Voice actuated recording device having recovery of initial speech data after pause intervals

Informational data is efficiently recorded on a recording medium in response to an input signal containing information and pauses of different intervals. Information following each pause is captured for recording and space occupied on the recording medium for recording of the pauses is minimized. A stream of input data corresponding to the input signal is supplied by operation of a controller selectively to a first buffer and a second buffer arrangement. The input signal is also coupled to a record signal generating circuit that produces a record signal in response to an input signal having information of a certain duration, and produces a no-record signal in response to a pause in the input signal of a determined interval. The controller operates to store the supplied data at selected addresses from an initial address to a last address of the first buffer before a record signal is produced, and to recirculate data storage from the initial address to the last address after data is stored at the last address and the record signal generating circuit continues to output a no-record signal. When a record signal is produced, data from the first buffer is read out for recording prior to reading out of data from the second buffer. The controller also deletes from the buffered data, before recording, data corresponding to a pause in the input signal for the determined interval needed for the record signal generating circuit to switch from a record to a no-record signal output.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to voice actuated recording 
devices, and more particularly to a voice operated (VOX) recording device 
in which speech data that might be lost from recording due to time delays 
in the VOX circuitry and other recording components of the device, is 
recovered and stored for recording in proper sequence with speech sounds 
which follow after the VOX circuitry signals the device to record. 
2. Description of the Known Art 
Recording devices are used to capture various data including speech in 
analog or digital form. The data is permanently recorded on media such as 
magnetic tape. Several different methods of recording are possible. First, 
the recording device can be left in an ON state over a relatively long 
time during which an event to be recorded may occur. Second, if the 
operator of the device knows that an event to be recorded is about to 
happen, for example, someone giving dictation knows that he or she is 
about to speak, the person can manually start the recording device before 
speaking by operating a record button and setting the device in an ON 
state early enough to capture all of the speech. Third, some kind of 
automatic start and stop feature responsive to the presence of speech, 
e.g., VOX control, can be embodied in the recording device. 
The first mentioned recording method has the obvious disadvantage that the 
recording device might be set in an operating state over a time 
substantially longer than that during which any speech is present. Once 
incident on the device, however, the speech will be captured in its 
entirety on the recording medium. This method therefore gives rise to a 
great deal of wasted media if the speech events are only occasional, with 
less waste as the speech becomes more continuous. 
In the second method--manual operation of the recording device--the 
operator must be sure to set the device in an ON state before commencing 
speech. If done properly, the recording media will be used much more 
efficiently in terms of blank or wasted space. 
In the third method of recording mentioned above, a sensor arrangement 
known as voice operated switch or a VOX is used to detect the speech and, 
once detected, sets the recording device in an ON state by outputting a 
VOX speech detection signal. The media is used efficiently in that pauses 
greater than the cut-off time for the speech detection signal are not 
recorded. Upon playback, the listener need not wait through a number of 
long pause intervals. 
Accordingly, the most efficient use of recording media for dictation and 
other speech applications entails automated ON-OFF control of the 
recording device, wherein the device records only upon the presence of 
speech. VOX circuitry can be used to accomplish such automation. There 
are, however, problems associated with the conventional VOX actuated 
recording devices. Specifically, in a typical speech recording device such 
as a tape recorder, a length of magnetic tape is driven by a mechanical 
motor. The motor drives the tape up to an operating speed so that proper 
recording can take place. Using the VOX speech detection signal as a means 
for starting the motor therefore has the disadvantage that speech present 
before the speech detection signal is produced will not be recorded at the 
beginning of the recorded data. Yet, this initial speech includes the 
beginning sounds of words and usually contains critical phonemes. If this 
speech is lost from recording, it may be impossible for the listener 
during playback to comprehend the initial part of the recording. In other 
words, VOX circuitry must respond to the presence of speech in order to 
actuate the drive motor, but since the VOX has an inherent finite time 
delay, and since the drive motor does not come up to speed 
instantaneously, a time lag between the beginning of speech and the 
recording of the speech is created. The portion of the speech omitted from 
recording corresponds to this time lag. 
Further, when speech is completed or a relatively long pause is taken 
between words and sentences, the VOX ceases to produce an output signal 
and the drive motor is stopped. Again, there is a finite response time for 
the VOX to cut off its output signal once speech is no longer present. 
That portion of the record media which continues to be driven over this 
response time is wasted since no speech is being recorded. Finally, VOX 
circuitry may switch ON and OFF during a sentence or word, instead of 
between sentences and pauses. By causing the tape drive to be turned OFF 
and back ON quickly, some of the speech may be lost from recording. 
U.S. Pat. No. 4,893,197 issued Jan. 9, 1990, discloses sound recording 
apparatus in which pauses during speech to be recorded are compressed into 
the form of pause length data bytes, so as to minimize waste of recording 
media. The patented apparatus does not use a VOX arrangement for 
controlling the speech recording process, but instead remains in an "on" 
state all the time. An input analog audio signal is converted to digital 
form and loaded at successive addresses in a temporary store. Pauses of 
more than a certain length are detected and their lengths are encoded. 
Data corresponding to the encoded pause length is then loaded in the 
temporary store at an appropriate address, and additional addresses of the 
temporary store are not written until an end of each pause is detected. 
The data structure of the recording apparatus of the '197 patent is 
therefore comprised of simple speech data bytes and specially encoded 
pause length data bytes. It will be appreciated that such a data structure 
requires substantial central processing unit (CPU) resources to create 
during record, and to decode, upon a playback operation. 
SUMMARY OF THE INVENTION 
An object of the invention is to overcome the above and other shortcomings 
of voice actuated recording devices. 
Another object of the invention is to provide a voice actuated recording 
device in which initial speech signals that contain distinguishing 
phonemes and other important information will not be lost upon recording 
and subsequent playback. 
Yet another object of the invention is to provide a speech recording device 
in which a conventional VOX may be used to detect the presence of speech 
and in which initial speech signals that are present before the VOX 
signals a speech condition, are captured and recorded. 
According to the invention, a data recording system for efficiently 
recording signals containing information and pauses of different 
intervals, wherein information following each pause is captured for 
recording and space occupied on a recording medium for recording of the 
pauses is minimized, comprises input means for supplying an input signal 
containing information to be processed for recording on the recording 
medium, processor means coupled to the input means for supplying a stream 
of input data corresponding to the input signal, and storage means 
including first buffer means and second buffer means coupled to the 
processor means for storing data supplied by the processor means. 
Control means coupled to the processor means and the storage means operates 
to control a sequence of operations of the recording system and to enable 
the storing of data in and out of selected addresses of the first and the 
second buffer means. The system also includes record signal generating 
means having an input coupled to the input means and an output, for 
producing a record signal in response to an input signal having 
information of a certain duration and for producing a no-record signal in 
response to a pause in the input signal of a determined interval, said 
output being coupled to an input of the control means, and the first 
buffer means has a storage capacity corresponding to said information of a 
certain duration. 
The control means includes first means for storing data supplied from the 
processor means at selected addresses from an initial to a last address of 
the first buffer means before a record signal is produced by the record 
signal generating means, including means for recirculating data storage 
from the initial address to the last address after data is stored at the 
last address and the record signal generating means continues to output a 
no-record signal; second means for reading out data stored in the first 
buffer means after a record signal is produced, third means for storing 
data supplied from the processor means at selected addresses of the second 
buffer means after a record signal is produced, fourth means for reading 
out data stored in the second buffer means following the data read out 
from the first buffer means, fifth means for returning data storage to the 
control of the first means when the recording signal from the record 
signal generating means changes from a record to a no-record signal, sixth 
means for measuring lengths of pauses in buffered data in the storage 
means and for encoding the pause lengths at corresponding positions in the 
data for recording on the recording medium, and seventh means for deleting 
from the buffered data, before recording, data corresponding to a pause in 
the input signal for said determined interval when the signal from the 
record signal generating means changes to a no-record signal. 
According to another aspect of the invention, a method of efficiently 
recording signals containing information and pauses of different 
intervals, whereby information following each pause is captured for 
recording and space occupied on a recording medium to record the pauses is 
minimized, comprises the steps of supplying an input signal containing 
information to be processed for recording on a recording medium, 
processing the input signal to produce a stream of input data 
corresponding to the input signal, coupling the input signal to record 
signal generating means thereby producing a record signal in response to 
an input signal containing information of a certain duration and producing 
a no-record signal in response to a pause in the input signal of a 
determined interval, and providing storage means including first buffer 
means with a data storage capacity corresponding to the information of a 
certain duration, and second buffer means. 
The method also includes first controlling the first buffer means to store 
the stream of input data before a record signal is produced and to read 
out the data stored in the first buffer means after a record signal is 
produced, second controlling the second buffer means to store the stream 
of input data after a record signal is produced and to read out data 
stored in the second buffer means following the data read out from the 
first buffer means, returning to the first controlling step when the 
record signal from the record signal generating means changes to a 
no-record signal, measuring lengths of pauses in buffered data in the 
storage means and encoding the pause lengths at corresponding positions in 
the data for recording on the recording medium, and deleting from the 
buffered data, before recording, data corresponding to a pause in the 
input signal for said determined interval when the signal from the record 
signal generating means changes to a no-record signal. 
According to another aspect of the invention, a recording system for 
efficiently recording signals containing speech information including 
pauses of different intervals, comprises input means for supplying a 
speech signal containing speech information and pauses of different 
intervals, with processor means for supplying a stream of speech data 
corresponding to the speech information and pause data corresponding to 
the pauses of different intervals. Storage means coupled to the input 
means stores data supplied by the processor means, and control means 
coupled to the input means and to the storage means includes address and 
read/write enable means for controlling a sequence of operations of the 
recording system, and for enabling storing and reading of data in and out 
of selected addresses of the storage means. Record means coupled to the 
control means and to the storage means transfers speech data read out of 
the storage means for recording on a recording medium, wherein the control 
means comprises means for measuring lengths and positions of the pauses in 
the supplied speech information, including pause indexing means responsive 
to the pause data for producing flags corresponding to a position and a 
length of each of the pauses in association with a file of speech data 
recorded on the recording medium. 
According to another aspect of the invention, a method of efficiently 
recording signals containing speech information including pauses of 
different intervals, comprises the steps of supplying a speech signal 
containing speech information and pauses of different intervals, 
processing the speech signal to produce a stream of speech data 
corresponding to the speech information and pause data corresponding to 
the pauses of different intervals, providing storage means, controlling 
the storage means to store and to read data in and out of selected 
addresses of the storage means, transferring speech data read out of the 
storage means for recording on a recording medium, measuring lengths and 
positions of pauses in the supplied speech signal according to the pause 
data, and producing flags corresponding to a position and a length of each 
of the pauses in association with a file of speech data recorded on the 
recording medium. 
For a better understanding of the present invention, together with other 
and further objects, reference is made to the following description taken 
in conjunction with the accompanying drawing, and the scope of the 
invention will be pointed out in the appended claims.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a schematic block diagram of voice actuated speech recording 
device 10 according to the invention. 
Speech to be recorded during, for example, a period of dictation is 
incident upon a microphone element 12 and transformed into electrical 
speech signals f(t) corresponding to the spoken words. The signal f(t) is 
simultaneously monitored by a speech detector circuit 14 which can be a 
conventional VOX circuit, and by an optional speech processor 16 for 
performing a desired operation on the signals f(t) prior to their being 
recorded on a recording medium. For example, speech processor 16 may 
convert the analog signals f(t) into digital form as represented at 17 in 
FIG. 1, and perform digital signal processing such as filtering and/or 
removing noise from the speech signal f(t). 
The sequence of operation of the various components of the recording device 
10 are controlled by controller 18 which may include a central processing 
unit (CPU), a read-only-memory (ROM) in which an operating program for the 
device 10 is permanently stored, one or more random access memories 
(RAMs), and various input-output (I/0) devices such as may be necessary to 
interface the controller 18 with other components of the recording device 
10. 
In the illustrated embodiment, speech data bytes output at 17 from the 
speech processor 16 are loaded into storage means 20 under the control of 
a buffer address and read/write stage 19 associated with controller 18. 
Storage means 20 is comprised of a ring buffer 22, and two larger capacity 
buffers 24, 26 of equal size. Speech data stored in the three buffers 22, 
24, 26 is read out at a controlled timing via the buffer address and 
read/write stage 19 into a gate network 28 the output of which comprises 
speech data to be recorded on the recording medium. The recording medium 
may comprise, for example, a magnetic disk storage arrangement in a 
personal computer (PC). 
The speech detector or VOX circuit 14 produces an output speech detection 
signal 30 when the input speech signal f(t) exceeds a preset level. As 
mentioned, VOX circuit 14 has a certain inherent response time prior to 
signaling of a speech condition. Also, after relatively long pauses such 
as between sentences and paragraphs, the speech detection signal 30 is no 
longer output by VOX circuit 14. 
Speech detection signal 30 is input to an integrate circuit 32 the output 
of which is supplied to a threshold detector circuit 34. Threshold 
detector 34 generates a record signal 36 which is input to the controller 
18 once the integrated speech detection signal exceeds a certain 
threshold. As discussed below, all speech incident on the microphone 
element 12 prior to generation of the record signal 36 is recovered and 
stored in the ring buffer 22 of the storage means 20. Thus, this initial 
speech data is captured by the device 10 for recording on the recording 
medium. 
The storage means 20, integrate circuit 32 and threshold detector 34 
together form what may be referred to as a "recording switch modifier" 
(RSM). The RSM is two-part. One part, the integrate circuit 32 and 
threshold detector circuit 34, takes the speech detection signal 30 output 
from an ordinary speech detector or VOX circuit 14 and processes the 
signal. The other part, i.e., storage means 20 employs a buffering 
arrangement to store speech data prior to permanent recording. The RSM 
therefore operates in parallel with respect to a stream of speech data. 
The output record signal 36 serves to control the gate network 28 or 
equivalent switch via controller 18 for enabling a permanent recording of 
the speech data. The buffering arrangement of the storage means 20, and 
any time delays inherent in the speech processor 16, create a time delay 
between the incidence of speech on the microphone element 12 and its 
permanent recording. Speech data is continuously recorded into the ring 
buffer 22 of storage means 20. As more data is input, it is loaded into 
the ring buffer 22 until full. If the buffer 22 becomes full before the 
RSM generates the record signal 36, the oldest data is discarded as new 
data is written in. The operation is therefore of a first-in first-out 
kind similar to a queue in a computer. Once the RSM produces the record 
signal 36, speech data is enabled to pass through the gate network 28 to 
be properly recorded on the recording medium. Speech data which would 
otherwise be lost prior to signaling of the VOX circuit 14, is therefore 
captured by ring buffer 22. 
In a system where digitized speech is generated by speech processor 16 or 
from some other source at a sample rate of 8,000 samples/second (telephone 
quality), ring buffer 22 may have, for example, a capacity of 2000 bytes. 
This storage capacity corresponds to a maximum time delay of 0.250 
seconds. A range of possible time delays has been found to be from about 
0.1875 to about 0.320 seconds for high telephone quality. Smaller time 
delays will definitely clip data, while longer delays will waste some 
media. Other constants depend on the application. 
In summary, operation of the RSM portion of the recording device 10 is as 
follows. Taking the output of a VOX circuit 14, the speech detection 
signal 30 is processed so as to produce the record signal 36 after a 
predetermined time delay. This is accomplished by integrating the speech 
detection signal 30 over time, and then passing the integrated signal to 
the threshold detector 34. As is known, the VOX circuit 14 provides a 
logical true or false condition (logic 1=no speech, and logic 0=speech) as 
speech signals are input. Integrating the logical speech detection signal 
30 over time during a "no-speech" condition results in an integrated 
logical 1 signal. Upon incidence of speech, the VOX circuit 14 toggles 
back and forth between "speech" and "no-speech" (logical 0 and 1). 
Integrating this signal over time during the course of speech results in a 
time averaged signal value between the "speech" and "no-speech" signal 
values. The integrated signal is supplied to the threshold detector 
circuit 34 which determines whether or not the record signal 36 should be 
generated. 
FIG. 2 is a schematic diagram of the speech detector circuit 14, integrate 
circuit 32 and threshold detector circuit 34. 
The speech detector or VOX circuit 14 may be constructed from a 
conventional operational amplifier such as an IC type 1458 (U1) operating 
in a non-linear mode. The output of U1 (OUT A) is therefore either+5 
volts, or -5 volts. When no speech signal f(t) is present speech detection 
signal 30 is at+5 volts as set by the equation V 
(detect)=10,000.times.(VTH1-V speech). A threshold voltage (VTH1) is set 
by resistors R2 and R3. As the incoming speech signal f(t) reaches the 
threshold voltage, the output of U1 shifts from+5 to-5 volts. When the 
signal falls below the threshold, the output shifts back from-5 to+5 
volts. 
The output speech detection signal 30 is supplied to the integrate circuit 
32 comprised of resistor R1, capacitor C1 and diode D1. Capacitor C1 
charges through resistor R1 by the positive voltage detection signal 30, 
i.e., a "no speech" signal of+15 volts. If the signal 30 falls below VTH2, 
diode D1 opens and capacitor C1 discharges directly into U1. The effect of 
the charging and the discharging of capacitor C1 is to average the speech 
detection signal 30 over time so that it will approach 0 volts while a 
person is speaking, and+5 volts during a no-speech condition. Threshold 
detector circuit 34 may comprise a conventional IC type 555 timing chip 
(U2) used to monitor the voltage VTH2. As is known from the conventional 
operating parameters for the type 555 IC, as long as its threshold pin 
input VTH2 is above the threshold voltage 2/3.times.5 volts, the output 
record signal 36 is low. When the voltage VTH2 falls below this threshold 
voltage, the output record signal 36 switches high. 
Thus, according to the combined circuitry of FIG. 2, when speech detector 
or VOX 14 signals a no-speech condition, the detection signal 30 is high 
so as to charge capacitor C1 beyond the threshold voltage, and U2 is set 
low to indicate a "no-record" state. When a signal is present, capacitor 
C1 averages the output of the VOX (U1) which, upon lowering to the 
threshold voltage, sets U2 to a "record" state. When the signal goes from 
"speech" to "no-speech", the capacitor C1 charges slowly (set by R1 and 
C1) to the threshold voltage which allows a small period of time before 
the output of U2 goes low again. This period of time is that which keeps 
the circuit from changing states during relatively small pauses between 
spoken words and phrases. 
The implementation of buffering in the storage means 20 in FIG. 1 is now 
discussed in further detail, with reference to the flow chart of FIG. 3. 
When the speech signals f(t) are converted into digital form at 16, a data 
stream representing digitally processed speech data bytes is generated. As 
the bytes become available, they are written into the storage means 20 
which comprises the ring buffer 22, and larger buffers 24, 26. Ring buffer 
22 is used only to buffer the data prior to the signaling of a record 
state by the threshold detector 34. See steps S1 to S4. The buffers 24, 26 
are of larger capacity and are used to capture data before being written 
to a recording medium such as, e.g., a magnetic disk in a PC. The data is 
stored in the three buffers in a rotating fashion. As each data byte is 
read into the storage means 20, a write pointer is incremented to a next 
address location. The pointer is used to instruct the CPU of the 
controller 18 as to where the next speech data byte is to be written, and 
is 
functionally equivalent to "pushing" data along a queue. 
If the pointer indicates a last available address of the ring buffer 22 
before a record signal 36 is loaded, the pointer is returned to the 
beginning or first address of the ring buffer 22. (Step S3). Once a record 
signal 36 is produced (S4), the write pointer is moved to a first address 
for the buffer 24, and speech data is then written into buffer 24 until 
full. (Step S5). Once the latter buffer is filled, the pointer indicates 
the beginning or first address of buffer 26 into which speech data 
continues to be stored. The gate network 28 is then opened. (Step S6). 
Prior to writing of the contents of buffer 24 onto the recording medium, 
however, the contents of the ring buffer 22 which contains speech data 
prior to signaling of a "record" condition by threshold detector circuit 
34, must be included. Accordingly, prior to reading out of the contents of 
buffer 24 to the recording medium, the contents of ring buffer 22 are 
unloaded in a first-in first-out manner through the gate network 28 (Step 
S7), followed by the contents of buffer 24. (Step S8). 
Once buffer 26 is filled with speech data bytes, the pointer is then moved 
back to indicate the first address of buffer 24 for writing of new speech 
data while buffer 26 is unloaded through gate network 28. (Step S9). Input 
speech data is stored in buffer 24 until full, and then switched to buffer 
26 while the contents of buffer 24 are read out to be recorded through the 
gate network 28. 
When the threshold detector circuit 34 signals a "no-record" condition 
(S10), the remaining contents of the buffers 24, 26 are read out and the 
pointer is then set to indicate the first address of the ring buffer 22. 
The process then returns to step S1. 
The above described RSM portion of the recording device 10 thus avoids 
wasting of recording media when a flow of speech ends. If the RSM signals 
"no-record" via threshold detector circuit 34, a small amount of buffered 
data corresponding to the "off" time delay of the RSM can be deleted. If a 
co-processor or very fast processor is included in the overall system, it 
could monitor the buffered speech data stream and determine whether or not 
the data represents a pause or a true end of speech. If the processor is 
fast enough, real-time pauses that are not dropped by operation of the RSM 
can be flagged and removed. Even apart from such real-time processing of 
pauses, the RSM will detect an end of speech via the threshold detector 
circuit 34, and relatively little recording media will be wasted. The RSM 
nonetheless allows for a post hoc analysis of pauses. 
In order to recreate an original message as spoken, pauses can be detected 
and reinserted upon playback. The pause lengths and positions may be 
measured during recording, and encoded on the recording medium. When 
playing back a recording, the speech is played until a previously marked 
pause is encountered, and "blanks" are played for the measured time 
duration of the pause. Such capability is important for purposes of 
editing and purposeful exaggeration of pauses during speech to parse 
speech. 
By marking a recorded file of speech data for pauses, editing can be 
facilitated. If one requires that a pause be deleted or lengthened, such 
can be easily accommodated. Such pause marks also provide convenient 
locations for tabbing through a file for insertions and deletions. If a 
person while dictating speech follows a simple set of rules in forming 
pronounced pauses, it will not be necessary, for example, to say 
"paragraph" or "stop". 
The recording device 10, as disclosed herein, uses a combination of analog 
and digital technology. The VOX 14 monitors the analog speech signal f(t) 
and produces an analog speech detection signal 30. The integrate circuit 
32 monitors the VOX output and also produces an analog integrated speech 
detection signal. The threshold detector circuit 34 senses the integrated 
detection signal 30 and produces a logical record/no-record output signal. 
The buffers 22, 24, 26 of the storage means 20 are shown in a digital 
form. While the presently disclosed arrangement is an analog/digital mix, 
it will be appreciated that it can be realized in strictly analog or in 
strictly digital form. 
For example, an analog implementation allows the VOX, integrate and 
threshold detector circuits to remain as disclosed. Instead of processing 
the speech signals f(t) into a data byte stream and using digital memory 
devices, the storage means 20 may be in the form of an analog delay line. 
The recording medium can be in the form of magnetic tape as with tape 
recorders, or optical media as in laser recordings. 
An all digital implementation would require the VOX, integrate and 
threshold detector circuits of FIG. 2 to be implemented via digital 
technology. The VOX circuit 14 would monitor digitized speech rather than 
analog and can be implemented via an algorithm which operates on the 
speech data, wherein a VOX output would be computed by a processor. 
Similarly, the integrate and threshold detector circuits 32, 34 could be 
implemented by a processor programmed to carry out the same functions as 
the analog circuits disclosed. 
To play back messages recorded via the present recording device 10 onto a 
recording medium, one need keep track only of the number of bytes written 
during recording or, if the RSM signals a "no record" state, the number of 
bytes read in but not saved. During playback, the data saved may be played 
back until the number of bytes associated with that packet is played. 
Then, a number of blanks associated with the number of bytes counted 
during the pause period may be inserted. If selected, this operation is 
repeated until the original file is played back as it was recorded. 
Alternatively, during playback, pauses can be exaggerated for purposes of, 
for example, language instruction. 
Compression of speech data pays off in a direct savings of recording media. 
In digital systems where media is expensive, any savings of storage 
represents a direct savings in cost. Also, by eliminating pauses, a user 
is spared from listening to the pauses on playback should such pauses not 
provide any useful information, resulting in a reduced time needed to 
review the recording. Further, rather than writing on magnetic disk, 
compressed speech can be written to an audio tape recorder. Audio tape is 
useful where magnetic disk space is at a premium. By writing to audio 
tape, the user gains the advantage of being able to listen to the 
recording away from a PC. 
Speech data ordinarily uses up a considerable amount of record media space. 
If digitized, however, speech data may be compressed prior to recording 
through an algorithm known as Adaptive Pulse Code Modulation (ADPCM), 
which is implemented via hardware. The algorithm takes 10 bit serial data 
and converts it to either 3 or 4 bits (software selectable). After two 
such samples have been taken, a single byte of data is assembled. As 
discussed above, the speech may be further compressed by removing pauses 
between sentences in order to minimize the amount of record media space 
used. By keeping track of the length of the pauses and their position in 
the record file, the stored message can be reproduced as actually spoken 
by inserting the pauses back into the message at playback. 
Compression of the recorded speech data can be implemented in two 
ways--software and hardware. A software approach entails monitoring the 
input speech data stream at 17, and carrying out a pattern recognition of 
the data. By removing bytes that represent silence and keeping track of 
their number and position, an accurate reproduction can be made. This type 
of compression can be done both at run-time, or as a post process. 
The presently disclosed embodiment incorporates a hardware approach to real 
time speech compression by use of a recording switch modifier (RSM), as 
well as that software necessary to read stored speech data out of the 
storage means 20 including the ring buffer 22 and large buffers 24, 26. At 
least part of the RSM may be in the form of an "add-on" board for a PC, 
and other parts such as the buffers 22, 24, 26 and controller 18 may 
reside in the PC itself. 
It will be appreciated that the recording device 10 as disclosed herein 
provides the following features and advantages in the recording of speech: 
1. The use of a recording switch modifier (RSM) which processes the output 
of a conventional speech detector or VOX circuit to control the start and 
stop of speech data storage, as well as to keep unwanted noise from being 
recorded. 
2. Speech is compressed prior to permanent recording by removal of pauses 
exceeding a certain time duration, e.g., pauses between sentences. 
3. The use of storage means including a ring buffer to recover initial 
speech bursts or data that are present just prior to the signaling of a 
"record" state. 
4. A fully restored playback including original pauses may be obtained. 
Pauses may, however, be deleted or edited. The present device 10 allows 
for the enhancement of speech parsing. It improves dictation control by 
enabling a "backing up" to previous flags rather than over a fixed 
interval for inserting new dictation at the flag markers, and instead of 
having to record one larger unit of speech. 
5. Transcription of speech is facilitated by enabling the forward or 
backward movement to flag pauses. 
The RSM portion of the device 10 may be used to create a real-time 
recording in which speech data is compressed beyond that normally obtained 
with adaptive pulse code modulation algorithms. Data generated by the RSM 
can be interpreted in terms of pauses and can be used to compress data 
stored on the recording medium. Such compression may be large relative to 
ADPCM if the user's speech has a lot of pauses as is common when people 
dictate and/or record messages to some machine. In any event, the 
compression obtainable relative to ADPCM remains significant. 
Although the present recording device and technique are described in 
connection with VOX circuitry that outputs a speech detection signal, it 
will be appreciated that the invention can be applied to operate with any 
VOX type circuitry that produces a detection signal a finite time after 
any kind of recordable information signals are present at its input, e.g., 
music, video, seismographic, and the like. 
Further, while the disclosed embodiment incorporates digital circuit 
technology, it will be obvious that the present invention can be 
implemented in a purely analog fashion with, for example, delay lines and 
other suitable analog circuit technology. 
While the foregoing description represents a preferred embodiment of the 
invention, it will be obvious to those skilled in the art that various 
changes and modifications may be made, without departing from the true 
spirit and scope of the invention as defined by the following claims.