TAPE ECHO
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 reverberation is essentially
completely lacking. From the days of the early Hammonds in the late 1930s
on, devising artificial reverberation for music became necessary, and a number
of different meth-ods have been developed which do this quite successfully.
Before going any further, we need to define
two words which are often used interchange-ably 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 com-bination 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?
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