TAPE ECHO
As is so often the case, a picture is worth lots of words. Here's a very simplified diagram of a tape deck and related items set up for tape echo production.
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Figure 1. Tape deck setup for echo production. A signal from a musical instrument enters the record amplifier as shown and then goes to the record head which places the signal on the tape. As the tape moves from left to right, after a short time interval, the tape passes under the playback head which picks up the signal from the tape. The signal next goes through the variable gain playback amplifier and then through a high pass filter. Because tape echo gives a distinct, repeating echo, the effect of this on bass notes can often mess up the rhythm or beat of the music.
The
high pass filter prevents low frequency (bass) tones from going either
to the speaker or to the record amplifier, whereas the higher notes of
the music such as the accompaniment and the melody do get through which
is the desired effect. The diagonal arrow through the high pass filter
means that it is adjustable, the exact setting depending on what is being
played and the musician's or recording engineer's choice. The playback
amplifier likewise has variable gain. If the speed of the tape is 7.5
inches per second, which is one of several standard speeds for many reel-to-reel
recorders, and the distance between the record and the playback head is
one inch, there will be a delay of 133 milliseconds from the time that
any signal is recorded on the tape until the delayed signal is heard at
the speaker. This is a little over a tenth of a second.
Therefore, any musical instrument sound
that gets recorded on the tape will be played back after 133 milliseconds.
This gives one distinct repeat of the original sound delayed a little
over a tenth of a second. Now, by feeding this first delayed signal back
into the record head, this will put a replica of the original signal back
onto the tape, which will itself be played back again after a delay of
another 133 milliseconds. Thus, a person listening to this would hear
first the original sound of the instrument and then two separate repetitions,
the first after 133 milliseconds, and the second after 266 milliseconds.
It is super important here to make sure that each subsequent repetition
of the signal on the tape has a lower volume than either the original
or the preceding repetition in order to produce a realistic trail of multiple
repeat echoes that fade away gradually.
Adjustment of the level of the delayed signal
which is re-recorded on the tape controls how many actual repetitions
the resulting echo effect will have. If the delayed signals are reduced
very slightly, there will be many repeats, whereas if the delayed signal
is reduced more, there may be only one repeat. If, by some chance, the
gain is set too high, the delayed repeat will be louder than the original
sound. Under this condition, the echo effect will quickly degrade to a
series of distorted noises that will bear no resemblance to the original
instrument sound. Obviously this is a condition which must be avoided.
If you are using a standard tape deck as
an echo producer, adjusting the playback level controls the number of
possible repeats, and changing the tape speed varies the delay time. Most
commercial reel-to-reel machines have tape speeds of 3.75, 7.5, 15, and
30 inches per second, although not all machines have all four of these
speeds available. In our above example, these would give delays of, respectively,
266, 133, 66.5, and 33.25 milliseconds. From personal experience I can
state that a delay of 33.25 milliseconds is too brief to be effective,
but the other three delay times are all useful for various effects.
Some manufacturers, however, developed tape
machines specifically for echo production, and some of these were quite
elaborate. On many of them, it was possible to move the playback head
closer or farther from the record head and thus get a wide range of delay
times within the capabilities of the machine. Still another advancement
was to include multiple playback heads which sent their outputs to different
speakers. In addition, these extra playback heads could also send their
signals back to the record head. The results from these machines were
excellent, producing a nice multi-channel stereo effect that approached
certain types of large room reverb patterns.
Not all tape decks can produce tape echo.
Many cassette decks and low-end reel-to-reel machines use a common record/playback
head and thus are useless for the echo effect. In order to produce tape
echo, there has to be a separate playback head and also a playback amplifier
which can operate independently of the record head and its amplifier.
Commercial reel-to-reel machines include these functionalities because
it is important for the recording engineer to be able to monitor the signal
recorded on the tape as the machine is recording so he can make any minor
tweaks as necessary while the recording is going on.
It is interesting to note that if you are
making a recording on a machine that is simultaneously functioning as
an echo producer, the recorded version on the tape will have the tape
echo included but with one difference. There will always be one fewer
repeat on the recorded version that you actually hear when making the
recording. The reason for this is that the first echo repeat that you
hear is actually the original recorded signal on the tape. If you had
the controls adjusted so that while recording you heard only one delayed
repeat, there would be no echo recorded on the tape.
There is also a related tape echo effect
that Ken Griffin used on a few of his recordings, and that is a type of
"plucked echo" effect. This is done by allowing just one repeat
and by not using either high pass filtering or any feedback to the record
head. The single repeat is played back at a considerably higher volume
than the original sound. The end result of this is a very soft initial
sound followed by a louder repetition after a short delay. This louder
delayed sound actually becomes the main signal for the music! On certain
types of music this gives a kind of plucked sound which is useful to achieve
a specific effect. If one is using a mixer and has the tape deck properly
connected to the system, it's also possible to have a few delayed repeats
follow the initial plucked effect. The drawback of doing this is that
for some, it is difficult to play accurately, because the musician hears
a considerably louder repetition of everything he plays which is delayed
by a little over a tenth of a second.
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