Delay lines or pedals offer a simple and convenient method of creating a sense of space around a sound or instrument, and can be used in many different and sometimes unexpected ways to alter the characteristics of a performance. The first delay lines were implemented using tape loops, where the audio signal was recorded onto a tape recorder in which the playback and record heads were offset so as to create a repeat of the audio signal. The length of the delay was adjusted either by using different lengths of tape, or by changing the speed of the machine. To create repeat echoes or feedback, the delayed signal was routed back into the machine. This method was used to great effect by avant-garde classical composers such as Karlheinz Stockhausen in his Musique Concrete. Audio engineers began to employ similar techniques in the 50s to enhance the sound of plate reverbs, and many rock n roll records of that era feature a short slapback echo on the lead vocal.
The invention of the Echoplex delay unit in 1959 opened up a new realm of sonic possibilities for many musicians, enabling them to create dense musical textures with ease. The Echoplex, and later in 1973, the widely used Roland Space Echo, were tape based delay lines, which sadly meant that after a period of time the sound quality became degraded, requiring the tape loop to be replaced and the heads to be cleaned. Eventually in the 70s, solid state delay lines became available. These were infinitely more durable and continued to be the method of choice until the 80s, when digital delays were introduced. However, many artists and engineers still seek out older tape based delay units for their retro sound quality, which differs greatly from solid state and again from digital units.