Note: Descriptions are shown in the official language in which they were submitted.
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This application is a divisional application of
Canadian application Serial No. 616,517 filed March 4,
1993 which is a divisional application of Canadian
application Serial No. 612,739 filed September 25, 1989.
This invention relates to recording/reproducing machines and
more particularly to high speed duplicating machines,
especially--but not necessarily exclusively--for recording music
on any suitable medium.
The invention will find many uses; however, for convenience
of expression, the following specification may refer to the
making of audio tape cassettes. .Nevertheless, it should be
understood that the invention may be used to duplicate almost any
recorded information. For example, it may be desirable to
duplicate compact disks which are now coming into widespread use
as storage media for many things such as books, x-ray pictures,
graphics, data base information, and the like. The information
may be duplicated on any kind of media, such as tape, film,
compact disks, or the like. Further) the duplicator machine may
be used to store information in any suitable form which may be
selected by a computer. For example, an attorney who is going
into a trial may store information such as briefs, motions,
exhibits, and the like, which may be called up during the trial
by typing an address into a computer. Therefore, in the
following specification, the references to "audio tape cassettes"
are to be constructed broadly enough to cover all of these source
or program materials and recording media.
More particularly, this invention pertains to a high-speed
duplication of recorded material. This recorded material may be
music, voice, computer software or any other suitable material
that may be produced at high speeds and in multiple quantities.
An example of a product recorded by the inventive system could be
an album recorded on a magnetic tape cassette that is offered for
sale in retail record stores. These tapes need to be produced in
very large quantities in order to meet consumer demands.
1
The production problem is that cassette tanPC rannnt ~e 1 ~ ~ ~ s z
reliably run at very high speeds while the tape is in the
cassette shell. Therefore, it is customary to record the
magnetic tape before it is placed into the cassette shell. For
this and other reasons, the cassette tape is manufactured and
sold on a large tape reel, called a ~pancakea, which often
contains enough tape to fill twenty to thirty cassettes;
therefore, many copies of the source material are recorded on the
pancake.
Most systems for recording cassettes use an endless loop of
master tape that is mounted on pulleys in order to go around and
around, once around the loop for each length of the original
program material, which is usually recorded in an analog form.
To prevent this loop from becoming tangled or broken, it is
generally placed in a holding bin with one end of the loop
coming out of the bin, going across the playback head, and then
returning into the bin. The problem with these bin systems is
that the tape can become tangled, broken, or worn out merely from
going around the loop, hundreds of times a day. Therefore, a
master tape loop often has to be replaced several times a day, to
prevent signal degradation as the oxide is scraped off by the
playback head.
Ideally, a system would run infinitely fast in order to
produce the greatest possible amount of product each day.
However, the speed is limited because the tape passing at high
speed across the playback head creates an air gap and tends to
ride on an air cushion between the tape and head. One approach
to solve this air gap problem is to use an elaborate system of
compressed air to press the tape against the playback head.
Unfortunately, the resulting pressure acting on the tape causes
even more oxide to be scraped off the tape during playback and
requires the tape loop to be replaced even more frequently than
it would have to be replaced at lower speeds.
Master tape equalization becomes a problem when different
jobs need to be run at different duplication ratios. If the
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slave recorder is to run at 32:1 (32 times real time), the master
tape needs to be recorded at one tape speed. Another master tape
is required if the recorder needs to run at 64:1, another for
80:1 and yet another for 128:1. This means that either four
different machines are required in this example; or, a
substantial set up time is required whenever the duplication
ratio is changed. The air gap or air cushion problems arise at
about 128:1: therefore, the prior art duplicating machines become
very exotic if the master tape needs to run at such high speeds.
Accordingly, an object of the invention is to provide new
and improved duplicating machines. In this connection, an object
is to provide magnetic tape duplicating machines which overcome
the above described drawbacks, and in particular machines which
provide master tapes with a longer life.
Another object of the invention is to eliminate the need to
run the master tape past the recording head every time that a
duplicate tape is made.
Still another object of the invention is to provide superior
fidelity in duplicated tapes. Here, an object is to eliminate
problems heretofore encountered when the duplication ratio is
changed.
In keeping with an aspect of the invention, these and
similar objects are accomplished by a system which uses a video
cassette as the master tape to permanently store the,library
master recorded material. A high speed tape drive is used to
read the library master from the tape of the video cassette and
into an electronic memory. Once the library master recorded
material has been read into an electronic memory, the video
cassette is removed from the machine and thereafter the machine
records directly from the electronic memory, making any suitable
number of duplicate recordings.
Since an electronic memory is used to duplicate the stored
library master material, there is no tape loop to tangle, break
or wear out. This use of the electronic memory also eliminates
the air gap problems associated with the higher tape speeds on
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l~4osz3
the master tape reader. Since the duplicated tape makes only one
pass across the recording head at high speed, the slight wear
caused by air pressure upon the back of the tape poses no
problem. Since all musical information is being recreated from
an electronic memory, master tape equalization is not a problem.
In fact, the recreated master material stored in the electronic
memory is exactly the same quality regardless of whether the
duplication ratio is 16:1 (16 times real time) or 128:1 or some
other ratio. This means that the duplication speed is only
limited by the speed capab~.lity of the slave cassettes which are
being recorded, without any concern for how the master tape was
originally recorded. Therefore, if at a future date, faster
recording slave cassettes become available, duplicate recordings
may be made without having to either re-master or re-record the
master tape.
once a library master tape has been created on a video
cassette, it can be stored almost indefinitely for future use.
The library master tape also stores all critical machine
parameters, so that a library master tape can be pulled off the
shelf and re-run to produce a duplicate tape without requiring
any critical operator setup being required.
Yamamoto et al. (U. S. Patent 4,355,338) describes a system
that converts an analog master tape into digital signals that are
stored on discs. These discs are then loaded into the slave
recording device which reproduces tape cassettes on the slave
tape recording device. The advantages of the Yamamoto et al.
system is mostly speed independence except that, with present
disc technology, it is only possible to produce a low to medium
duplication ratio which cannot serve the higher speeds, such as
80:1 and 128:1. A major disadvantage is that Yamamoto relies on
machinery with moving parts which will eventually wear out.
Newdoll et al. (U.S. Patent 4,410,917) has no provision for
storing the master library material on a removable medium for
archive purposes. This means that, in order to maintain quality,
the original master analog tape must be pre-recorded into memory
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for every job that is to be run, presumably at a speed
which is slower than the actual duplication speed. This
pre-recording process takes a long time and tends to
produce inconsistent results. This Newdoll et al patent
also uses a data compression technique that could
possibly be unusable on some types of cassette tape.
With other tape technology, the compression techniques
may limit the quality of the audio signal that can be
recorded on the cassette tape.
The inventive system is thought to be ideal
because, after the library master video cassette is
loaded into the production line unit, the slave tapes
can be duplicated again and again over an indefinite
time period with neither signal degradation nor operator
intervention. Anther advantage of the invention is the
very fast library master tape load time. Therefore, a
production line that has frequent changes of source
tapes is able to load a new 48-minute source tape in
under two minutes. In fact, the library master tape can
be read out of the video cassette faster than an
operator threads the reel-to-reel type of master tape
used on prior equipment of a similar type.
Since the invention system uses no data
compression, the duplication tapes have the highest
possible quality. Also, since the invention can use
over-sampled output converters, the machine speed may be
made a completely independent parameter so that the
duplication speed ratios can be changed at will.
In accordance with an embodiment of the
invention, a system for duplicating pre-recorded
material on magnetic tape comprising means for supplying
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source signals from the pre-recorded material at a first
rate, means for recording at least a portion of said
source signals on a master library medium at said first
rate, means for generating digital signals from said
master library medium by playing back at least a portion
of said master library medium at a second rate, said
second rate being higher than said first rate, means for
electronically storing said digital signals from said
master library medium, and means for making a plurality
of duplicate recordings from said stored digital signals
at a third rate, said third rate being higher than said
second rate, wherein said duplicate making means
comprises means for converting the information
reproduced from said electronically stored signals from
digital to analog signals prior to making said duplicate
recordings.
A preferred embodiment of the invention is
shown in the attached drawings wherein:
FIG. 1 is a block diagram showing the
2o principles of the invention in a library master
recording system;
FIG. 2 is a block diagram of a buffer data
storage circuit for recording library masters;
FIG. 3 is a data storage controller for the
library master recorder;
FIG. 4 is a schematic circuit diagram showing
an electronic memory array for recording either a
library master or a duplicate tape;
,s
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FIG. 5 shows a block diagram of a control circuit which may
be applied to recorders for making either a master library or
duplicate tape:
FIG. 6 is a block diagram of an interface translator:
FIG. 7 is a block diagram of an analog-to-digital converter
which may be used to make a library master recording:
FIG. 8 is a first embodiment timing chart showing the
operation of an analog-to-digital sequence;
FIG. 9 is a second embodiment timing chart showing the
operation of another analog-to-digital sequence;
FIG. 10 is a timing chart showing the input/output timing of
an analog-to-digital converter:
FIG. 11 is a block diagram showing a control circuit of a
recorder for making duplicated tapes;
FIG. 12 is a block diagram of a circuit for playing back
data from electronic memory storage;
FIG. 13 is a block diagram which shows a circuit for
controlling an electronic memory data storage array:
FIG. 14 is a block diagram for a digital-to-analog
converter;
FIG. 15 is a graph showing the frequency response curve of
the inventive system:
FIG. 16 is a digital-to-analog converter for calculating a
higher quality analog curve:
FIG. 17 is a graph explaining the response characteristics
of the digital-to-analog converter of FIG. 16: and
FIG. 18 is a timing chart for the converter of FIG. 16.
For most purposes--and especially for descriptive purposes--
the inventive system may be split into two machines, one machine
being used to translate program source material into a library
master tape format and the~other being used to duplicate tapes
from the master tape. However, it does not necessarily follow
that a single machine cannot be used to perform both functions.
Quite the contrary, for some small scale uses, such as in a
retail record store, a single machine may be preferred.
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13406~~
The program source translation unit for making library
master recordings (FIG. 1) can accept signals from either an
analog source (a microphone, tape machine, phonograph or the
like) or a standard digital interface source (Digital Tape,
compact disk, or DAT). One great advantage of the inventive
system is its ability to directly transfer a digital tape used
for making a compact disc or the compact disc itself as a source
of material without having to convert from digital-to-analog and
back to digital. This gives the duplicated cassette a quality
which is as high as it would be if it were recorded directly from
the original digital source tape kith no degradation of sound
resulting from the various conversions that would otherwise be
necessary. The other half of the system (FIG. 11) is a control
circuit used for making duplicate recordings of slave tapes.
This unit may directly replace the present recording units, so
that the existing slave tape drive units may continue to be used.
Since the system may be split into two machines, the cost of
a production line unit may be reduced significantly because the
complex translation of analog-to-digital,. or digital-to-analog
can be done on a less expensive mastering unit. Also, since the
mastering process takes some time, it is advantageous not to tie
up an entire production line of valuable slave recorders in order
to do the mastering.
Figures 1-10 describe the mastering machine which is used to
create the library master tape by translating an output of an
analog source or digital source material into the format that is
stored first in an electronic memory and then from that storage
onto the library master tape.
Figures 11 through 18 describe the reproduction unit that
reads the library master tape into an electronic memory and then
writes the stored data at a higher speed through digital-to-
analog converters to one or more slave recording machines.
Figure 1 shows an overall block diagram of the mastering
machine with an analog-to-digital converter 34 and a digital
translator 40, which comprise alternate sources of signals with a
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l3~asz3
switch 41 for selecting therebetween. The operator controls
switch 41 to select between these and, perhaps, various other
types of source material and to indicate either a digital or
analog type of signal source. Then, the operator presses a
start button (not shown) at panel and control computer 30.
If an analog source is to be used, the control computer 30
starts the analog source transport 32 assuming that the source is
a recording. Then, the analog signals are sent through analog-
to-digital converter 34, there being one such converter for each
of the source channels. The information out of the analog-to-
digital converter 34 is in a parallel binary data format that is
sent for storage in an electronic memory forming the temporary
data block storage circuit 36.
If a digital source is used, the control computer starts
the digital source transport 38, again assuming that the source
is a recording. Then the digital information goes into the
digital translator 40 in a serial form. The digital translator
40 translates the serial digital information into two sets of
parallel binary data, one for the left channel and one for the
right channel of the duplicate recording. This parallel
information then goes into electronic storage in the temporary
data block storage 36.
Regardless of whether it begins with an analog or a digital
source, the data is stored in the electronic memory at an address
which is selected by the control computer 30. Also,. regardless
of whether it begins as analog or digital data, it is stored
until a full block of all data required for an entire selection
is ready to be recorded onto the library master tape.
When the block of data is ready to be sent, the control
computer 30 starts the library master tape drive transport and
data is sent over parallel data buses 42 to the tape drive 44.
Optionally, the tape drive could use an SCSI (Small Computer
Systems Interface) bus, in which case the data is sent in the
standard SCSI parallel data format. This process continues until
all of the source material is sent from the electronic storage in
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circuit 36 to the recorder 44. Then, the operator presses a stop
button. The control computer 30 ejects the tape from the library
master tape drive. In the preferred embodiment, the master tape
drive device is a video cassette recording means.
Figure 2 shows the details of the electronic buffer memory
or temporary data block storage circuit 36 for use in the
mastering machine of FIG. 1. Data comes in via bus 48 to a data
storage controller 47 within the buffer storage circuit. The
data is parallel binary data which is sent from either the data
translator 40 or the analog-to-digital converter 34. Each word
of data which is sent from the~translator 40 or the converter 34
is forwarded along with a storage address from controller 47 to
the memory array 50.
After the memory array 50 has received a full data block,
the control computer 30 sends write control codes via bus 52 to
the tape drive. The tape drive then returns a request for data
transmission via REQ wire 53 for starting the flow of data from
data storage controller 47. Responsive thereto, an address is
sent over wire 49 to the memory array 50. The data at that
location is read out over the data return lines 56, 58a, 58b and
sent out to the tape drive, either in parallel data form or as
SCSI data packets, depending on the type of interface that is
used on the tape drive. The data coming in via bus 48 from the
source 32 or 38 never stops coming until the operator issues a
stop command. However, the tape drive can write faster than the
source material comes in so that the tape drive is automatically
started and stopped to record such material without .interruption.
Figure 3 shows an expanded view of the data storage
controller 47 for controlling the data movement into and out of
the memory array 50. When the operator issues a start command,
the control computer 30 (FIG. 1) sets the storage base address in
the input base address generator 60. A signal on the input
request ("REQ"') line 62 indicates that data is available at the
data input lines. The data words are then latched, one by one,
in input latch circuit 64. As each data word is so latched, an
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address is generated by the input address generator 60. This
address is then sent along with the data and a write command via
buses 63, 65, 70 to the electronic memory array 50. After the
write step is done, the address is incremented and an acknowledge
"'ACK~ signal is returned on line 66 to tell the source translator
34 or 40 (FIG. 1) that the next data word can be accepted. Then,
the next set of data words is latched in the input latch 64.
The control processor 68 watches as blocks of data are
stored in memory array 50. When such a full block of data is
ready, the control processor 68 issues a write command to the
tape drive via the tape control bus 52. The control processor 68
then sets the base address in the output address generator 69 at
the beginning of the current data block. The tape drive uses the
output REQ conductor 67 to request data, word by word, from the
storage controller 68. As data words are requested, the output
address generator 69 sends an address and a read command over bus
71 to the electronic memory array 50. The data at the location
within memory array SO which is indicated by the address is then
latched into the output data latch 72 via bus 73.
The storage control processor 68 then pulses the ACK line 74
to inform the tape drive that the next available data is ready.
After an entire tape block has been written, the storage control
processor 68 stops the tape drive and waits until the next full
block is ready to write from memory. This process continues
until the operator issues a stop command.
Figure 4 shows the preferred electronic memory array 50
which may be used in either the mastering or the duplicating
machine. Each of the memory chips (such as 76) has an input, all
of which are connected in parallel by buses 63, 65, bus 65
carrying write commands. Likewise, each memory chip has an
output, all of which are connected in parallel by bus 73. The
entire array is addressed over a common address bus 70. Read
commands are given over common bus 71.
Thus, the electronic memory array 50 is a single and large
unitary array of memory chips 76, preferably with each of them
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large enough to store one million bits of information (1 Mbit
chips) or optionally four millions bits of information (4 t9~it
chips). These chips are manufactured by many companies
including Toshiba, Samsung, Oki, etc. The inventive system would
contain approximately 32-64 MegaBytes of memory, which translates
into 256-512 of the chips 76. The chips are organized with the
various memory areas selected when their addresses appear on the
address bus 70. When a write command is issued via bus 65, the
chips that are selected by the address on the address bus 70
store the information that is then present on the input data bus
63. When a read command is issued via bus 71, the chips 76 are
selected by addresses on the addzess bus 70 in order to retrieve
the information stored at that address and to present it to the
output data bus 73.
Figure 5 shows the control buses leading to the master
library recording machine or tape drive 78. It is here described
as the tape drive for making a master recording on a video
cassette. However, it could equally well be the tape drive for
making an audio cassette. One such-video tape drive is
manufactured by Honeywell and is known. as ~VLDS~ (Very Large Data
Store). It is used because it accepts a tremendously fast data
transfer rate. This is essential to the fast loading of the
duplication line audio data. The unit can be purchased with
either a Honeywell proprietary parallel data interface or
optionally with a SCSI interface port. The preferred embodiment
uses the SCSI port.
The storage control processor 68 (FIG. 3) may control the
tape transport via the tape command bus 52 to provide the
function commands including start; stop, record, play, search,
rewind, etc. After a write command is issued, the drive.requests
data from the storage controller 47. Then, data comes in either
through the SCSI ports 80 or the parallel interface 82, whichever
is used. For the master library recording, the data is recorded
on video tape cassettes, preferably in the VHS format.
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Figure 6 shows the details of the digital source translator
38 (FIG. 1) for the library mastering machine. This circuit
translates the serial digital information that is received from
the digital source device into parallel information that can be
used by the library mastering system.
In greater detail, a digital master machine or a compact
disc player can be fitted with an AES/EBU interface identified by
the Audio Engineering Society specification SPEC# AES3-1985.
This specification provides a serial data interface for digital
audio equipment, and is thought to be the standard port used by
most new compact disk and DAT machines. As this serial
information comes in from the digital source 38 (FIG. 1) via bus
84 (FIG. 6), the sync detector 86 looks for and finds the sync
bits in the data stream.
Once the sync bits are detected, the left and right channel
serial to parallel shift registers 88, 90 are clocked via wires
92 to take in and convert the data stream into parallel data.
After a full 16-bits of data are clocked out for left and right
channels, the sync detector 86 pulses the STB line 94 to inform
the storage control processor 68 that the output data is
available. Then, the storage control processor 68 receives both
channels of parallel data which are sent in a 16 bit format for
each channel. This interchange of data continues until the sync
detector 86 does not detect any more sync bits, which indicates
that the digital source has been stopped by the storage control
processor 68.
Figure 7 shows the detail of the analog-to-digital converter
34 (FIG. 1) for the library mastering machine. This circuit 34
converts the analog signals received from an analog source 32
into the digital information which is used internally within the
system. First, an analog balanced line 95 is used as an input so
that noise is reduced substantially and as much as possible.
This balanced signal is added together in the differential input
amplifier 96, a stage with no gain. Preferably, the amplifier 96
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may be one manufactured by the John Hardy Company, of Evanston
I1, where it is known as a Type 990"' operational amplifier.
The output of the differential amplifier 96 is fed into the
input gain adjust control, device 98. This gain adjustment
provides adjustments which accommodate different kinds of audio
equipment. The total input range of adjustments provides for a
peak as low as -15 dBu (0 dBu = .7746 vans) or as high as +20
dBu. The output of this level adjustment stage is fed into a 20
dB gain amplification stage 100 to raise the signal level to a
suitable operating level for a low pass filter 102. The
amplifier 100 may also be a Type 990 from The Hardy Company. The
preferred low pass filter is manufactured by the Apogee
Electronics Corp., of Santa Monica CA, and is known as a Type-
944G low pass filter. This filter removes any frequency
component of the input signal that has a frequency which is
higher than 22 KIiz, to prevent the analog-to-digital converter
from misconstruing or 'aliasing' the signal. That is, alaising
occurs if a signal is sampled at a frequency which is less than
twice its cycle, which result in a misreading of the samples as a
false signal of a relatively low frequency.
The output of the low pass .filter 102 is then fed into a
level boost buffer amplifier 104 to bring the peak information of
the signal up 14 dB to the maximum input of the analog-to-digital
converter, the amplifier also being preferably a Type 990 from
The Hardy Company.
The output of the level boost amplifier stage 104 is fed
into the analog-to-digital converter 106, which may be a device
manufactured by Analog Solutions Inc., of San Jose CA, and known
as a ZAD-2716 analog-to-digital converter. This particular type
of converter is used because it is able to over-sample the analog
input signal by at least two times the normal sampling rate of
44.1 KHZ. A stream of 2X sample clock pulses on wire 107 goes
into the timing sequencer 108, where it is sent over wire 110 to
the analog-to-digital converter. When the converter 106 finishes
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converting the signal, it informs the timing sequences by pulsing
the DONE line 112.
The data output from the analog-to-digital converter 106 is
a current sample of 16-bits of parallel data which is output onto
bus 114. The timing sequences 108 waits for adder 116 to add
this sample to the last sample stored at last latch circuit 118
which was latched after the last sample. After the adding is
completed, sequences 108 then latches the resulting 16-bit
addition into the output register 120 via bus 122. This addition
step effectively averages the current sample with the last
sample, and thus cuts out any vexy high frequency components of
the signal. The timing sequences 108 latches this current sample
into the last sample latch circuit 118 for addition to the next
following sample. Then, the timing sequences 108 informs the
storage control processor 68 (FIG. 3) that it is done or has
finished by pulsing the REQ line 62 (FIG. 3). After the storage
control processor has received the data, it pulses the ACK line
66 (FIG. 3).
Figure 8 is a detailed timing diagram showing a preferred
timing of the sequences 108 (FIG. 7) and showing the sample
control timing of the analog-to-digital converter 34 unit as
described above. This version of system timing averages each
pair of numbers into the sample data.
It is thought that this timing chart can be understood by
reading the information on it. In general, until the conversion
is complete, the time sequences 108 latches the last data 118 and
then an idle check is made to see if the data is still coming in
from the converter 34. Next, there is a delay which allows a
data word to be received, again followed by an idle check to
determine whether data is still coming in. The data is latched
into output register 120 and once more an idle check is made to
see if data is still coming in. Then, a DONE command is given
via wire 112 following which an idle check is made. If any of
these idle checks test positively to indicate that data is no
longer coming, in there is a general reset.
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Figure 9 shows an alternate detailed timing diagram for the
timing sequencer 108 which may be used for the sample control
timing of the analog-to-digital converter 34 unit. This version
averages the present sample with the last sample, and
continuously slides the samples down one sample period.
The principal differences between the timing of FIGS 8, 9 is
that the FIG. 9 timing delay extends directly to the step of the
output register 120 without the intermediate check over the last
data latch. In FIG. 9, the last data latch is checked after the
end of the output register check.
Figure l0 is a detailed timing diagram showing the timing
sequence for the host input/output control timing of the analog-
to-digital converter 34 unit. In greater detail, the sequencer
simply requests the input of data, measures a time period during
which a conversion is made and then requests the input of more
data. Idle checks are made after each step to see if data is
still coming in. A general reset is made whenever it is found
that there is no incoming data.
Figure 11 shows the overall block diagram of the duplication
machine. This machine receives the data which was stored on
video tape cassettes by the machine of FIGS 1-10 and converts
such stored data into information which is stored on audio tape
cassettes or the like and which may be duplicated once or
hundreds or thousands of times without having to re-read the
video cassette.
In greater detail, the operator first loads the library
master tape into a tape drive 150 (which may be the same as FIG.
5) in the duplication machine, and then initiates a load sequence
via the control panel and computer 152. The control computer
152 then attempts to read the tape in the tape drive 150. A
single master tape usually contains several duplicate copies of
the source material, so that if an error occurs while the machine
is reading the present section of the tape, the error will be
found by comparing the next readout with the data that was stored
during the last read out. Thus, errors in stored data are
.. 1340fi23
detected when the data which is read out from the tape is
compared with the data which is found when the tape is advanced
to read out the same data on the next available section of tape.
The data arrives via bus 155 in a parallel form and is
stored into long term electronic data storage memory 156, and is
sequentially stored in location after location until the end of
the present tape data segment. After all data has been read, the
tape in the video cassette can be rewound. The cassette is
ejected from the tape drive.
The control panel 152 now displays all current machine setup
parameters such as cue tone frequAncy, cue tone length, cut tone
placement, elapsed time between copies, total tape elapsed time,
and duplication speed. The cue tone is used to mark the end of
one copy and the beginning of the next copy, so that when the
pancakes are loaded into cassette shells, the end of one copy
and the beginning of the next copy can be determined. If any of
these parameters need to be changed, the operator enters the
correct value on panel 152.
The operator starts the machine by pressing a suitable start
button (not shown) on control panel 152. Displays on the control
panel show present tape time, total number of copied selections,
cue tone information, machine duplication speed ratio, and other
vital statistics. At the start of this sequence, the control
computer sets a start address which identifies both the data and
the total length of the data which is to be read out during the
duplication recording of the program material onto an audio tape
cassette.
Data is read out of the long term electronic data storage
memory 156, one data word after another, in a parallel data
format. This parallel data is. sent to digital-to-analog
converter 158 where it is converted into an analog signal.
There is one converter 158 for each channel or slave recording
device 160. This read out data flows at a speed that is
proportional to the duplication speed, which is usually
substantially faster than real time. The converted analog
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signals go to the slave recording devices where they are put onto
tape, film, disc, or whatever recording media is being used.
This process continues until the end of the source material
is reached, at which time a cue tone is generated. When the cue
tone is finished, a control processor in panel 152 resets to the
start address of the source material which is reproduced again.
This procedure continues until the operator stops the machine, or
until all slaves 160 are out of tape.
To help increase production, the operation of the slave
transports can be staggered so that all do not run out of tape at
the same time. For example, slave transport #1 will be making,
say, copy 5 while slave transport #2 is making copy 12. This
way, the operator can be placing a new reel of tape in the
transport of slave recorder #l~while all other slaves are
running. Then, a few minutes later, the operator can place a new
reel of tape,in the transport of slave #2. The machine aids the
operator by starting the transportation of a freshly loaded slave
at the correct time so that it is up to speed when the master
starts reading out its next round of source material.
A major advantage of the inventive system is that once the
master has been put into electronic storage, it may run
indefinitely at any speed, with no further wear on the library
master source. The library master tape is read only once during
a duplication run while the data stored in the electronic memory
is non-destructively read out many times. The master tape in the
video cassette is removed and placed on the shelf.
Figure 12 shows the details of the duplication machine's
long term data storage circuit. The tape drive (same as FIG. 5)
is started when the operator initiates a tape load command.
Then, via wire 165) the tape drive requests service from the
storage controller 166. The storage controller reads the data
from the video cassette in drive 150 (FIG. 11), which data
arrives via wires 155, either in parallel data form or as SCSI
data packets, depending on the interface used on the tape drive.
Tha data is sent along with an address into the memory array 170
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where it is stored at a selected location identified by such
address. After the electronic memory array 170 (which may be the
same as FIG. 4) has received the complete data that is read out
of the video cassette tape, a control computer in controller 166
determines the ending location of the master material. The data
coming in from the tape drive never stops coming until the end of
tape data has been reached. When the output of the data is
started to the slave transports, the data is read out of the
electronic memory array 170 through the storage controller 166
and bus 172 to the analog-to-digital converters in a parallel
data form. ,
Since the data is electronically stored at 170, the memory
storage may be read out either way, from beginning to end or from
end to beginning. Therefore, all audio channels on both the A
side and the B side of the audio tape may be read out
simultaneously via wires 172. The A side signals are read out
and recorded from beginning to end and the B side signals are
simultaneously read out and recorded from end to beginning.
Figure 13 shows, in greater detail, the data storage
controller 166 for the duplicating machine. When the operator
issues the tape read command, the control processor 174 sets the
storage base address in the input base address generator 176.
The input REQ line 177 is marked to indicate that data is
available on the data input lines 168. The data words are then
latched one by one in the input latch circuit 178. As each data
word is so latched, an address is generated by the input address
generator 176. This address is then sent along with the data and
a write command to the memory array 170. After the writing is
done, the address is incremented in generator 176. An
acknowledgement signal is returned on the ACK line 179 to tell
the tape drive that the next data word can be accepted. The next
set of data words is sent from the tape drive and is latched into
the input latch circuit 178. This sequence of data transfer
continues until the entire cycle of data has been read from the
video cassette and recorded in electronic memory array 170.
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When the operator starts the output duplication cycle, the
control processor 174 sets the base address into the output
address generator 180, at the beginning of the source material
data. The analog-to-digital converters 158 (FIG. 11) then use
the REQ line 182 to request data to be sent, word by word, from
the storage controller 166 (FIGS. 12, 13). As each of the data
words are requested) the address generator 180 sends an address
and a read command to the electronic memory array 170. The data
in memory 170 which is at the location selected by the address is
then latched into the output data latch circuit 184. The
processor 174 in storage controller 166 informs the analog-to-
digital converters 158 (FIG. 11) of the available data by pulsing
the ACK line 186. After an entire cycle of source material has
been written into the duplicate tape, the control processor 174
resets the base address generator 180 to the beginning address of
the source data. Another duplication cycle is performed. This
process continues until the operator issues a stop command.
The electronic memory array 170 (FIG. 13) is substantially
the same as the array shown in FIG. 4. However, the array shown
in FIG. 4 is usually large enough to store a single selection of
information that is being assembled and recorded on a video tape
cassette. Each selection may be added as an independent unit of
data that is recorded on the master tape as it becomes available.
The electronic memory array in memory 170 of FIG..13 is large
enough to store an entire album as it is read off the library
master tape. Thus, the electronic memory array storage 50 (FIG.
2) in the mastering machine may be in the order of 256-512 1M bit
chips, while the electronic memory array 170 (FIG. 13) in the
duplicating machine may have a memory containing in the order of
4,000-4,250 chips in order to store an entire album (about 45
minutes of recorded time).
The duplication machine has a control drive circuit which is
substantially the same as the drive shown in FIG. 5.
Figure 14 provides the details of one of the digital to
analog converters 158. The sample clock rate is set by clock
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pulses appearing on line 190, at a cyclic repetition rate which
is set by the desired converter output speed. For example, if a
sampling clock rate of 44.1 KHz is used, there is a 1:1
duplication ratio. A sampling clock rate of 88.2 KHz is equal to
a 2:1 duplication ratio, etc. Other clock rates lead to other
duplication ratios. As each sample clock pulse comes in on line
190, the control sequences 191 pulses the REQ line 182 to inform
the storage controller 166 (FIG. 13) that it needs more data.
When the data is present on the parallel digital inputs 188 (FIG..
14), the storage controller 166 pulses the ACK line 186 to inform
the control sequences 191 that the data is valid. The control
sequences 191 then latches the data into the input latch circuit
192. Once the data has stabilized in the input latch circuit
192, it proceeds into the digital-to-analog converter 194, as
parallel data.
When all of the data has arrived, the control sequences 191
pulsing a digital Go pin to tell the digital-to-analog converter
194 to convert the data into an analog form. The converter 194
then converts the digital data to an analog signal which
proceeds into the low pass filter 196 which is used to remove or
smooth out the "'stair-step° effect in the output which is created
by the digital-to-analog converter. If no low pass filter is
used, the analog output would have extra high frequency noise
caused by the stair-step effect that could potent;ally conflict
with the bias that is used to record the signal onto the slave
tape recorders.
The signal that emerges from the low pass filter 196 goes to
an adjustable output level control circuit 198 to adjust the
signal level so that different types of slave recording machines
can be accommodated. This level control circuit feeds an output
driver 200 that is used to drive the very high frequency signal
onto the cables 202 that go to the slave recording devices 160
(FIG. 11).
Figure 15 gives an example of a desired frequency response
for the low pass filter 196, based on the sample rate. If the
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sample rate is 1 Mhz, then the roll-off has to be completed
before one-half the sample rate, or in this case, 500 KFiz. As
can be seen from this example, a different low pass filter 196 is
selected for each different slave tape speed.
An alternative circuit (FIG. 16) for converting the digital
information into analog information provides a great improvement
since it eliminates a need for customized filtering. The method
of this digital-to-analog converting mathematically calculates
the appropriate analog samples in order to create a relatively
smooth curve so that low pass filtering is not required.
In greater detail, this digital-to-analog converter uses
mathematics to create multiple samples for each of the stored
samples. For example, if there are 44,100 samples which are
stored each second, there is a roll off of the high frequency
noise above 22.5 IGiz which avoids noise and distortion problems.
If mathematics is used to create four samples for each of the
available ones, the roll-off frequency increases to 88.1 IGiz.
This technique effectively removes the complex low-pass filter
from the digital-to-analog unit, and gives the freedom required
to run the recording output at any speed factor or duplication
ratio, without requiring any change in the output filter.
In essence, the higher the over-sampling frequency, the
better the circuit. In a system that uses only one standard
speed, it is not as important to use a high over-sample value.
For example, if a sample factor of four is used, the high
frequency is easy to filter off, because one constant speed
factor is used. Ideally, however, the sampling speed factor
should be adjustable so that any of many sampling speed factors
may be used. The invention provides such adjustability since the
clock speed of the circuit shown in FIG. 16 can be easily
changed by using a programmable divider 357 a and b for changing
the timing of the timing generator 348.
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The circuit of FIG. 16 operates this way. Data comes in
over a parallel data bus 366, and is latched into input latch
circuit 352. The subtractor 356 then determines the difference
between this current sample stored in latch circuit 352 and the
last previous sample that is stored in last latch circuit 354.
The difference between the two samples is then divided at 357b by
the over-sample rate factor 'N' (4, 8, 16, 32, etc.). The
accumulator 358 repeatedly adds the divided difference onto the
last sample in order to increment its value and thereby create N
small steps between any two successive samples. Each of these
added samples is then sent out of the accumulator 358 and on into
the digital-to-analog converter 360, one sample being added for
each of the over sample factors. The digital converter 360 then
converts the sample into an.analog signal that goes into a very
slightly high frequency roll off filter 362 to prevent an RF
pickup. This new analog signal is then run through an output
buffer 364 to drive the slave recording devices via analog output
370.
The improvement can be seen in Figure 17, which shows a
comparison of an ideal analog signal (solid line A), a standard
non-over sampled signal (stepped solid line B), and an over-
sampled signal with a factor of 16 (dotted line C). The ideal
signal (A) is a very smooth curve which is representative of the
original curve. The standard non-over-sampled, stair-step signal
(B) had very hard/sharp edges which are basically high frequency
components that need to be removed in order to make the signal
look more like the curve (A). The sixteen over-sampled signals
(C) in each sample period (the horizontal flat lines in curve B)
can be seen as a dramatic improvement over the non-over-sampled
signal (B). Basically, the over-sampled signal (C) is comprised
of four times sixteen very small steps as opposed to the one
original sample signal (B) which has four very large steps (in
the illustrated curve of FIG. 17)
The curve (C) limits the high frequency component of the
signal and removes the need for a steep roll-off filter.
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FIG. 18 shows the timing required for an over-sample
factor of sixteen. This sense timing in a slightly altered
form may be used for any other over-sample factor.
Those who are skilled in the art will readily
perceive how to modify the invention. Therefore, the appended
claims are to be construed to cover all equivalent structures
which fall within the true scope and spirit of the invention.
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