angle cut makes the splice 1/60 second long. If sound is cut at this same speed of 15 ips at a 90-degree
angle, there would be two possible reasons to hear noise: as explained previously, the possible
accumulation of iron dust in the space between the tape ends being read as noise by the play gap or the
difference in voltage between the bias voltage on each tape end; and the too rapid onset or cessation of
sound being heard as noise by the hearing system.
5.
Persistence of hearing. The persistence of hearing is another of the facts of hearing that has led
to the development of a very interesting technique in tape editing. Persistence of hearing is akin to
persistence of vision, which has made motion pictures possible, but the time it persists is not nearly as
long. It takes a definite time to hear sound as musical and that fact must be used in editing tape. Next it
will be explained how to use persistence of hearing in tape editing.
a. With normal hearing, at sound intensities commonly encountered, the persistence effect lasts
but a short time. Experience indicates it cannot be depended on for much longer than .03 to .06 seconds,
which is perfectly normal and, in fact, desirable. Music, as known, could not exist if persistence time
were much longer. How difficult it would be to understand anyone if the sounds of his speech persisted
in one's hearing and blended together in an incomprehensible mixture. Persistence time varies with
loudness and with the pitch of the sound. If the sound is more intense, persistence will be longer. The
effect on hearing of persistence may be used in editing, sometimes to avoid rerecording and still get a
natural sounding transition from one tape to another. For example, a person may wish to eliminate
commercial or other messages from a recorded program. In these programs, there is usually a managed
round of applause, followed by the message, which in turn is followed by the resuming program. If the
tape is cut immediately and spliced to the first sound of the resuming program materials, leaving no
space between, the applause will seem to blend into the following sound. In fact, when this operation is
properly performed, it will sound as though the applause continued for a split second underneath the
following sound. This can be called a "persistence blend." Of course, there are many conditions where
it may be difficult to create a natural sounding persistence blend.
b. All the factors discussed previously--mood, pace, level, background--effect the creation of
this kind of edited effect. It would not do, obviously, to cut from a laughing to a serious voice, or from
an extremely rapid pace to a very slow one of the same speaker. Moods must agree. For instance, if
laughter is to be persistence blended to a following voice, the latter must be in a jovial mood or be
saying something amusing. A good deal of practice in making these blends will show exactly what can
be done by means of persistence blending and what cannot be done.
6.
The editing tick. The editing tick is in the same category as persistence blending. It is useful
when there is either no time for dubbing (rerecording) or no equipment available for that purpose, and
when there is a noticeable difference between background sounds on two sections of tape that have to be
joined together. The insertion between two tapes of any slightly shocking sound that is in character--a
cough, a mike noise, a door slamming--provided it has been recorded in the same background as either
of the two
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