When I look back over my broadcast career, I am amazed by how much the technology has changed over the years. Nothing has changed more than the way we play back pre-recorded materials.
Records: When I first started, all the music and syndicated programs were played back on records. Music came on records of two sizes, the 7 inch, 45 RPM and the 12 inch, 33 1/3 RPM disks. Syndicated programs came on 16 inch, 33 1/3 RPM disks. This meant the control rooms had to have at least one oversized turntable capable of holding those large disks. These turntables came with their own cabinets roughly the size of a modern clothes washer that housed the drive motors and pre-amplifiers. The weight of the platters helped maintain a steady speed because of their inertia, but that meant they took several revolutions to come up to speed. This meant that we had to slip queue the records we played so they would not "wow" up to speed at the beginning of the song.
Slip-queuing was an art. The disk jockey would place the needle on the edge of the record, turn on the turntable and listen for the beginning of the song on the queue speaker. When the first note was heard, we would stop the record by holding its edge, allowing the turntable to slip underneath. We would then gently back the record up about a quarter of a revolution and hold it with our finger tips until it was time to start the music. Then we would release the record, and turn up the "pot" or potentiometer at the same time. All the while we were doing this, we would be talking on the air or playing a jingle or commercial. It was a huge advance when instant-start turntables became available. They allowed us to queue up the record with the turntable stopped and simply start it when we were ready to play the song.
Tape: My first radio station had four reel-to-reel tape machines in it. Commercials, jingles and eventually syndicated programs were loaded on them. Again the process of cueing the tape was listening for the beginning of the recording by playing the tape through the queue system, stopping the tape when the first sound was heard, backing it up by hand a couple of inches and then starting the player when we were ready to play the recording. But it was a handful if you had a spot break that consisted of three or four commercials and a jingle. Our jingle package had its own machine, to the left of the audio console. I could find the start lever on that machine with my fingers without looking.
Tape technology had a big breakthrough in the mid 1960s, with the introduction of the cartridge player or cart machine. A cart was in essence the same construction as an 8 track machine of the 1970s, a continuous loop of tape wound on a spool contained in a plastic shell. The big difference is that it had only one audible program and would stop on a queue tone on a second program that was used for that purpose. The queue tone would stop the tape right in front of the recording. This meant that the DJ could just put the cart into the player and push start when ready for instant sound. This was much better. The blank carts usually came in several lengths, 40 and 70 seconds and then 2 1/2, 3 1/2 and 5 1/2 minute lengths, although I have seen them up to 15 minutes long. This meant you could "rotate" a series of commercials for one sponsor on a single cartridge each with its own queue stop tone. That feature that made life better for radio traffic managers and DJs alike. It reduced clutter in the control room. Ours typically had several hundred carts stuck in racks all around the space. (See the picture on the right labelled "On The Air At WCOS") Some were stored over the turntables, and that occasionally led to an on-air disaster if you dropped a cart onto record that was playing on the air.
None of this technology that was so ubiquitous back in the day exists in the modern radio control room. The one in the college station where I do a show today has three CD machines and a computer driven automation system at the DJs command. We are also only one of two stations in the entire city that still has turntables and a large collection of vinyl records in our library. A few of our DJs still play vinyl but besides the CD players, the audio source of choice is either a laptop or a MP3 player hooked up to the external audit source. When the other DJs there, mostly college aged folks, ask me about the old days and I describe slip cueing records to them they look at me like I have two heads. "No one can do that!" they exclaim. You know, maybe they're right, no one can - anymore. Oh MY!