Audio over IP, what is it, why should I care?

IP networks are the largest standardized data transfer networks worldwide.  These networks can be found in almost every business and home and are used for file transfer, storage, printing, etc.  The Internet Protocol over Ethernet (802.x) networks is widely understood and supported.  It is robust, inexpensive, well documented, readily deployed and nearly universal.  Many equipment manufactures such as Comrex, Telos, and Wheatstone have developed audio equipment that uses IP networks to transfer and route audio within and between facilities.

IP protocol stack
IP protocol stack

Audio enters the system via an analog to digital converter (A/D converter), often a sound card, at which point a computer program stores it as a file.  These files can be .wav, .mp3, .mp4, apt-X, or some other format.  Once the audio is converted to a digital data format, it is handled much the same way as any other digital data.

IP stands for “Internet Protocol,” which is a communications protocol for transmitting data between computers connected on area networks.  In conjuction with a transmission protocol, either TCP (Transmission Control Protocol) or UDP (User Datagram Protocol) IP forms what is known as the Internet Protocol Suit known as TCP/IP.  The Internet Protocol Suit contains four layers:

  1. Application layer – This is the protocol contains the end use data.  Examples of these would be HTTP, FTP, DCHP, SMTP, POP3, etc.  Telos Systems uses their own application called “Livewire” for their equipment.  Wheatstone uses “WHEATNET.”  Digigram uses “Ethersound.”   This is an important distinction.
  2. Transfer layer – This contains the TCP or UDP header information that contains such things as transmitting, receiving ports, checksum value for error checking, etc.  It is responsible for establishing a pathway through multiple IP networks, flow control, congestion routing, error checking and retransmission.  TCP allows for multiple IP packets to be strung together for transmission, increasing transfer rate and efficiency.
  3. Internet layer – This is responsible for transporting data packets across networks using unique addresses (IP addresses).
  4. Link Layer – Can also be called the physical layer, uses Ethernet (802.x), DSL, ISDN and other methods.  Physical layer also means things like network cards, sound cards, wiring, switches, and routers.

Advantages:

An IP network can be established to transmit data over almost any path length and across multiple link layer protocols.  Audio, converted to data can thus be transmitted around the world, reassembled and listened to with no degradation.  Broadband internet connections using cable, DSL, ISDN, or T-1 circuits can be pressed into service as STL’s, ICR’s, and TSL’s.  This translates to fast deployment; no STL coordination or licensing issues, no antennas to install if on a wired network.  Cost reductions are also realized when considering this technology over dedicated point-to-point TELCO T-1’s.  Additionally, license free spread spectrum radios that have either DS-1 or 10baseT Ethernet ports can be used, provided an interference free path is available.

IP audio within facilities can also be employed with some brands of consoles and soundcards, thus greatly reducing audio wiring and distribution systems and corresponding expenses.  As network speeds increase, file transfer speeds and capacity also increases.

Disadvantages:

Dissimilar protocols in application layer means a facility can’t plug a Barix box into a Telos Xtream IP and make it work.  There are likely hundreds of application layer protocols, most of which do not speak to each other.  At some point in the future, an IP audio standard, like the digital audio AES/EBU may appear, which will allow equipment cross connections.

Additionally, the quality of the physical layer can degrade performance over congested networks.  The installations must be carefully completed to realize the full bandwidth capacities of cables, patch panels, patch cords, etc.  Even something as little as stepping on a Category 6 cable during installation can degrade its high-end performance curve.  Cable should be adequately supported, not kinked, and not stretched (excessive pulling force) during installation.

TCP/IP reliability is another disadvantage over formats like ATM.  In a TCP/IP network, no central monitoring or performance check system is available.  TCP/IP is what could be called a “broadcast” protocol.  That is to say, it is sent out with a best effort delivery and no delivery confirmation.  Therefore, it is referred to as a connection-less protocol and in network architecture parlance, an unreliable network.  Lack of reliability allows any of these faults to occur; data corruption, lost data packets, duplicate arrival, out of order data packets.  That is not to say that is does not work, merely that there is no alarm generated if an IP network begins to loose data.  Of course the loss of data will effect the reconstruction of the audio.

Analog digital converter symbol
Analog digital converter symbol

Finally, latency can become an issue over longer paths.  Every A/D converter, Network Interface Card (NIC), cable, patch panel, router, etc has some latency in its circuitry.  These delays are additive and dependent on the length of the path and the number of devices in it.

Provided care is taken during design and installation, AOIP networks can work flawlessly.  Stocking adequate spare parts, things like ethernet switches, NICs, patch cables and a means to test wiring and network components is a requirement for AOIP facilities.

This is what you’ll get…

Back many, many years ago, in a city far away, I was driving down the road and I flipped one of “my” stations on the air.  The end of this song was playing:

The ending sounds an awful lot like a Moseley MRC-16 transmitter remote control’s return telemetry.  When I heard that on the air, my first response was “HOLY SH*T! The telemetry is on the main channel!”  A little voice in the back of my head said “That is not possible.  How is that possible?”  I grabbed the gigantic, then state of the art Motorola bag phone and dialed the studio hot line, just before I hit the  “send” button, the song faded out and the announcer came on back selling “Karma Police by Radiohead

Wow.  Radiohead?  Karma Police?  WTF?

I almost had a coronary.  When I got home, I tried explaining this all to my then girl friend, who didn’t get it.  Few do.  At the time, making such an error would be very bad form indeed and likely open the unfortunate party to all sorts of snickering and finger pointing at the next SBE meeting.

Crown D75 monitor amp goes terminal

Happened the other day, took out the monitor speakers too.  I am not sure how this happened, but the production director reported that the speakers began making very loud squeal.  Somebody finally thought to turn off the amp using the conveniently located on/off switch on the front panel.

Crown D75 audio board burned open resistor
Crown D75 audio board burned open resistor

The two watt resistor is burned open.  Also, this got so hot it burned a hole in the circuit board below it.  Truth be told, I think this amp was about 25 years old and due to be replaced when the new studios were built out.

I’ve seen these Crown amplifiers self destruct in the past.

Western Electric 212E vacuum tube

The company I work for is in the midst of cleaning out a studio location.  Most radio engineers are some form of pack rat.  I know I have been guilty of this myself, not wanting to throw something away because tomorrow, it might be needed.  That was carried out to the extreme at this location.  One of the things that I found in my clean out was a Western Electric 212E vacuum tube.

Western Electric 212E vacuum tube
Western Electric 212E vacuum tube

It is an impressive thing, measures about 12 1/2 inches tall, including the pins.  I am thinking this is pretty old, it probably came from a pre-WWII Western Electric AM transmitter.  This would make the most sense, as the station signed on in 1926 with 250 watts.  Back in the day,  Western Electric was the patent holder for AM technology.   In fact, there was some talk of suing General Electric for patent infringement after the airing of the world series by WJZ and WGY in 1922.  Parent company AT&T was working on radio modulation techniques to implement with their telephone system.

These tubes were used for audio amplification, according to the spec sheet, the plate could dissipate 275 watts.  Filament voltages is 14 volts at 6.2 amps, the plate voltage was 3,000 volts, maximum.  It is a tetrode.  The RF counterpart to this tube is the WE 308A.

From what I am to understand, these have not been made since 1960 or so.   I also understand there there is quite a cult following for this tube amongst Asian audiophiles.  There are several examples of extremely low distortion class A and AB amplifiers using this tube type.  Some prices on Ebay are in the $1,500 to $2,000 per tube range.  Unfortunately, I don’t think this one works anymore as there is a loose screw and little bits of what looks like control grid wire in the bottom of it.  It does light up with 12 volts on the filament, however.