Back in the “old days,” producers and engineers created delay and echo effects using tape machines. A signal would be routed to a separate tape recorder (from the one being used to record the performance) that was set to monitor off its repro head. The slight amount of time that occurred between when the signal was presented and when it finally came off the repro head provided a delayed signal back to the main recording. The delay time could be adjusted by changing the speed of the tape machine used for the delay. Multiple echo repeats could be generated by routing the delayed signal back into the machine, and other effects, such as chorus and flanging, could be created by changing the speed of the machine while signals were passing through.
This technique became so popular that engineers began to devise ways to make the tape continuously loop on a machine so the tape would never “run “out.” Manufacturers eventually stepped in with dedicated tape echo products, such as the Echoplex and Roland’s Space Echo series. They had features and controls that were optimized for the intended purpose and used proprietary tapes that were already looped and in small cartridges. These machines were popular because they were easy to use and portable. Besides being great delay/echo units they were also many musician’s first foray into looping effects.
There were some downsides though. The recording quality wasn’t always great, depending upon the condition of the heads and the condition of the tape. Even on a perfectly tuned machine the quality would change (degrade) with each repeat because this involved playing the first echo out, recording it again, playing it, recording that signal again, etc. The degradation happened fairly quickly.
Eventually analog and digital devices were created for doing delay effects. They were cheaper, more reliable, and required virtually no maintenance. But by that time so many musicians and producers were accustomed to the tape delay “sound” that it was missed. Developers of electronic delays had to put in filters to roll off high frequencies as echoes repeated. In more recent years, modeling has allowed more accurate emulation of tape echo techniques.