Eventide BD 955 User manual

E^tide
the next step
iii
0
DIGITAL AUDIO
DELAY LINE
INSTRUCTION MANUAL
EVENTIDE INC..ONEALSANWAY . LITTLE FERRY, NEW JERSEY 07643 • 201-64M 200 .TWX: 710-991-8715

/
LIMITED WARRANTY
ALL EVENTIDE EQUIPMENT IS WARRANTED FOR A PERIOD OF ONE YEAR
n
from the date of purchase from Eventide or .f®® J®''.'
against defects In material or workmanship. In case of difficulty,
consult Eventide or your dealer for instructions.
This warranty does not apply to mechanical defects caused by use or rough
handling, or to damage caused by improper operation not in accordance with this
manual. Cause of defect is in the sole judgement of Eventide. There are no
other express or implied warranties, and no warranty of merchantability or
fitness for a particular purpose.
The warranty is voidable at Eventide's option under the following circumstances:
if the equipment Is connected to an improper voltage supply,
if the user makes unauthorized modifications of any type, if such
modifications are made, user agrees to pay for any time or parts
necessary to remove the modification before repair.
Eventide will under no circumstances be responsible for consequential damages
caused by failure of equipments of its manufacture, or for any other reason. Our
sole liability Is for repair or replacement of defective parts, under the terms
of the warranty.
SHIPPING
Equjpment should be returned. If possible. In the original packing container.
Loose cards must be wrapped In conductive foil (damage caused by failure to do this
will render the warranty void). If the original container Is not available, the
equipment must be packed to prevent damage from crushing or dropping. Damage caused
by Inadequate packing for service return Is not covered by warranty. We recommend
shipping via UPS rather than by US mail, and air freight If you are In a hurry.
If in our opinion the packing container Is inadequate for return shipment, we reserve
the right to supply a new container and charge for same.
The warranty covers return shipping in the continental US except Alaska. Return
shipments will not be insured unless the customer requests and agrees to pay for same,
if a more expensive form of shipment is requested, customer will be charged for same.
ALL RETURNED UNITS, IN OR OUT OF WARRANTY, MUST BE PREPAID TO OUR DOOR.
ALL RETURNED UNITS MUST BE ACCOMPANIED BY A COMPLETE TROUBLE REPORT, DETAILING
ALL THE PROBLEMS EXPERIENCED, CONDITIONS OF OPERATION, ETC.
FOREIGN SHIPMENTS
r
Foreign shipments must be returned fully prepaid, including Customs and brokerage
charges. Repaired equipment will be shipped all charges collect. A coiranerclal
invoice stating 'goods of US manufacture - being returned for repair' and giving a
fair market value of the unit should accompany the shipment, to save time and
expense. A copy of this invoice should also be mailed to Eventide.
REPLACEMENT OF PARTS UNDER WARRANTY will be done free of charge provided that
the defective parts and the warranty card for the unit are received by Eventide.
3/79
V

WARRANTY REGISTRATION FORM
MODEL BD955 DIGITAL DELAY LINE
SERIAL NUMBER
BANDWIDTH 7.5kHz () 15kHz ( )
DATE PURCHASED
YOUR COMPANY
ADDRESS
J)ELAY 6.4SEC ( ) 3.2SEC ( ) 1.6SEC ( )
STEREO MASTER ( ) SLAVE ( )
CITY/STATE/ZIP
STATION CALL LETTERS
STATION CALL LETTERS
AM ( ) FM ( )
AM ( ) FM ( )
CHIEF ENGINEER'S NAME
Person to whom data should be sent if
different from Chief Engineer
TITLE
Site where equipment will be located
if different from above
Is this site the studio? ( ) transmitter ( ) both ()
From whom did you purchase this delay line? FACTORY? () DISTRIBUTOR/REP? ()
If distributor, please give name and location__
How did you learn about this product?
Additional space for comments if desired. Thank you.
Please check if you would like information on other Eventide products:
H969 Harmonizer®( ) . H949 Harmonizer®( ) H910 Harmonizer®( )
SP2016 Signal Processor ( ) JJ193 Delay Line ( ) 283O Omnipressor®( )
RETURN FORM TO:
EVENTIDE INC..ONE ALSAN WAY . LITTLE FERRY, NEW JERSEY 07643. 201-641-1200 •

BD955 page 1.
TABLE OF CONTENTS
Warranty i
Warranty Form I i
Introduction 2
Specifications k
Front Panel Controls 5
Front Panel Indicators 8
Input Level Setting 3
Rear Panel Connectors 10
System Interconnection 11
Electronic Block Diagram 12
THEORY OF OPERATION:
Timing Oscillator 13
Timing Chain 13
Analog/Digital Converter 1A
Input Signal Conditioning 1A
Catch-Up Mode 16
Controlling the JUMP Command 16
JUMP Timing Diagram 18
Writing Data to the Memory 19
Stereo Interconnection 22
INTERNAL ADJUSTMENTS AND ALIGNMENT PROCEDURE:
Pause Level Control 23
Oscillator Frequency 23
Input Gain 23
Output Gain 23
A/D Converter Waveforms (diagram) 2k
Compander Card Top View (diagram) 2k
Oscillator Frequency Adjustment 25
Analog/Digital Converter Current Sink Adjustment 25
Input and Output Companders 25
Pause Level Control 25
A/B Offset Control Adjustment 26
"Full Gate" Input DIP Switch 26
DUMP Lamp Jumper 26
A/B Offset Pot Adjustment (diagram) 27
DIP Switch (diagram) 27
TROUBLESHOOTING (emergency and otherwise):
Timing Chain
Companders
Main Timing Diagram |?
Lengthening the Maximum Delay
SCHEMATICS: ^ ,
Timing and Control Logic I
Input Analog A/D, Output D/A Sheet 2a & 2b
Memory Addressing Logic and Readout Sheet 3
Memory Board and Array for BD955's with S/N B95757 & Below Sheet ka S kb
Memory Board for BD955's with S/N B9575B S Above Sheet kc
Power Supply and Chassis 1
Compander Card ^
APPENDIX:
Semiconductor and Internal Adjustment Drawing A-i
Diodes and Transistors used in the BD955 ^ ^ ^^"2
Integrated Circuits used In the BD955» with Plnout Diagrams A-3

BD955 page 2.
INTRODUCTION
The BD955 Broadcast Digital Delay Line is designed to enable the broadcast
licensee to meet his obligation to the public and to the regulatory author
ities to prevent obscene and/or libelous material from being transmitted over
his facilities. It does this by automatically delaying program material by
up to 6.4 seconds, thus allowing time for the monitoring operator to make the
decision as to whether the material being delayed fits in either category.
If it does, either of two methods may be used to ensure that material is not
aired. The first of these methods is standard: A taped jingle, censor s
beep, or announcement is placed on the air and the delay line output is tem
porarily cut off.. The second method is unique: newly developed electronic
circuitry (patent pending) allows the entire contents of the^ delay to be
"dumped", and the program resumed without interruption. Auxiliary circuitry
can be used if desired to prevent uncontrolled sources (such as telephone
callers) from being aired until the delay is again long enough to provide
protection.
Additional features of the delay line include the ability to generate short
delays for use in audio production applications, and to synchronize audio and
video in cases where video is transmitted via satellite and audio via land-
1 ine.
When compared to the traditional method of delay using tape loops, car
tridges, or even two recorders with the tape stretched between them, the
BD955 exhibits greater reliability, better and more consistent quality, no
requirement for operator attention, and, in cases where it is used continu
ally, lower monetary cost compared to that of a high quality tape machine
that would be otherwise unavailable. Of course, the unique variable delay
capabilities used in the "catch up" mode are mechanically unobtainable, as
are the short delay times so useful in production and synchronization appli
cations.
This instruction manual covers use, principles of operation, technical data,
and contains alignment and troubleshooting data should this be required. We
have also reprinted a copy of the "blurb sheet" for your convenience. May we
take this opportunity to thank you for purchasing this Eventide unit, and to
encourage you to return the warranty sheet. This will permit us to furnish
corrections and updates, as well as possible application notes and future
product announcements. If you have any questions or conments we should be
pleased to hear from you.

J
Eventide
the next step
BROADCAST DIGITAL
AUDIO DELAY LINE
MODEL BD955
THE DIGITAL BROADCAST DELAY LINE THAT BREAKS MURPHY'S LAW!
No tape loops that snap. No moving parts that break. No dead air.
DlOlTAl-
vBNTiae
The Eventide BD955 broadcast digital audio delay line offers memory
capacity to delay signals up to 6.4 seconds, it also incorporates a unique
"catch-up" feature, which eliminates the need for a taped jingle or
announcement.
EXCLUSIVE CATCH UP MODE
With the BD955, It's easy to get In and out of delay oper
ation. After pressing the DUMP button, an exclusive
mode of operation allows the program to continue In
real time, without the necessity for filling the delay
period with a jingle or announcement. Instead, as the
DUMP button Is depressed, the delay goes to zero, and
the obscenity Is deleted. Then, the delay Increases at a
variable rate while the program Is continuing, so that a
new delay margin for deletion Is built up. This catch-up
mode does not Introduce wow, and Is virtually unde-
tectable In operation. A front panel display shows. In
digital form (a progression of lighting LED's),how much
margin the announcer has. Until the delay is fully re
stored, he will have to be more alert, but the mode per
mits much faster resumption of the program, without
false Interruptions. The catch-up mode may be defeated
If normal delay operation Is required.
A VALUABLE PRODUCTION TOOL
When not being used as an editing delay, the BD955
delay line may be used as a production tool. Front panel
switches allow setting the delay from about 6.5 milli
seconds to the unit's maximum delay, a range useful for
many production effects. Including so-called 'doubling',
or giving the audible Illusion of multiple speakers,
singers or Instrumentalists.
FULL BANDWIDTH PERFORMANCE
A multl-LED level Indicator promotes proper level set
ting for maximum dynamic range. The standard unit
provides full 15 kHz frequency response. For applica
tions where wide band frequency response Is not need
ed, such as the delaying only of 'phone signals, the
user may opt for a 7.5 kHz model, at substantial cost
saving.
EVENTIDE INC.- ONE ALSAN WAY - LITTLE FERRY, NEW JERSEY 07643-201-641-1200-TWX: 710-991-8715

MODEL BD955 BROADCAST DIGITAL DELAY
specifications:
INPUT CHARACTERISTICS Impedance nominal 10 k, balanced, maximum
level + 24 dBm. Full dynamic range from
0 to +22 dBm levels. XLR female connectors.
OUTPUT CHARACTERISTICS
Electronically balanced, maximum level +22 dBm
Into 600 ohms. XLR male connector.
DISTORTION
Less than .3% at 1 kHz, reference level.
DYNAMIC RANGE Greater than 90 dB from clipping to noise floor.
DELAY
Memory capacity 3.2 or 6.4 seconds. Front panel
switch allows delay setting from about
6 ms to maximum.
FREQUENCY RESPONSE
15 kHz ± 1 dB or 7.5 kHz ± 1 dB
SIZE Requires 8.89 cm (31/2") x 48.26 cm (19") panel
space. Extends 31.75 cm (121/2") behind panel.
POWER REQUIREMENTS
115 VAC, 50^0 Hz, or 230 VAC, 50^0 Hz.
Nominal power dissipation 40 watts.
REMOTE CONTROL
Control of the DUMP switch and Indication of delay
margin provided on the rear panel connector. Relay
contact closure Indicates manual DUMP activation.
HOTESs * 7'/7e pricing of the BD955 Broadcast Digital Delay Line Is largely dependent upon the product of fre
quency response and delay. The customer Is urged to consider his requirement carefully,
it For other frequency response or delay, request quotation.
★ Once a unit has been purchased, It Is possible to alter the maximum delay time with little trouble. IT
IS Ifi/IPRACTICAL TO CHANGE THE FREQUENCY RESPONSE.
★ STEREO CONNECTION for two units Is available at a small extra charge. This allows either unit to be
used as mono backup.

FRONT PANEL CONTROLS
FUNCTION CONTROL
BD955 page 5-
FUNCTION
MAX—i /—OSC
MANUAL
SLAVE —
The FUNCTION control determines the mode of
operation of the B0955 delay unit. Its six
rotary positions operate as follows:
SLAVE: Configures the delay line to receive
delay change commands from another BD955. In
this mode, the cable provided with a mas
ter/slave combination must be connected to both
units. Both DUMP switches are connected in
parallel, and activating either is equivalent
■OSC PAUSE to pressing both simultaneously. After the de-
— PAUSE lay is reset by.the DUMP button, the delay of
both units will increase synchronously. IMPOR
TANT NOTE: SLAVE operation does not transfer
the MANUAL control setting from one unit to the
other. If it is desired to operate the master
unit in the MANUAL mode, the SLAVE must also be
in MANUAL, and both MANUAL DELAY controls
should be set identically.
MANUAL: In this mode, the MANUAL DELAY control
determines the delay setting of the unit. Re
fer to the MANUAL DELAY control description for
information on settings.
MAXimum: Setting the FUNCTION switch to this
position assures that the catchup rate will be
as fast as permitted by the internal timing.
This position is equivalent to the rate ob
tained by setting the unit to OSC with the
catchup rate at maximum, or to PAUSE operation
with no input signal.
oscillator: In this position, the catchup rate
is determined by an internal oscillator. The
speed of the oscillator is determined by the
CATCHUP RATE control. Because signal charac
teristics are not taken into account, operation
of the oscillator will be more obtrusive than
use of the PAUSE mode.
OSC PAUSE: This mode is a combination of the
oscillator and pause modes. It is used primar
ily to assure that catchup will occur even with
continuous program material. In operation,
catchup will occur at the oscillator rate if no
pauses occur, or faster (and less obtrusively)
if they do.
PAUSE: This mode causes the delay to increment
whenever the input signal drops below a certain
threshold. Thus, delay is increased during
syllabic pauses in speech or silent periods in
programming. Because these pauses occur during
low signal intervals, this mode is the least
obtrus ive.

BD955 page 6.
MANUAL DELAY CONTROL
MANUAL DELAY
16
SWITCH
0 31
When the FUNCTION switch Is In the MANUAL posi
tion, the delay Is determined by the MANUAL DE
LAY control. This Is a 32 position rotary
switch with no stop, so that It may be continu
ously rotated. No calibrations are Included on
the front panel because the delay Is not only a
function of the switch setting, but also of the
options (delay/frequency response) purchased.
The table below shows the approximate delay ob
tained at each switch setting.
Note three special positions:
Position 0 Is always zero delay.
Position 31 Is always maximum delay.
Post ion 12 Is the closest approximation to the
round-trip delay time by a video signal trans
mitted to a geosynchronous satellite. This
permits an audio signal transmitted by landline
to be delayed conveniently so that audio and
video may be synchronized.
' J
15KHZ UNITS
DELAY TIME
7.5KHZ UNITS
SETTING
6.4sEC 3.2SEC
1.6SEC
6.4SEC 3.2SEC
1.6SEC MAX. DELAY •
0
0
0 0
0
00
1
6.25
6.25 6.25 12.5 12.5
12.5 milliseconds
2
12.5
12.5
12.5
25
25 25
3
18.25
18.25 18.25
37.5 37.5
37.5
k
25 25 25
50
50 50
5
56 56 56
62
62
62
6
87 87 87
125
125
125 I
1
118
118 118
137 137
137
8
150 150
150
150
150
150
9
181 181
181
162
162
162
10
212
212
212
175
175
175
11
244
244 244
237
237
237 I-
12
275
275
275
250
250
250 1
13
306
306 306
262
262
262 1
14
387
362
337
375
325
325 1
15
469
418
369
437
387
337 p
16
525
450
375
450
400
300 1
17
631
506
431
562
462
412 1
18
737
587
487
675
575
425 P
19
894
694
545
837
637
487 !
20 1025
750
575
950
700
500 j
21
1.20
.881
.631
1.16
.81
.562 seconds 1
22
1.43 .987
.687
1.37
.975
.675 i
23
1.69
1.14
.768
1.64
1.08
.737 1
24 2.00
1.27
.825
1.90
1.20
25
2.36
1.45
.906
2.26
1.41
.862 ^
26
2.79
1.66
1.01 2.73
1.63
.975
27 3.29
1.89
1.12
3.23
1.89
28
3.87
2.15
1.20
3.80
2.10 1.15 A
29
4.58
2.46
1.33
4.51
2.41
1.26 ;
30
5.41
2.79
1.46
5.37
2.77
1.43 1
31
6.4
3.2
1.6
6.4
3.2
1.6 1

BD955 page 7.
DUMP
INPUI_LEVEL
FAST
CATCHUP RATE
SLOW
DUMP CONTROL: This momentary push button
switch Initiates the deletion of program mater
ial In the following manner:
1: When the DUMP switch Is depressed, the delay
Instantly goes to. zero. It will remain at zero
as long as the button Is held In. An Internal
relay closes when the switch Is pressed, and
opens about 1/2 second after the switch Is re
leased.
2: When the DUMP switch Is released, the delay
will Increase according to the setting of the
FUNCTION control.
3: Depressing the DUMP switch again before the
delay has reached maximum will cause the delay
to go to zero.
There Is a potential conflict between the MAN
UAL DELAY control and the DUMP switch: When
DUMP Is depressed, the delay will go to zero
regardless of the MANUAL DELAY setting. How
ever, when the DUMP switch Is released, the
delay will Immediately assume the MANUAL set
ting, If the FUNCTION switch Is In the MANUAL
position.
INPUT LEVEL: This control Is a continuously
variable attenuator which allows setting the
unit to optimum operating level. The section
on INPUT LEVEL SETTING gives criteria for pro
per adjustment of this control.
CATCHUP RATE: This control determines the rate
of delay Increase In the OSCIllator mode, and
the minimum rate of delay Increase In the OSC
PAUSE mode. When fully counterclockwise, the
catchup rate Is maximum. When the control Is
fully clockwise, the rate Is quite slow, and
several minutes are required to achieve full
delay.
POWER
N/OUT
POWER ON/OFF: Placing this switch In
position applies AC power to the delay
When power Is applied and the unit Is
the MANUAL DELAY control mode, the delay
Itlallzed to zero to prevent transients
by reading Invalid data from memory.
the ON
1 Ine.
not I n
Is In-
caused
LINE IN/OUT: Depressing this control applies
audio to the delay line, and enables Its out
put. When It Is OUT, there Is a DC path from
the Input to the output, and power need not be
appiled.

BD955 page 8.
FRONT PANEL INDICATORS
DELAY WARNING
oooooo
PRESENT-i NORMAL rPEAK
IN/OUT LAMP: This LED Is associated with the
IN/OUT switch. When this switch Is In the IN
position, the LED becomes IIlumlnated, signify
ing that the delay unit Is IN line.
DELAY WARNING Indicator group: These two color
LED's advise and warn the operator how much de
lay margin the delay unit has built up. When
the DUMP button Is depressed, all six Indica
tors turn red and flash periodically. This
signifies that the delay Is at or near zero and
It Is unsafe to place the phone caller on the
air. As the delay time Increases, the flashing
red Indication stops and the Indicators, start
ing at the left, turn green. The number of In
dicators which have turned green show graphic
ally how much time there Is to edit the Incom
ing program. One advantage of this Indicator
Is that It Is much easier to Interpret than a
digital readout. When one or two green lights
are on, the operator knows that he must be es
pecially alert; when they're all on, there's
plenty of time to react. This feature allows
resumption of program sooner than would other
wise be the case.
DUMP SWITCH LAMP: The Incandescent lamp In
this switch may be used In conjunction with the
DELAY WARNING Indicators: An Internal jumper
selects the drive point for this lamp so that
when a selected green LED comes on, so does the
DUMP lamp. This feature can be used to relieve
the operator of judgement. He can be told
"reactivate the 'phone when the light comes
back on". Alternatively, the voltage control
ling the lamp can be used to control the
Internal relay so that this relay disables the
telephone during the period Involved, thus pre
venting any possibility of human error.
SIGNAL LEVEL INDICATOR GROUP: These LED's
function as a "bar graph" display which depicts
peak audio Input levels. The leftmost "PRE
SENT" Indicator becomes Illuminated when a
small amount of signal Is present. The PEAK
Indicator comes on when the digital system Is
on the verge of Instantaneous cl ipping. The
section on INPUT LEVEL SETTING describes this
Indicator and the associated INPUT LEVEL con
trol .
\

1 BD955 page 9
INPUT LEVEL SETTING
The BD955 Digital Delay Line Is similar to amplifiers, equalizers, tape re
corders, transmitters, and virtually every other electronic device with the
possible exception of a piece of wire at absolute zero In that It has a
certain, limited, dynamic range. Dynamic range Is defined as the levels
between which operation of the device In question Is useful or acceptable.
As a practical matter, the range Is usually bounded on the high side by
excessive distortion, and the low side by excessive noise. In many equip
ments, a level Indicating device such as the familiar VU meter Is provided
to Indicate when the unit Is operating at the proper level. A tape record
er, for Instance, has a certain percentage of distortion at OVU, and this
percentage rapidly Increases as the signal level Increases. The noise
level Is some number of decibels below OVU, The number of decibels between
distortion and noise Is defined as "dynamic range".
Signal sources typically have a dynamic range much greater than that of
electronic devices. Likewise, the ear can hear a dynamic range much
greater than that of electronic devices. Since the electronic device Is
the limiting factor. It Is obviously a good Idea to set the operating level
of the delay l ine to take advantage of the maximum dynamic range of which
It Is capable. This Is the equivalent of making sure that the meter on a
tape recorder Is reading around OVU most of the time.
To enable accurate setting of Input level, a row of solid state Indicators
form a "bar graph" display underneath the INPUT LEVEL control. The lamps
are graduated In level so that, with any significant Input signal, the
leftmost becomes Illuminated, and, when the entire group Is on, a clipping
condition exists. With the INPUT LEVEL control fully clockwise, clipping
will occur at about +6 dbm at 1 KHz, This typically corresponds to approx
imately OVU In most facilities. Of course some margin above OVU Is re
quired and consequently the INPUT LEVEL control will normally be operated
between 12 and 3 o'clock.
The "ballistics" of the level display are such that It responds to Instan
taneous peaks. This fact, coupled with Internal circuitry designed to
reduce Internal system gain as Input level Increases ("companding"), makes
It desirable to operate the unit with the rightmost Indicator flashing per
iodically, Such Instantaneous peaks will generally be Inaudible, The
exception to this rule Is when the delay l ine Is connected In the audio
chain following compression and limiting: In this case, the INPUT LEVEL
should be set so that the second rightmost lamp Is flashing frequently, and
the rightmost virtually never.
As the dynamic range of the delay l ine Is about 90db, following this pro
cedure will Insure that It Is not the factor limiting performance of even
the widest dynamic range stations.

BD955 page 10.
REAR PANEL CONNECTORS
PONCrtOlJ
SUiTCH CWtP^O
> \
AC POWER CONNECTOR: This connector accepts an
Internationally approved "IEC" connector. The
line cord furnished with the unit Is for United
States standard 3 wire outlets. The line volt
age Is specified on the serial number plate,
and may be changed from 115VAC to 230\/AC by a
simple Internal wiring change.
FUSE HOLDER: The fuse In this holder Is In the
primary circuit of the power transformer. It
should be replaced only with a 1/2 amp slo bio
(l15VAC) or a 1/4 amp slo bio (230VAC).
OUTPUT CONNECTOR (3PIN XLR MALE): This Is the
audio output connector for the delay line. Re
fer to the specifications for levels and Imped
ances.
PIN 1 Is shield/chassis ground.
Pin 2 Is output -phase.
Pin 3 is output +phase.
INPUT CONNECTOR (3PIN XLR FEMALE): This Is the
audio Input connector for the delay line. Re
fer to the specifications for levels and Imped
ances.
Pin 1 Is shie-ld/chassis ground.
Pin 2 Is Input -phase.
Pin 3 is input +phase.
NOTE: For both input and output, the signal
phase Is arbitrary except at the very shortest
delays, as many wavelengths of any given signal
will be In the delay at any time. For phase
checking, therefore, the delay should be set at
0.
REMOTE CONNECTOR (8 PIN DIN FEMALE): This con
nector provides Input and output connections
for remote control of the DUMP switch and
external connection to the relay. See schem
atic below for connection.
EXTERNAL —
SWITCH CLOSURE
TO GROUND ACTI
VATES DUMP,
(pins 1^7.)
Pins 4 and 6 are spare
and may be used for
modifications.
NORMALLY CLOSED: pinsZandJ
NORMALLY OPEN: pins 3 and 5
INTERNAL RELAY CLOSES WHEN
DUMP SWITCH DEPRESSED
Remote Connector (as seen from
behi nd the uni t).
IMPORTANT NOTE: This drawing Is a REAR PHYSICAL VIEW of the plug. The numbers
molded on the plug should be Ignored as they are both illogical and do not cor
respond when supplied by different vendors.
When wiring the plug, connect your circuitry to the pins corresponding to the
physical position shown on this drawing.

BD955 page 11
SYSTEM INTERCONNECTION
The BD955 may be used in a straight delay mode, or one may take advantage of
the catch up mode. If it is being employed to replace an existing tape de
lay, it may be connected in the system identically to the tape unit, i.e.,
substitute the delay input and output connectors for the tape system input
and output connectors. In this mode, the delay should be set to maximum and
the DUMP switch never touched. Whatever control system currently exists may
then be used without modification.
If this is a new installation, and you wish to have the versatility of the
catch up mode and the use of fixed delay as well, there are several connec
tion schemes and control methods that may be used, and other commercial or
easily produced devices which will permit both.

BD955
BROADCAST
DELAY
LINE
ELECTRONIC
BLOCK
DIAGRAN
LOU-PASS
FILTER
COM
PRESSOR
VOLTAGE
TO
PULSE
I
HIGH-
SPEED
COUNTER
LEVEL
CONTROL
CONVERT
lOSHHz
D/A
CONVER
TER
MASTER
OSCIL
LATOR
DIVIDE
BY
16
TIMING
DIVIDERS
AND
ROM's
MEMORY
MATRIX
UP
TO
8
CARDS/20
RAM's
EACH
SAMPLE
RATE
,(DECR.)
20
BIT
COUNTER
BASE
ADDRESS
REGISTEHl
(ooooooo^
LEVEL
DISPUY
READ+256
WRITE
TT
MEMORY
BOARD
DECODE
AND
SELECT
,
I
REF
IN
REFER.
ENCE
GEN
:
1
ADDRESS
COMPU
TATION
ADDER
CHANNEL
A
SAMPLE
CHANNEL
B
SAMPLE
LEVEL
DETECTOR
FOR
PAUSE
JUMP
TIMING
CIRCUIT
INCREMENT
ON
JUMP
GATED
ADDER
DELAY
SET
COUNTER
F/P
DELAY
CONTROL
MANUAL
DEUY
PAUSE
PAU
iSE
+15
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THEORY OF OPERATION
The purpose of this section Is to describe In a fairly specific manner the
method by which the delay line operateso The various circuit sub-groups are
dealt with Individually, with reference to what each one does and how It does
It. To make this section of a manageable length, we assume that the reader Is
familiar with the Individual Integrated circuit "building blocks", and so will
describe the IC's place In the scheme of things rather than the operation of
the IC Itself. Pin connections and brief descriptions of the IC's will be
found at the end of this manual.
The circuitry of the BD955 Digital Delay Line Is contained on three printed
circuit assemblies. They are:
B955 Rev.- Main circuit and mother board
B951 Rev.- Random Access Memory board (B951 boards not used In units with
s/n 95758 & above)
303c Rev.- Compressor/Expander boards (See page 24)
The only electronic components not on these boards are the +15 volt DC regula
tor (mounted on the right side of the chassis), the +5 volt DC regulator,
(mounted on the rear of the chassis), and the power transformer. The various
Input, output, power, and control connectors are also located on the chassis.
Six schematic drawings reference these assemblies, and should be referred to as
an Integral part of this section.
The power supply (schematic sheet ^5) generates the regulated DC voltages re
quired by the remainder of the circuitry. Full-wave bridge rectifiers generate
raw DC at about +10\/ for the 5 volt supply, and at +/- 20 volts for the +15
regulated and -15 regulated supplies. The raw DC Is regulated by IC regula
tors, mounted on the chassis In the case of the +5 and +15 supplies, and on the
circuit board In the case of the -15 supply. Three silicon diodes In series
with the +15 supply provide the 12 volts required by the memory array, and a
zener diode/pnp transistor regulator provides the -5V (at very low current)
required as bias for the memories. The 5V Is employed by the digital logic as
a power supply and, after filtering, as a bias supply for the analog circuitry.
The + and - 15 volt supplies are used by the analog circuitry and output ampli
fiers.
TIMING OSCILLATOR:
IC33, sheet #2, a high-speed emitter-coupled oscillator provides basic timing
for the system. All clocks are derived from this signal by various dividers
and counters. This oscillator operates In the 100MHz range and there exists a
possibility for Interference if the delay line Is mounted In close proximity to
an FM tuner. If this should occur. It Is permissible to retune the oscillator
slightly without adverse effects on the rest of the unit. The output of the
oscillator Is applied to IC-34, a low power divide by I6 circuit, and to the
Input of the first counter In the analog to digital (A/D) converter.
TIMING CHAIN: The output of the divide by I6 counter Is connected to the syn
chronous timing generator consisting of IC's 47 through 52, and IC 54 (sheet
#1). IC's 47 and 50 divide the 6MHz output of IC34 by an additional factor of
16 (IC 47) times 10 (IC50). The outputs of the these two IC's are decoded Into
unique time slots by read-only-memories (ROM's) IC-48 and IC-5I, so that*events
can be Initiated at the proper times. The ROM's are asynchronous, and latches
IC-49 and IC-52 are used to "deglltch" the ROM outputs and apply the signals to
the rest of the system. IC-54 Is a flip-flop synchronously set and reset whose
period Is a few 100MHz cycles shorter than the maximum count of the A/D conver
ter, and whose output enables the A/D counter. This circuit effectively pre
vents overflow of the A/D. The Inter-relation of the timing signals produced
by this circuitry Is shown In the timing diagram.

BD355 page 14.
ANALOG/DIGITAL CONVERTER
The Analog to Digital converter changes the analog input signal into the dis
crete voltage levels required for storage in the digital memory. This is
accomplished by "sampling" the input signal at a fixed interval (determined
by the timing circuitry described above) and measuring the voltage of the
sample. The process is as follows: (refer to schematic sheet 2)
1: The input signal is applied to IC-^3 pin 8 at all times. IC-A3 is a quad
CMOS analog switch. During the "sample" interval, the .0039uF capacitor is
charged to the voltage of the input. When the sample pulse is turned off,
the capacitor is linearly discharged by a current sink. The discharge time
is a linear function of the initial voltage. Comparator IC-44 detects when
the voltage on the capacitor reaches 0 volts. IC-29 is a gate which enables
counter IC-32 during the period between the end of the sample pulse and the
time when the capacitor voltage reaches zero. This time is proportional to
the instantaneous voltage present on the capacitor at the end of the sample
pulse, and is measured by the counter chain IC-30, 31, and 32. Each success
ive stage of the counter divides the previous input by two. The maximum
count period, determined by IC-5^, is just nanoseconds less than that re
quired for the counter to reach a count of 2048, or 2 to the 11th power.
Thus the A/D converter is capable of resolving "11 bits", which corresponds
to an instantaneous dynamic range of about 66db. The outputs from- the
counter form the data word written into the memory under control of the tim
ing ci rcui try.
The front panel level indicator is operated directly from the A/D converter:
A 4 bit comparator, IC-28, compares the current value of the input signal
with the state of the 4 bit counter IC-27. if the input signal is greater,
then this new, larger value is strobed into the counter. If it is lower, the
counter remains as-is. Thus, these two IC's form an instantaneous peak
detector. The signal labelled "FLASH" is a slow speed clock which asynchron
ously decrements IC-27. This signal is orders of magnitude slower than the
peak detection function. If no peak comes along, however, the counter slowly
counts down. 10-26 is a ROM programmed to turn on various front panel LED's
in response to the state of the decrementing counter. An additional output
from the ROM inhibits the counter from going below zero and "wrapping
around", thus causing repeated cycling of the level indicator.
INPUT SIGNAL CONDITIONING
Before reaching the A/D converter, the input signal must be conditioned. The
conditioning includes compression which, with complementary expansion on the
output, greatly increases the DDL dynamic range, and filtering, which de
creases the ampl itude of high frequency signals which could cause spurious
responses from the DDL, known as "aliasing". The signal must also be offset
to +5VDC, so that the converter, which is inherently unipolar, can convert AC
signals. IC-46 comprises four operational amplifiers. The first section is
a differential amplifier which provides a balanced input and large input vol
tage range. Following the LEVEL control comes a gain stage and two three
pole low-pass filters to perform the anti-aliasing function. The compressor
card has two sections, a voltage-controlled-amplifier (VCA), and a level
detector. Unl ike the normal compressor, these sections operate indepen
dently.

BD955 page 15.
The input level Is measured and fed to the VCA In such a manner that, for
each 6db Increase In Input level, the gain of the VCA Is decreased by 3dB.
This provides a 2:1 compression ratio over a very wide dynamic range. The
two .luF capacitors and the resistors associated with this assembly are a
high-pass filter to remove sub-audible frequencies (such as turntable rum
ble) from the Input. The network between the compressor output and IC-A5
allows biasing of the signal to +5volts as required by the A/D.
Ignoring the Intervening delay circuitry temporarily, the output circuitry
comprises a D/A converter and the associated circuitry required to change
the digital numbers removed from the memory back to an audio signal. There
are additional complications Involved In this process, so we will discuss
the normal mode first, and then show what happens during the "catch-up"
mode.
/
IC's 35 and 36 are 6 bit latches which are strobed when each word becomes
available at the memory output. This datum Is applied to the Input of D/A
converter IC-37. This converter Is a special type called a "A-qUadrant
multiplying" D/A. This means that the output current or voltage (In this
case, current) Is the product of the digital word and a reference voltage
applied to the reference Input pin 17. Assume temporarily that the refer
ence Is fixed at -10 volts. As each word Is Input, It Is converted from a
current output to an offset bipolar voltage by IC-Al. The circuit con
stants are such that with a half scale digital Input, the output voltage Is
5 volts. As the Input varies between zero and full scale, the output
varies between 0 and +10V. (if the reference voltage Is decreased, the
offset remains the same but the full-scale amplitude decreases so that with
a reference of 0, the output remains at 5 volts.)
After the voltage Is available at the output of IC-Al, It Is sampled by
IC-A3, another analog switch Identical to the one used In the Input sam
pler. The output of this switch Is amplified by IC-A2 (pins 5,6,7) and
then filtered as done In the Input by a section of IC-A5. This filtered
signal Is expanded In a fashion complementary to the compression performed
at the Input. i.e., the gain of the VCA Is Increased by 6db for each 6db
Increase In the signal level. This "companding" operation reduces by a
factor of 2 the range of the signal going through the digital system and
would theoretically give a dynamic range of over 120db. Noise pickup and
other effects necessarily limit the Improvement, but It Is nonetheless
quite dramatic. The output of the expander Is applied to two sections of
iC-A5 which, together with their transistor buffers, comprise the output
amplifiers. These circuits are of Identical gain but opposite phase, so a
quasi "balanced" output Is available without response-degrading transform
ers. The peak to peak output level Is also doubled. The output Impedance
Is 300 ohms (150 ohms single ended), and suitable for driving any type of
load. The 10 ohm resistors In the collector circuit decouple the buffer
from the power supply and act as fuses if the output Is accidentally
shorted during test. (Shorting the output after the 150 ohm resistors Is
not harmful and can be endured indefinitely.)
U

BD355 page 16.
THE CATCH-UP MODE
A unique feature of the DDL is Its ability slowly and almost Inaudlbly to
Insert delay In live program so that time may be "caught up" without Inser
tion of artificial pauses or putting extraneous material on the air. The
key to this capability Is the ability of the random access memory to look
at various locations (delay times) upon instantaneous command. Each time a
catch-up command "JUMP" Is Issued, the output of the delay line Is dis
placed 256 samples, roughly 8 milliseconds, farther from the Input, thus
Increasing the delay by that amount. This must be done as unobtrusively as
possible. if It were done the obvious way, by reading In data at one rate
and reading It out at another, slower rate. It would result In a continuous
pitch shift which would abruptly terminate when the maximum delay Is
reached. This Is unacceptable, so the jump method operates as follows:
Assume you are looking at a signal at time A and that you want to listen at
time B, 8 milliseconds later: You can't simply switch times, because there
would be an audible splice. This Is the digital equivalent of splicing a
tape without an angled cut. The digital equivalent of the 45 degree angle
Is synthesized using the previously unmentloned circuitry of the D/A sec
tion.
The output of the memory Is actually sampled twice for each Input sample.
One sample reads the current value of the signal (sample A), and another
sample reads the value 256 samples later. Normally, the second sample
(sample B) Is Ignored by forcing the reference voltage on the D/A to be
zero during the time the B data Is In the latch. However, when the JUMP
command Is received, a counter, IC-40 Is enabled. This counter. In
conjunction with excluslve-OR gates IC's 38 and 39» forms a ramp generator
which controls the reference voltage on the DAC. Normally, during sample
A, the output Is -lOV, and 0 during sample B. As IC-40 Increments, the A
sample reference decreases to 0 and the B sample reference Increases to
-lOV. Each step of the ramp occupies one sample period, so that the tran
sition Is not abrupt. Note that another section of switching IC 43 samples
the B output. Both outputs are combined In IC-42 (pins 5,6,7).
The effect of all this Is that, when a JUMP command Is received, the ampli
tude of the current signal Is decreased and the amplitude of the delayed
signal Is simultaneously Increased. Because of the method of generation of
the reference voltage, the sum of the two amplitudes Is constant, thus pro
viding a smooth transition (splice). At the end of the ramp Interval, the
counter Is Instantaneously reset, the A output Incremented by 256 samples,
and the B output disabled. Thus the next sample (at full amplitude) Is
equivalent to what would have been the next B sample. The B output Is
meanwhile ready for another Increment.
CONTROLLING THE JUMP COMMAND
As smooth as the transition Is, It Is not Inaudible. There will usually be
some difference between the signals at the different times, and this will
show up as a combination of phase and amplitude modulation of the output
signal. This Is sometimes unavoidable, but there Is one further precaution
one can take: If the JUMP takes place during a period of no signal, then
there will be no splice "glitch".

BD955 page 17.
The major anticipated use for this unit Is for changing delay during talk
programmlngo Speech Is characterized by many pauses, both syllabic and dell-
berate, for thinking, effect, or whatevero By carefully tailoring circuit
time constants to these pauses, it is possible to add delay during natural
pauses In speech. Splices so occuring are Inaudible. The subjective effect,
during catch-up. Is that the speaker Is talking a bit more slowly, but there
Is no pitch change and no distortion Introduced! Additional catch-up modes
are provided: If music progratranlng. In which pauses are much less frequent.
Is contemplated, a variable rate oscillator can be used to Initiate the JUMP
command.
Because the pauses occur asynchronously with system timing, a bit of extra
logic Is required. Refer to sheet 1: When a JUMP command Is received
(NJREQ), a S-R flip-flop (lC-55) Is set. Assuming that a JUMP has not oc
curred too recently, this request Is passed through IC-53'(1>2,3) to IC-55
(8,9,10) which further qualifies the request by determining whether maximum
delay has yet been reached, signified by a logic low at the FULL gate output.
If It has not, IC-61 Is set. This flip-flop enables the B output strobe.
When a JUMP begins, the enable flip-flop, IC-5^ Is reset. This prevents
another jump from occurring too soon. If this were not done, the jumps could
be continuous and the output would be cut down to zero (catch-up rate same as
real time passage). The maximum rate Is thus determined by the Input pulses
to IC-59. Transition of the most significant bit on the ramp generator
signifies the end of the jump, which permits the process to begin at the
first jump request after the enable flop has been toggled.
The request rate Is determined by the function switch. If the NJREQ line Is
grounded (MAX position), then jumps occur as fast as they are enabled. A
relaxation oscillator (lC-60) can vary the rate substantially. In the OSC
mode, the capacitor on the Input of IC-60 Is slowly charged through the front
panel CATCHUP RATE control. When the capacitor reaches the threshold voltage
determined by the resistor network connected to pin 3, pin 6 goes low. Issu
ing the request. The digital circuitry then discharges the capacitor so that
after the jump It must re-charge before a new request can occur.
The jump on PAUSE circuit works as follows: IC-56 amplifies the A output
only. Its gain Is controlled by a circuit board mounted trimpot, R1. (This
adjustment can be changed to accommodate different talkers. IC's 57 and 58
form a dual threshold comparator. If the output from IC-56 crosses either
threshold, the capacitor on the Input to IC-59 Is discharged through one of
the diodes pointing to the comparator Input. If there Is a pause In the
Input signal, neither threshold Is crossed, and the capacitor slowly charges
through the resistor connected to +15V. When the capacitor voltage reaches
the threshold of IC 59, again determined by the resistor network, a jump
request Is Issued. In this case, the capacitor Is not discharged by the
digital circuitry, as we wish to take advantage of the pause as long as
possible. The final mode, "BOTH", Is a logical OR (a NAND gate Is perform
ing the OR function) of the PAUSE and OSC modes. In this case. If a pause
occurs, the oscillator remains Inactive, but If It doesn't, catch up Is
forced by the oscillator.
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