods comes out of the ComStream box, the AES output will be set to "professional". This should be fine for any professional RDAT or hard disk audio storage devices you may have which follow the AES recommended practice. The user bits which are contained in the AES signals have already been set to a "universal" standard that will work with almost any professional device. A menu item on the ABR700 demod allows you to switch that demod to "consumer" for use with some brands of equipment. The user bits in the consumer mode are used for different purposes. We have also set them to be as universal as possible. (For example, in consumer mode, the Serial Copy Management System bits are set to "allow unlimited serial copies.") To order a copy of the" AES Recommended Practice for digital audio engineering -- Serial transmission format for linearly represented digital audio data, AES3-1992 (ANSI S4.40 1992)", please call the Audio Engineering Society at 212-661-8528. It's about $15.00 postpaid; Visa and Mastercard accepted.

• set up the computer and its peripherals to match station preferences;
• receive, view, copy, extract, sort, filter and print DACS messages;
• receive satellite transmission schedule;
• electronically mark which satellite transmissions they want to "capture" and to assign demods and tape recorders to capture them;
• type in local "events" that can be used to record feeds from other audio services or to automate their radio station.

In the new DACS system, each message will consist of the following:

• A "header" (the part with to: from: date:, plus new features like "keywords:";
• A text message or "body," which can only be sent and received as plain ASCII text characters, without boldface, italics or multiple font sizes;
• An optional "binary attachment" which can be a file of any size or format that can be meant to be read or used by any software program and any operating system.

Many e-mail systems allow file attachments to messages and the new DACS system will allow them, too. The person sending the DACS message (whether they are here at NPR or calling in on a modem)

will be able to specify and load in a file to be the binary attachment for each message they send. The attachment can be a file of any format, for example:

• it could be a word processing document in Microsoft Word for Macintosh format;
• it could be a word processing document in Word Perfect for DOS format;
• it could be a ".tif" graphic file that the receiving user can import into a drawing or graphics program;
• it could be a Microsoft Excel 3-D pie chart graphic;
• it could be a Lotus 1-2-3 spreadsheet;
• it could be a piece of software intended to be shared with the stations;
• it could be a copy of a database readable in dBase;
• it could be a file of simple text that a station can format and use in its own way later.
• it could be an audio or video file in the .wav or .au or .ra or .avi or another format.

You will be able to use the binary attachment feature to send out things like:

• art work promoting a program or series;
• art work intended for use in station program guides;
• format clocks for programs;
• charts and tables showing pricing, rights, availability or other aspects of programs;
• annotated drafts of contracts or other legal documents;
• electronic advertising slicks;
• etc.

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For the 128,000 bit per second mono channels, used for Standard Public Radio service, the RF bandwidth is 153.6 kHz, the audio bandwidth is 20 kHz.

The demods also support data rates of 192 and 64 kbit/sec which won't be part of Public Radio Standard Channel service. If an independent producer or distributor were to buy a channel of either of those sizes, and of the proper coding, the demod could receive them.

The RF bandwidth for 64,000 bits per second is 76.8 kHz.

The RF bandwidth for 192,000 bits per second is 230.4 kHz

Of the four digital bandwidths listed above, only one of them (the 128 kbit mono channel) is equivalent to an analog channel in the old Public Radio Satellite System. This analog channel occupies 180 kHz of RF bandwidth and has an audio bandwidth of 15 kHz. So, the digital system is slightly more spectrum-efficient.

In the old, analog system it was 50 Hz to 15 kHz, plus 0.4, minus 0.8 dB.

The analog figure is "better than 85 dB," which would be 10 dB below its own noise floor.

The analog figure is less than 13 degrees out to 15 kHz.

The RS-485 standard allows for a bus length of up to 4,000 feet and up to 64 devices (32 "talk" ports and 32 "listen" ports) can be connected. Devices on the bus can have addresses from 1 to 255 (address zero is reserved for the DACS alarm panel in our design).

The DACS/ARA PC will support at least five (5) such busses per radio station. Your chief engineer, at the time of installation -- and at any time after that -- may alter or configure the number of busses, which devices are on which busses and what their addresses and functions are. You can have one bus per "room" or "area" or you can put all ARA-controlled devices on a single bus -- your choice.

So, you CAN locate the DACS/ARA PC in the Operations Manager's office and still have the demods elsewhere.

There are many hard audio disk systems available today. Some of them can be controlled by a data link using a serial format, but those formats are generally proprietary. When the Satellite Operating Support System (SOSS) went thorough design, few hard disk systems were on the market and it was obvious that there wouldn't be a standard way of driving a serial port that could talk to them. So we designed for the lowest common denominator, isolated contact closures that can be used by virtually any analog reel-to-reel, RDAT or hard disk system. When choosing a hard disk system, if you want recordings to be started and stopped by the new SOSS, choose one that can accept contact closures as commands.

Expect some other manufacturers to follow suit.

Before choosing a hard disk storage system with MUSICAM inputs and outputs, ask the manufacturer the following questions:

1. What MUSICAM modes and data rates are supported? Possible modes are mono, discrete stereo and joint stereo? Possible data rates in the PRSS are 64, 128, 192 and 256 kb/sec. The Standard Channels will only be in 128 kb/sec mono or 256 kb/sec discrete stereo.
   
2. Do the beginnings and ends of individual recorded items on the hard disk occur at the boundaries between MUSICAM frames?
   
3. Can items be cued up, including back-cueing, to determine the start of the desired audio?
   
4. Does the system depend on the one-frame error concealment inherent in MUSICAM or are full error detection and correction provided?

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Yes. The OS/2 Schedule Editor and DACS Viewer applications can be networked. The contract we have with IBM requires them to test and to successfully implement networking using one combination of network environments which NPR must choose. (At last year's PRC, and shortly thereafter by DACS, we polled stations to see what LAN types were already in use. The most common was Novell Netware over twisted pair Ethernet.)

The main caveat we already know about: The ARA/DACS PC should not be used as a file server. Use another computer for that. The file server does NOT need to be running OS/2. Even if it's a peer-to-peer network.

Detailed instructions for HowToDoIt will be included in the documentation that's delivered with the DACS/ARA PC, software and training video. Here are the general concepts:

(1) There are two applications in the FISPO-delivered application suite that would be worthwhile to network. One is the DACS Viewer program which reads already-saved DACS messages from a disk drive or file server and displays them on the screen, and which sorts and prints messages, among other functions. The other is the Schedule Editor application, which allows you to see the System Schedule and to pick those transmissions you want to capture and to assign resources like demods and tape recorders to them, among other functions.

(2) To network either of these applications, you will need to make the OS/2 PC that FISPO delivers into a "node" on your LAN. This entails adding a Network Interface Card (NIC) to the PC. The card must be compatible with the PC's bus architecture and with the OS/2 operating system and with the type of "LAN medium" you use. A "LAN medium" is the wire or fiber optic cable or optical beam or radio frequency link that physically runs to each desktop or file server PC.

You'll also need a piece of software called a "requester" which is loaded into each PC that contains a NIC and which, in effect, runs the NIC. The requester must be compatible with the NIC card and with the operating system of the PC on which it is loaded. NIC cards can be bought new for as little as $75 per PC, but these cheap ones have a MAJOR drawback: You can't easily find requester software for them, which makes them useless. NIC cards in the $100 to $125 range tend to either be -- packaged with requester software or -- requester software for them comes with the LAN operating system software package that you buy when you set up the network in the first place or -- requester software for them is generally available for free from computer bulletin board systems or the Internet. For example, Novell Netware comes with requesters for most operating systems and NICs at no additional charge. OS/2 includes requesters for most of the major brand-name NIC cards like NE2000 and 3Com. IBM's LAN Requester is about $39 from Indelible Blue, Inc. DEC Pathworks requester software is $200 per client PC and we're not sure it supports OS/2.

(3) "Network operating systems" are software packages that are separate from the operating systems of the individual computers which they connect. Network operating systems usually go by brand names like:

• DEC Pathworks (which we don't think supports OS/2 requesters),
• Novell Netware (server software for 10-users, version 4.1, about $1680; 25-user 3.12 $2375)
• Novell Netware Lite (peer to peer, $69 per user)
• Artisoft LANtastic (about $109 per OS/2 user; OS/2 support is very proprietary),
• Banyan VINES,
• IBM ENTRY LAN Server,
• Appletalk, etc.

(4) Possible LAN media and topology combinations have non-branded names like:

• Thin Ethernet (coaxial),
• Thick Ethernet (coaxial),
• 10 Base T Ethernet (unshielded twisted pair),
• 100 Base T Ethernet (unshielded twisted pair),
• Fiber Distributed Data Interface (FDDI) (fiber optic cable),
• Copper Distributed Data Interface (CDDI) (the metallic wire version of FDDI),
• IBM Token Ring on shielded twisted pair, etc.

(5) You must buy another license for OS/2 for each client PC at which you want the DACS Viewer or Schedule Editor applications to run. The newest version of OS/2 is version 3, also known as "Warp", and it costs $70 to $90 per copy at discount computer stores and mail order houses.

One could kill several birds with one stone by purchasing IBM OS/2 3.0 CONNECT. This is a value-added version of OS/2 which has network support built in, including IBM LAN Server Requester, Novell's OS/2 Requester, and an OS/2 peer-to-peer network operating system. Street price is about $160 for the "full pack" version including WIN-OS2 support.

(6) You must copy the Schedule Editor and DACS Viewer applications either to each client PC or to the file server where each PC can read it. The latter is preferable. There are no additional licensing fees for this beyond what FISPO has already paid for.

(7) The client PCs also need to have NIC cards and requester software installed so that they also become LAN nodes. See (2) above.

(8) You must set up the ARA Schedule Editor in each client PC to use the network file server drive and path as its "working directory".

(9) When new or changed Schedule records are received from the Downlink Services Channel (DSC), they will appear immediately in the Editor in the DACS/ARA PC (if the Editor is running in that PC at the time). They will only appear in the other client PCs if the Editor is closed and is then re-launched.

(10) The DACS/ARA PC (the one with the ARTIC card in it) *must* be the one connected to the Downlink Services Channel data demod and the Electronic Serial Number (ESN) key. The DACS/ARA PC *must* be the one connected to the serial control bus(es) which control the real-time activities of the audio demods and tape recorders and any other connected devices.

(11) There is an Automation screen, called the Operator Action Display, which shows the automated schedule as it executes. It contains no editor and only a few controls that might be necessary for immediate attention by the technician on duty. This screen can only be on the DACS/ARA PC which contains the ARTIC card.

(12) If your station does not now have a LAN, you need to pick one, even if it is for this function only. You'll have to make the purchase of a LAN operating system (see sample brand names above), pick a network topology and install the wiring and connectors to reach each PC you want to serve. Costs are extremely variable for LAN operating systems. Some are priced for 4,000-user networks and some are for 10-user networks. You'll also need to purchase and set up the network file server from which the data will be shared. And the "concentrators" which talk to the individual wires connecting the PCs to a central point are, for example, $150 - $550 for twisted-pair Ethernet, depending on manufacturer and number of ports.

Typical concentrators have 12 to 16 ports for 12 to 16 PCs. NIC cards and LAN operating systems are no longer difficult to come by. Most computer dealers now sell networking products and services along with the computers. Many manufacturers add value to their product line by including third-party networking cards or software in the bundles they sell.

Mail order houses, office supply stores and computer discount supermarkets now stock networking products. Someone noticed Network Interface Cards (NICs) at the Price Club membership warehouse.

LANs and Connectivity - General

Derfler, Frank J, Jr., and Les Freed, Get a Grip on Network Cabling, Ziff Davis Press, 1993, ISBN: 1562760572, $29.95

Derfler, Frank J, Jr., and Les Freed, How Networks Work, Ziff Davis Press, 1993, ISBN: 15627 61293, $24.95

Derfler, Frank J. Jr., PC Magazine Guide to Linking LANs, Emeryville, CA: Ziff-Davis Press, ISBN: 1 56276 031 9

Derfler, Frank J. Jr., PC Magazine Guide to Connectivity, Emeryville, CA: Ziff-Davis Press, 1991, ISBN: 1 56276 047 5, $39.95

Gibbs, Mark, Absolute Beginners' Guide to Networking, Sam Publishing, 1993, ISBN: 06723 03264

Nunemacher, Greg, LAN Primer, 2nd edition, M&T Books, 1992, ISBN:15585-1287X, $26.95

Pournelle, Jerry and Michael Banks, Pournelle's PC Communications Bible, Redmond, WA: Microsoft Press, ISBN: 1 55615 393 7, $27.95

Rosch, Winn L., Winn L. Rosch Hardware Bible, New York: Brady/Prentice Hall, ISBN: 0 13 932260 4, $34.95

Artisoft LANtastic

Andrews, Jim, Inside LANtastic, Carmel, IN: New Riders Publishing, ISBN: 1 56205 072 9, $29.95

Derfler, Frank J. Jr. and Les Freed, PC Magazine Guide to LANtastic, Emeryville, CA: Ziff-Davis Press, ISBN: 1 56276 058 0, $19.95

Stoltz, Kevin, Inside LANtastic 5.0, 2nd edition, New Riders Publishing, 1993, ISBN: 15620 51938, $29.95

Novell Netware (Lite and Otherwise)

Freed, Less and Frank J. Derfler Jr., PC Magazine Guide to Using Netware, Emeryville, CA: Ziff-Davis Press, ISBN: 1 56276 022 X, $39.95

Leibing, Edward, Official Novell Netware Lite Handbook, Version 1.0 and 1.1, Novell Press/Sybex, 1992, ISBN: 0 7821 1095 9, $24.95

Neidermiller-Chaffins, Debra, Inside Novell Netware, Carmel, IN: New Riders Publishing, ISBN: 1 56205 022 2, $29.95

Neidermiller-Chaffins, Debra, Netware Training Guide: Managing Netware Systems, New Riders Publishing, 1993, ISBN: 15620-50699, $69.95

Sheldon, Tom, Novell Netware 4: The Complete Reference, Osborne/McGraw-Hill, 1993, ISBN: 00788-19091 , $39.95

Personal Computers - General

Moss, Julian, Upgrading, Maintaining and Servicing IBM PCs and Compatibles, San Marcos, CA: Microtrend Books, ISBN: 0 915 391 708, $29.95