One of the many challenges that face musicians who play and record in anything less than large rooms or halls is the lack of reverberation or room ambience. This is particularly true for people who play instruments in their homes or in studios where reverberation is so brief that it is almost non-existent. This really became a problem when the first Hammond organs became available because these could fit in any average room in a house in which noticeable reverberation is essentially completely lacking. From the days of the early Hammonds in the late 1930s on, and especially with the serious recording of music in general, devising artificial reverberation for music became necessary, and a number of different methods have been developed which do this quite successfully.
Before going any further, we need to define two words which are often used interchangeably but mean different things. The words are ECHO and REVERBERATION.
An echo is a distinct repetition of a sound occurring a short time after the original sound. If the original sound is very brief, such as a hand clap for example, there may be a short interval of complete silence before you hear a repetition of the hand clap. The repetition is caused by the reflection of the sound from a distant surface. In some unusual settings, you may hear a number of individual repeats of the original sound, each quieter than the preceding.
Most normal enclosures or rooms do not produce such a series of regularly-occurring multiple repeat echoes, however the effect is possible under domed ceilings if you stand under the center of the dome, and also in the arches of some stone-arch bridges, particularly if the arches are fairly narrow and large. A small arch that is perhaps twenty feet long and with a radius of ten feet will not give a very good repeat echo effect at all, whereas an archway that might be twelve feet long but with a radius of 60 feet will produce a very impressive series of multiple repeat echoes. A variation of this effect occurs in large outdoor sports arenas with PA systems where you hear sounds from remote speakers later than those from the closer ones.
Reverberation is a related effect but different. Reverberation is a very complex combination of a nearly infinite array of individual echoes coming from the many surfaces of various rooms and halls. Reverberation is present in just about all rooms, even tiny closets, but the effect in small rooms is so brief that we are usually not aware of it. However, in larger rooms and halls, for example, the reverberation lasts long enough that we are definitely aware of it. Because reverberation is a complex effect, it does not give any well-defined individual echoes or repetitions of a sound but rather just a prolongation of the sound after the sound source has ceased. Reverberation also tends to fade away gradually until you no longer hear it.
Reverberation time and quality are greatly influenced by the size of a particular room or hall, and also by the various materials and objects which comprise the room and its contents. If the walls are hard and smooth, like tile or marble, the reverberation will last for a much longer time than if the surfaces are carpeted or padded or covered with acoustical tile, in which case the reverberation will decay to inaudibility very quickly. In general, lower frequency sounds will reverberate for a longer time than higher frequency sounds, and this is likewise influenced by the presence or lack of hard smooth surfaces.
In the Hammond Organ article that is part of this series, we've already discussed the production of artificial reverberation by using coil springs. The production of artificial individual echoes, however is done somewhat differently. Actually, there are two main ways to do this. The first way is tape echo, and the second is by digital signal processing. Since tape echo was first, we should look at that way initially and then consider digital signal processing later.
As the name implies, tape echo is done by certain types of tape recorders. Not all tape recorders can produce tape echo. Most cassette tape decks will not do so. Commercial reel-to-reel decks which have separate recording and playback heads will produce tape echo if desired. It is hard to say when tape echo was first discovered. It seems to have been available by the 1950s, which would make sense as tape recording came into its own around that time. How tape echo was discovered was probably through a mistake in some recording studio where a recording engineer may have made an error in hooking up a tape deck and possibly some musician heard the resulting effect and liked it. As time went on, a number of companies produced special tape decks expressly for the purpose of producing single or multiple repeat echoes for music applications. So how exactly does a tape recorder produce a repeat echo effect?