Early analog systems 

Early automation systems were electromechanical systems which used relays. Later systems were "computerized" only to the point of maintaining a schedule, and were limited to radio rather than TV. Music would be stored on reel-to-reel audio tape. Sub-audible tones on the tape marked the end of each song. The computer would simply rotate among the tape players until the computer's internal clock matched that of a scheduled event. When a scheduled event would be encountered, the computer would finish the currently-playing song and then execute the scheduled block of events. These events were usually advertisements, but could also include the station's top-of-hour station identification, news, or a bumper promoting the station or its other shows. At the end of the block, the rotation among tapes resumed.

Advertisements, jingles, and the top-of-hour station identification required by law were often on "carts". Short for cartridges, these were endless tapes similar to 8-track tapes, and looked nearly identical as well. Mechanical carousels would rotate the carts in and out of multiple tape players as dictated by the computer. Time announcements were provided by a pair of dedicated cart players, with the even minutes stored on one and the odd minutes on the other. This meant an announcement would always be ready to play, even if the minute was changing when the announcement was triggered. The system did require attention throughout the day to change reels as they ran out and reload carts. It became obsolete when a method was developed to automatically rewind and re-cue the reel tapes when they ran out, extending 'walk-away' time indefinitely.

Modern systems typically run on computer hard disk, where all of the music, jingles, advertisements, voice tracks, and other announcements are stored. The audio files would be either compressed or uncompressed, or often with only minimal compression as a compromise between file size and quality. For radio, these disks were usually in computers, sometimes running their own custom operating systems, but more often running as an application like Windows NT or later. Earlier text versions ran on MS-DOS, which was also quite stable due to its simplicity.  

The development MP3

The development of the audio compression format MPEG-1 Audio Layer 3, more commonly referred to as MP3,  provided the breakthrough in reducing traditionally large digital music files to much smaller compressed files without appreciable quality loss and thus being able to store vast quantities of MP3 encoded music on computer hard drive virtually signaling the end of large reel-to-reel tapes.  The MP3 audio-specific format  was designed by the Moving Picture Experts Group, a group formed by several teams of engineers at Fraunhofer IIS in Erlangen, Germany, AT&T-Bell Labs in Murray Hill, New Jersey, Thomson-Brandt Co.  and others.  It quickly became the de facto standard for digital audio compression and was approved as an standard in 1991.

Scheduling was an important advance in automation systems, allowing for exact timing. Some systems use GPS satellite receivers to obtain exact atomic time, for perfect synchronization with satellite-delivered programming. Automation systems are also more interactive than ever before with digital audio mixing consoles, and can even record from a telephone hybrid to play back an edited conversation with a telephone caller. This is part of a system's live-assist mode.

The use of automation software and voice tracks to replace live DJs is now the standard in radio broadcasting, done by many Internet radio and adult hits stations. Stations can even be voice-tracked from another city far away, now often delivering sound files over the Internet. In the U.S., this is a common practice under controversy for making radio more generic and artificial. Having local content is also touted as a way for traditional stations to compete with satellite radio, where there may be no radio personality on the air at all. The first PC hard-drive based automation system released to the public in America may have been Digital DJ, created by a Fort Worth, Texas company called The Management. 



History of Automation in Broadcasting
Full automation system computer controlled.
Cartridge Tape made by Scotch 3M  and a bulk cart eraser.  Each cart had to be erased before use.
Click for video explanation of "Cartridge Machines"
References:
  1. Wikipedia
  2. Fidelipac
  3. Scotch 3M
  4. International Tape Corp.
  5. Drake -Chenault  

Others stories and features
  1. Computers run the show at KEJC
  2. KHOP FM automation
  3. The history of Drake-Chenault
Computer automation software does it all today.
Broadcast automation equipment of the 60s and 70s was usually limited to "easy listening" music formats, because the hardware of the era wasn't capable of executing a tight, fast-paced pop music format. With easy listening, it was OK if there was some silence between songs; not so with Top 40! Top-40 needed tight segues, jingles, spots, time announce, weather, and other elements in rapid succession. The problem was how to make an automation system sound tight and quick?

The answer was developed by Drake-Chenault (D-C) by putting sub audible end-cues ("end of message (EOM's) on the program elements (music, jingles, etc) one second early, so the automation equipment had a "one second head start". This would compensate for the start-up delay of the reel-to-reel playback decks, and yield tight segues without any "wow-in". The next challenge was to figure out how to put those inaudible 25 Hz tones at the end of each song precisely one second early. The answer will explain why we used multi-track mastering decks in the D-C studios.

The original studios used Sony 4-track, 1/4 inch mastering decks. The master tapes were recorded at 7.5 ips. At the end of each song on the tape, a cue tone was recorded on a separate track. However, it wasn't the usual 25 Hz cue tone and it wasn't recorded one second early. It was a 1 kHz tone that was recorded in "real time", i.e., at the logical segue point for the song, not one second early. Because this tone was easily audible (through a small "cue" speaker) and it was on a separate track, it was easy for the studio engineer to place it at the proper segue point, tight against the end of the song. The cue tone could easily be re-recorded as many times as necessary until it's placement was appropriate to the song ending.

As time went by, D-Cs reel-to-reel programming clients began to diminish in numbers, eventually all of the tape clients were purchased from D-C by Broadcast Programming Inc. in Seattle, WA. The satellite programming clients remained, but they were eventually purchased by Jones, and the "original" Drake-Chenault organization pretty much disappeared.
Automated Equipment & Syndicated Music Formats

In the 1940s and 1950s, FM radio stations begin to gradually spring up all over the country, generally alongside a sister AM station. Most stations held their FM license by simulcasting the programming of the AM sister station.

In the 1960s the FCC introduced a rule that prohibited owners of AM and FM stations from simulcasting in an attempt to increase variety of programming and generate FM listenership. The FM audience share at that time was very small. Since the AM and FM stations aired the same programming, there was little reason to listen to FM. The rule targeted major markets first and had a "roll-out" period of several years with a less percentage of simulcasting allowed each year and smaller markets coming under the umbrella of the rule.

When station operators chose what format to air on the FM stations, one of the objectives was to not compete with the AM stations. During this time AM stations could target big audiences so you could categorize stations with broad definitions such as MOR, top 40 and country/western. So "counter-programming" the FM was simple. A young targeted Top 40 AM would likely target older on the FM and vice versa if the AM was an older targeted MOR station. Nearly every large market had a "progressive rock" album station, a forerunner to AOR, and a "beautiful" music station. Both approaches had some early success. The baby boomers were coming of age and gravitated to the better audio quality, fewer commercials and "hipness" of the free-form rock stations. Older FM listeners embraced the lush sounds and fewer commercials of beautiful music stations. Many offices and retail stores used the "beautiful" stations as free Muzak.

The station operators also wanted to be able to run the FM stations inexpensively. There wasn't the revenue from FM to support a "live" presentation with another staff of announcers. The result was the birth of automated equipment and the pre-recorded, syndicated format business.

Drake-Chenault Enterprises (originally American Independent Radio Inc.) was the primo radio syndication company that specialized in automation on FM radio stations. The company was founded in the late-1960s by radio programmer and deejay Bill Drake (19372008), and his business partner, Lester Eugene Chenault (19192010). Drake-Chenault was the predecessor of Jones Radio Networks with its syndicated satellite-delivered formats.
Samples of the various Drake-Chenault music formats heard on stations around the country and the world.