Echo was almost certainly the earliest 'effect' used on electronic sounds. It is also the easiest to produce: all you need is a tape recorder with a record head offset by a few centimetres from the playback head. If you then record a sound onto the tape,you can replay it as a single echo a few fractions of a second later, with the delay determined by the tape speed and the distance between the heads. Later innovations included machines with multiple heads that produced a series of echoes,and tape loop systems that - if you wished - extended the number of echoes to infinity, each sounding muddier and less like the original sound than the previous. If you listen to the electronic music of the 1950s, you'll find it awash with tape echo, sometimes used to excellent effect, more often not.

The problem with tape echo was that it was neither convenient nor cheap to produce. A lighter and more affordable alternative arrived in the 1970s with the development of the bucket brigade device, or BBD. Although totally analogue in nature, a BBD takes a series of samples of the incoming audio, and allows you to tap these at various stages as they pass down a series of discrete steps through the device. BBDs made cheap electronic delay lines a commercial reality and, although they never sounded as good as their tape-based counterparts, solid state"echo units" soon became a staple of electronic music.

Although the maximum delay times available from BBD echo units tended to be rather short - of the order a few hundred milliseconds - they proved to be ideal for a wide range of electronic effects such as chorus, flanging and phasing,whereupon their often metallic sound could prove to be a benefit rather than a hindrance. The Analogue Systems RS-310 Reverb/Chorus is one such device and,unlike the stand-alone units developed in the '70s, this offers significant benefits such as voltage control of the delay time and voltage control of the mix between the unaffected and affected signals.

Of far higher fidelity, digital delay lines (DDLs) were also developed in the 1970s. Although rather clunky by today's standards, the earliest of these were unbelievably expensive, which is why they did not come to the attention of most musicians for another decade or so. To explain precisely how a digital delay line works would require a thorough treatise on sampling theory, and this manual is not the correct place for that. Nonetheless, it's not hard to grasp the basics...

A digital delay line is nothing more nor less than a specialised computer that samples an incoming signal and stores it in RAM. These samples are typically taken at a rate of 44,100 times per second, and stored with a resolution of 16- or 24- bits per sample. Once a sample is held, it can be read back at any time (or times) determined by the delay algorithm, until it is necessary to replace it with another incoming sample.The amount of time a sample can be stored is determined by the amount of RAM in the system.

If you can modulate the clock rate of a DDL and mix the affected signal with the original, you can create a much wider range of effects than just simple delays. As on their analogue counterparts, this is the method used to recreate sounds such as chorusing, flanging and phasing. However, few if any DDLs (other than the RS-390) have attempted to recreate the sound of a true tape delay, including the pitch shifts that are created when you change tape speed, and the others that occur as the recorded signal 'catches up' with the new speed. This is not surprising... it is a far from trivial task to do so. In contrast,the RS-390 is a true emulation of traditional tape echo, with all of that technology's strengths and weaknesses. It allows you to generate sounds and extreme effects that are not achievable elsewhere.