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auditorium speaker system. They are however, picked off also applied to the three filter stages. These filters are quite
before the filter and used internally in the Perspecta de- sharp, producing an output only if the exact correspond-
coder unit to control the switching of the sound to the ing frequency is present. The three outputs are connected
three speaker systems. The frequency of these sub-audi- to detectors (not shown), which produce a voltage if the
ble tones are 30 Hertz (cycles per second) controlling the corresponding frequency is present. The detector's output
left speaker, 35 Hz. for centre channel and 40 Hz. for the voltage is used to tum on it's control gate, in the on posi-
right. tion, it sends the sound track audio to the following am-
plifier stage, and then to the speakers.
There is one shortcoming with the system. Because there
is only the one sound track available, when the sound is Because the filters are quite sharp, their bandwidth is only
switched from one speaker to another to move with the about+ or-2Hz, the speed of the projector is quite criti-
action on the screen, if there is a musical background, the cal. A one frame per second speed error can be sufficient
music will also follow the action. At first thought this might to create problems.
appear to be quite disconcerting, but it operation, it is barely
noticeable. There is no real reason why the Perspecta Directional
Sound system would not operate satisfactorily with 16mm
Although Perspecta saw its demise in the early 1960s, a films. However, there are no known l6mm Perspecta re-
company in England is making new "solid state" decod- leases. Films originally released with Perspecta Sound
ers for about 300 pounds. These units plug directly into a appear to have been reduced to 16mm without the Perspecta
slot on the latest Dolby processor units and have the added tones. In recent years, MGM and others have re-released
enhancement of providing rear speaker drive when all three some of their reClassic Cartoons' from the 1950s, these
Perspecta rechannels' are present. too are now being reprinted without the Perspecta tones
encoded.

Footnotes: I. Many of the well-known 1950s releases
were released in Perspecta versions, including most of the
Paramowlt Vista Vision releases as well as the Tom & Jerry
CinemaScope cartoons. Unfortunately, there appears to be
• • no authoritative listi·ng available.

2. The author would be pleased to hear from any
~ - one with 35mm Pers.pecta Sound films, even odd reels.

References:
.~ 1. International Projeclionist, early 1950s. 2. Titles of
• cartoon Daredevil Droopy (MGM, 1951) show "Perspecta
Sound". 3. Widescreen Movies by Robert E. Can & R.M.
Hayes. Publishers Mcfarland & Co.

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Perspecta Decoder Unit

T he signal flow through the Perspecta unit: The sound
from the operating projector is amplified in the pre ampli- Multi-<lireetional souncl
on a st~ruleirtT 9.P-ti;j,ft,'i,rk
fier and fed to the two filter stages. The high pass ftlter
rejects the low frequency Perspecta tones, but passes all of TJJh Is il! The •implt~, 1•eraumcnt Mtu.ad ~l'Nti'D 1h."1 co1'f'09 tJII tho
c:shibi1or·, s:tcnopJ•".oh; •out~d pro'blcuu -~nd h.', foUt co•p:ulblo
wi'h ~Dvco\iorul ,ound t:-'tlem,, Pro~tif'n (WOl"C'dutT$ remlllin 1hc:
the normal sound track audio through and feeds it to the Mmt:,lOO.
three control gates. In the normal or non-Perspecta mode, E1blblton "''th •tuCtOphonlc soond ca" 1whth ro l'm.p<:«CG Stetco•
pl1onie Sound t.y irM>t•llinc only un i.ntc:c,.tor uait_ dc•ian-c:n&l-
.Dtc:rcd by F:drt:hild. ':rhull'ft equfpj)C'd for ron,.c:nrion•l lOllbd nttd
the centre channel is always turned on and the sound is only 1ht tit~cJt~ mirnelc unh plua addhio:tl pc,.wer a.mpl.Wtu,
loulltf)eak«• ~ocl o mtlltiplo tauc fader.
conveyed to the centre amplifier and speaker system in
the normal way.
~iiciiiio··:ii~r:::::·
The low pass filter allows only the Perspecta low frequency
control tones to pass through. They are applied to the de-
~~ PICTURE SOUND D!VISIOH e WHIIUTONl !11, Nn¥ YORJ(
tector stage, which detennines if the film is in Perspecta,
and if is, the three control gates are switched into Perspecta
mode by the Perspecta on/off Jjne. The control tones are Promotional Advertising

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