Information
-
Patent Grant
-
6658113
-
Patent Number
6,658,113
-
Date Filed
Tuesday, November 18, 199726 years ago
-
Date Issued
Tuesday, December 2, 200320 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Barrón; Gilberto
- Meislahn; Douglas
Agents
- McKee, Voorhees & Sease, P.L.C.
-
CPC
-
US Classifications
Field of Search
-
International Classifications
-
-
Disclaimer
Terminal disclaimer
Abstract
An apparatus and method for concealing data bursts in an analog scrambler using parts of the audio of a signal in substitution for the data bursts. What otherwise would be periodic data bursts appearing at the audio output are replaced with selected portions from audio portions of the multiplexed signal. Preferably the replaced audio samples come from immediately past and immediately future portions of the audio of the signal. The data bursts are therefore effectively concealed from the audio output which improves on the degradation of audio otherwise caused by the data bursts that are mixed in periodically with the audio portions of the signal.
Description
BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates to audio communication transmissions, and in particular, to such transmissions wherein data bursts are contained within the transmissions, and more particularly, to an apparatus and method to improve on the audio quality of such transmissions.
B. Problems in the Art
In co-pending, co-owned U.S. Ser. No. 08/689,397, filed Aug. 7, 1996, the concerns about improving audio quality of voice communications that include bursts of digital data (e.g. synchronization data) are set out and a proposed solution is disclosed. The bursts of audio are concealed by replacing the data bursts with, for example, a piece of immediately preceding audio. Essentially, a small part of the audio is replayed during the period a data burst would otherwise exist in the audio signal.
Thus, instead of the pops, snaps, and crackles that would be heard if the data bursts were not removed and were played through with the audio, and which at best are annoying and at worst degrade the audio to a point where critical audio is lost, a more natural or smoother audio is achieved.
However, there is still room for improvement in the audio output. The insertion of a section of audio in place of the data bursts puts audio (e.g. voice) in those locations, but the audio can at times have a stuttering effect because of this play back. Even though the length of a data burst is relatively short, it can be long enough to cover critical letter or syllabic information. Thus the repetition or play back of a preceding segment of voice, for example, can create a stuttering sound that is distracting or which degrades the quality of the audio noticeably. It is therefore the principal object of the present invention to further improve the audio output over that disclosed in U.S. Ser. No. 08/689,397 and the state of the art.
Furthermore it is the object of the present invention to provide an apparatus and method for concealing data bursts in an analog scrambler:
A. which conceals the data bursts by repeating audio taken from audio portions immediately prior to and immediately after each corresponding data burst of the transmission;
B. which conceals the data bursts in a manner which reduces distracting. audio effects;
C. which improves the sound quality of the audio to a listener;
D. which is adjustable for various sizes and types of data bursts;
F. which is implementable in several fashions, including with a digital signal processor; and
G. which is economical, efficient and durable in use.
These and other objects, features, and advantages of the present invention will become more apparent with reference to the accompanying specification and claims.
SUMMARY OF THE INVENTION
The invention includes a method of concealing data bursts in a transmitted time multiplexed signal, comprising periods of scrambled audio and periods of data bursts, by replacing at an audio output the data bursts with audio taken from the audio portions of the transmitted time multiplexed signal immediately prior to and immediately after each data burst. In one aspect of the invention, the replacement of the data bursts is accomplished by storing immediate past and immediate future audio samples from the signal and playing back those audio samples during receipt of a data burst. The replay of sampled audio is correlated to the length of a data burst.
The apparatus according to the present invention utilizes storage buffers that contain audio samples of immediate past and immediate future audio portions of the signal relative to each data burst, switching devices, and a control device to allow the audio portions of the signal to pass through the switching devices to an audio output, but changing states to pass stored audio samples to the audio output at those times when a data burst otherwise would be present at the audio output. The data bursts in the signal are therefore effectively concealed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic representation of an embodiment according to the present invention.
FIG. 2
is a diagrammatic representation of a storage buffer such as could be used with the embodiment of FIG.
1
.
FIG. 3
is a diagrammatic representation of signals at various points in the operation of the embodiment of FIG.
1
.
FIGS. 4 and 5
are examples of several weighting functions that can be used to smooth out the audio.
FIG. 6
is a schematic diagram of a software simulation of an embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
To better understand the invention, one embodiment thereof will now be described in detail. Frequent reference will be taken to the drawings. Reference numerals are used to indicate certain parts and locations in the drawings. The same reference numerals will be used to indicate the same parts and locations throughout the drawings in this description, unless otherwise indicated.
U.S. Ser. No. 08/689,397 can be consulted and its disclosure is incorporated by reference herein for background regarding the invention and this preferred embodiment.
FIG. 1
illustrates schematically an apparatus according to the present invention. In this embodiment, an audio input
12
receives a signal of the type diagrammatically depicted at reference numeral
50
in FIG.
3
. In this embodiment, signal
50
is a time-division multiplexed (TDM) signal consisting of audio portions (see reference numerals
62
in
FIG. 3
) with periodically interspersed data bursts (reference numeral
64
in FIG.
3
). Portions
62
are time varying analog waves representative of audio or speech. Portion
64
represents an analog carrier wave with modulated digital information contained therein.
As can be seen in
FIG. 1
, TDM signal
50
enters audio input
12
and passes to three locations. First to a first input
14
of a first switch device
16
. Second to the input of what will be called first storage buffer
18
. Third, to the input of what will be called second storage buffer
19
. It is to be understood that first buffer
18
stores signal
50
in a fashion whereby signal
50
is delayed by the equivalent length of time equal to N/2 samples. The quantity N will be defined later. Buffer
19
delays original signal
50
by N samples. Therefore, at any given time, the system has the ability to select from signal
50
, or signal
50
delayed by N/2 samples, or signal
50
delayed by N samples. The data bursts
64
are replaced with cut and pasted portions of non-data burst audio by switching between the three signals, again identical in content, but shifted in time relative to one another.
The output of storage buffer
18
appears at a first input
23
of a second switch device
17
. The output of storage buffer
19
appears at second input
15
to switch
16
. The output
22
of switch
16
is connected to the second input
21
to second switch
17
.
The output
22
of second switch
17
is directed to an audio processing circuit which converts the analog audio waveform in a manner that can then be output to a acoustic speaker.
FIG. 1
also shows that a first latch
24
has an output connected to what will be called time-delay device
26
, which has an output
28
which is connected to and controls the state of first switch
16
. Latch
24
is controlled by mid line
30
and stop line
32
. A second latch
25
has an output connected to what will be called time-delay device
27
, which has an output which is connected to and controls the state of second switch
17
. Latch
25
is controlled by start and stop lines
31
and
33
.
Latch
24
and time-delay
26
, latch
25
and time-delay control
27
, and switches
16
and
17
control whether multiplexed signal
50
is passed to output
22
, or whether the output of buffer
18
or buffer
19
is passed to output
22
at any given time.
Operation of the embodiment of
FIG. 1
is as follows. Multiplexed signal
50
is essentially an audio signal mixed with periodic data bursts
64
and is presented as an input signal at audio input
12
in FIG.
1
. As stated above, this signal
50
is fed to first input
14
of switch
16
. As illustrated in
FIG. 1
, signal
50
which has been delayed by N/2 sample times is iterated through storage buffer
18
in chunks which are N samples in length, and signal
50
which has been delayed by N sample times is iterated through storage buffer
19
which is also N samples in length. In other words, at any moment in time, a sample from buffer
18
would be N/2 samples times behind signal
50
, and a sample from buffer
19
would be N sample times behind signal
50
and N/2 sample times behind buffer
18
(See
FIG. 3
at
50
,
52
, and
53
).
It is to be understood that in the preferred embodiment the N samples correspond to the number of samples required to completely fill a time period which is slightly longer than a data burst
64
. In the preferred embodiment N samples corresponds to the number of samples required to completely fill 37.5 milliseconds (ms) which is 1.5 ms longer than the data to be removed (a data burst
64
).
The present invention operates at a sampling rate of 8 Khz. Therefore the value N can be calculated according to the following equation.
N
=8,000·samples/
s
·37.5·ms=300
Thus, in one embodiment of the invention, the buffer is 300 samples in length.
Audio output
22
has essentially three options, depending on the state of switches
16
and
17
. One option is audio
12
(multiplexed signal
50
). Another option is the contents of buffer
18
, which trails signal
50
by N/2 sample times. The third option is the contents of buffer
19
, which trails signal
50
by N sample times. As can be understood by the following description, the components cooperate in function and timing to substitute pieces of audio taken from immediately prior to and immediately after a data burst
64
, to replace the data burst and reproduce signal
50
at output
22
without the data burst.
The first option described above simply sends undelayed signal
50
to output
22
. To create the first option, switches
16
and
17
connect respective inputs
14
and
21
to their outputs. The signal path is therefore directly between input
12
and output
22
of FIG.
1
. In this case, switches
16
and
17
are set to positions opposite from what is shown in
FIG. 1
, and will be referred to as “open”.
To create the second option, switch
17
connects input
23
to its output
22
. The state of switch
16
is therefore irrelevant because it is non-conducting at the unselected input
21
of switch
17
. During the second option, the contents of buffer
18
is sent to output
22
. Switch
17
is in what will be called the “default” position, where first input
23
of switch
17
is driven by buffer
18
. Switch
17
is activated through start and stop lines
31
and
33
. These lines pass through latch
25
which latches the output high when a positive-going pulse is detected on start. When a positive-going pulse is present on receipt of the stop instruction, latch
25
resets its output to the low state.
The output of latch
25
is sent through a delay device
27
of M samples in length. This allows the device controlling start and stop lines
31
and
33
to not be synchronized to the actual audio. It is to be understood that this operation assumes that the audio will arrive at the controlling unit to the start and stop lines
31
and
33
before it is present on the audio input
12
of FIG.
1
.
The value of M can be set experimentally or it can be computed by evaluating the system delays, such as can be accomplished by one skilled in the art. An alternate method consists of a separate delay on start and stop lines
31
and
33
as opposed to one delay on the output of latch
25
. This allows what can be called the “replay window” to be widened to be larger than the actual data pulse width.
To create the third option for output
22
, switch
17
is moved from its default to its on position so that its second input
21
is driven by switch
16
. Also switch
16
remains in its default position so that its first input
15
is driven by buffer
19
. Switch
16
is activated through a stop line and a “mid” line, which is set halfway between the start and stop lines (See
FIG. 3
at
55
). The latch
24
and delay
26
operate in the same way as latch
25
and delay
27
.
To assist in understanding operation of delay buffers
18
and
19
, reference can be taken to FIG.
2
. In the preferred embodiment, buffer
18
is 150 samples long and has an associated pointer
34
. Pointer
34
points to the location in the storage buffer that the next audio input sample will be stored. Buffer
18
gets its output from the current location of pointer
34
just before it is overwritten by the next input sample. This output is referred to as the “oldest sample”
36
, or the [N-149] sample.
Thus the output is the oldest sample or the [N-149] sample. Once the sample is stored, pointer
34
is advanced one sample position. This means that the location just before pointer
34
contains what is called the most “recent sample”
38
.
Buffer
19
is the same as buffer
18
except that it is 300 samples long. Therefore, by utilizing a sampling procedure of the analog multiplexed signal, buffers
18
and
19
continuously refresh themselves with the most recent audio sample and purge themselves of the oldest audio sample, in the context of the finite length of N/2 samples and N samples in length respectively. As will become apparent, buffer
18
is only N/2 samples long because it only has to delay signal
50
by N/2 samples, whereas buffer
19
must delay signal
50
by N samples.
By referring specifically to
FIG. 3
, a timing diagram for
FIG. 1
is shown and illustrates how data bursts
64
are replaced with portions of the audio from signal
50
. As previously mentioned, the time-divided multiplexed waveform
50
at the top of
FIG. 3
is what is received at audio input
12
of
FIG. 1
, and the outputs
52
and
53
of buffers
18
and
19
are just delayed versions of signal
50
. These delays are for a period of time generally equivalent to the time of N/2 and N samples respectively, and are related to the characteristics of storage buffers
18
and
19
in the process of storing samples in buffers
18
and
19
. By appropriate selection, the delays can be increased or decreased according to need or desire. Thus the top three signals of
FIG. 3
graphically illustrate the availability of three versions of signal
50
at any given time, each which is shifted in time relative to one another.
FIG. 3
next illustrates how control lines
30
,
31
,
32
,
33
, latches
24
and
25
, and time delays
26
and
27
, control switches
16
and
17
to place certain parts of the three signals
50
,
52
, and
53
at output
22
at different points of time.
It should be noted that start pulse
54
, mid pulse
55
and stop pulse
56
that appear at mid, stop, start and stop lines
31
,
33
,
30
and
32
of
FIG. 1
, are earlier in time than the actual data bursts
64
in signal
50
. Latch
25
generates a pulse signal
58
from start and stop pulses
54
and
56
based on the leading edge of those pulses. Note that start pulse
54
is approximately N/2 samples ahead of data burst
64
in signal
50
and a full N samples ahead of N/2 delayed signal
52
of buffer
18
. Pulse-delay device
27
serves to shift pulse
44
in latch output signal
58
M sample lengths, or so that it generally corresponds and lasts the entire period of data burst
64
in N/2 delayed signal
54
. The resulting shifted pulse
46
of delayed latch output signal
60
controls switch
17
. Prior to pulse
46
of signal
60
, switch
17
would remain in its default state, and would pass signal
52
(signal
50
time-delayed by N/2 ) to audio output
22
. It is important to note that in its normal state, when data bursts
64
are not being replaced with chunks of audio, it is N/2 time delayed signal
52
that is passed to audio output, not original signal
50
. That is, audio comes from the output of storage buffer
18
(in other words, the delayed input signal
52
of
FIG. 3
) not from audio input
12
. See the portion of the ultimate output signal shown at reference number
90
at the bottom of FIG.
3
.
When pulse
46
is generated, switch
17
turns “on” but switch
16
stays in default position. As such, the then contents of buffer
19
are passed to audio output
22
. Because buffer
19
lags buffer
18
by N/2 samples, it essentially replays the immediate preceding N/2 samples of the output of buffer
18
. Thus, as shown at
92
in
FIG. 3
, the next N/2 samples after portion
90
will be a repeat of the previous N/2 samples (see reference numeral
92
). This essentially covers up or replaces approximately one-half of what otherwise would a data burst
64
in signal
52
.
As can be seen in
FIG. 3
, latch
26
output (signal
62
), is N/2 samples in length and is time-shifted by M samples so that it essentially lines up with the last one-half of data burst
64
of signal
52
. This is accomplished by beginning pulse
48
at the midpoint of pulse
44
and then delaying it the same M samples (see reference numeral
49
) as pulse
44
was delayed.
Pulse
49
controls the state of switch
16
by changing it from its default position (where it is driven by buffer
19
) to an “on” position, where it passes original signal
50
. Because pulse
49
is in the second half of data burst
64
of signal
52
, the essentially N/2. samples of audio immediately succeeding data burst
64
in signal
50
are passed to audio output
22
(see reference numeral
94
in FIG.
3
), and what otherwise would be a disruptive second half of data burst
64
in N/2 time delayed signal
52
, is now completely replaced with audio (See parts
90
,
92
,
94
,
96
of signal
66
).
After pulse
49
, switches
16
and
17
revert to default positions, and the signal to audio output
22
is again N/2 time delayed signal
52
(see reference numeral
96
in FIG.
3
). Note that during data burst
64
of signal
52
, switch
17
is “on” the full time and switch
16
is on the last half of that time, and audio comes first from N time delayed signal
53
(for the first half pulse
46
), and then from undelayed signal
50
(for the last one half of pulse
46
as well as the whole duration of pulse
49
). Therefore, what otherwise would have been data burst
64
of signal
52
is replaced by a replay of the immediate past audio of signal
52
(cut and pasted from signal
53
) and by a premature play of the immediate succeeding audio of signal
52
(cut and pasted from signal
50
). The audio at other times comes from signal
52
of FIG.
3
. The resultant audio output on output
22
of switch
17
is shown by signal
66
in FIG.
3
. Discontinuities
65
,
67
and
69
near the transitions of the replayed portions
92
and
94
of audio output
66
can be smoothed with an optional low-pass filter (not shown). Lengthening of the window defined by pulses
46
and
49
of the delayed output devices
26
and
27
can be performed, as discussed earlier, so that there is some tolerable error in the location of data burst
64
relative to delayed latch output pulses
46
and
49
.
Any discontinuities in the audio output can be smoothed with the use of a weighting function. The weighting function can be derived from any standard windowing function (Fourier window) well known to those skilled in the art, such as for example the triangular (Bartlett) window, the raised cosine (Hanning) window, or the Hamming window. The most basic weighting function is derived from the rectangular window, and is the function used in FIG.
3
. The rectangular window and the weighting functions derived from it are shown in FIG.
4
. The rectangular window does not smooth the discontinuities. Another possible window, the Bartlett window, and its weighting functions are also shown in FIG.
5
. The Bartlett window smoothes the discontinuities between the “past” and “future” replacements.
As can be seen in
FIG. 3
at audio output
66
, replayed audio segment
92
and pre-played audio segment
94
are essentially identical reproductions of the immediately preceding and immediately succeeding portions of the signal. Stated a different way, when combined, portions
92
and
94
are intentionally selected to be slightly longer in length than data pulse
64
of signal
52
, and thereby conceal the data pulse
64
in the audio output
66
. Furthermore, by dividing the time otherwise taken by burst
64
and by replacing one-half with audio portion
92
repeating the immediate preceding audio, and replacing the other one-half with audio portion
94
pre-playing the immediate succeeding audio, better audio reproduction can occur at the receiver. Instead of a whole N-samples-in-length audio replay like described in U.S. Ser. No. 08/689,397, which can degrade the audio somewhat, N/2 duplications of the real audio make the audio reproduced of better quality.
The included preferred embodiment is given by way of example only, and not by way of limitation to the invention, which is solely described by the claims herein. Variations obvious to one skilled in the art will be included within the invention defined by the claims.
For example, the operation of the various components diagrammatically depicted in
FIG. 1
can be implemented in hardware, firmware, or substantially in software. As previously mentioned, a significant amount of the operation can be implemented in a digital signal processor.
FIG. 6
illustrates a software simulation of the embodiment shown and described with respect to
FIGS. 1-3
.
Claims
- 1. A method of concealing data bursts in an analog transmitted time multiplexed signal comprising periods of audio and periods of said data bursts comprising: passing said audio in said analog transmitted time multiplexed signal to an output during periods of audio in said signal;during periods of said data bursts in said signal, passing stored audio to said output therefore replacing at the output said data bursts with audio, the stored audio comprising a portion of the immediately prior audio and a portion of the immediately future audio.
- 2. The method of claim 1 wherein the stored audio is taken from the set comprising audio immediately prior to a data burst and audio immediately after a data burst.
- 3. The method of claim 1 wherein the step of replacing at the output said data bursts comprises storing immediately past and future audio samples from the multiplexed signal and replaying the immediately past and future audio samples during each data burst.
- 4. The method of claim 3 wherein the storage of the immediately past and future audio samples is correlated to the length of a data burst.
- 5. The method of claim 4 wherein the data bursts are of a length that is generally less than a spoken syllable.
- 6. The method of claim 3 further comprising constantly replenishing the stored immediately past and future audio samples.
- 7. A method of concealing data bursts in an analog transmitted time multiplexed signal comprising periods of audio and periods of said data bursts comprising:replacing a said data burst in said analog transmitted time multiplexed signal with audio samples, one taken from immediately prior to the data burst and one taken from immediately after the data burst.
- 8. The method of claim 7 wherein the step of replacing at the output a data burst comprises storing immediately past future audio samples in the multiplexed signal and replaying the immediately past and future audio samples during the data burst.
- 9. The method of claim 7 further comprising utilizing a weighting function to smooth transitions caused by the replacing step.
- 10. An apparatus for concealing data bursts in the output signal of a descrambler of an analog transmitted time multiplexed signal comprising periods of scrambled audio and periods of said data bursts comprising:a first storage buffer which holds successively iterated time delayed audio samples of said analog transmitted time multiplexed signal; a second storage buffer which holds successively iterated time delayed audio samples of said signal, the time delay exceeding that of the first storage buffer; first and second switching devices; a first signal pathway from the first storage buffer, to the first switching device and to an output; a second signal pathway from the second storage buffer to the second switching device to the first switching device and to the output; a third signal pathway from said signal to said second switching device to said first switching device to the output; a control device to control said and second switching devices between said first, second and third signal pathways; so that in a first state, the first signal path is presented, until at or near the arrival of a data burst, at which time a second state of the second signal path is presented which repeats a portion of non-data burst signal, after which a third state of the third signal path is presented which pre-plays a portion of non-data burst signal, to conceal the whole data burst from the output.
- 11. The apparatus of claim 10 further comprising a latch connected to each control device.
- 12. The apparatus of claim 10 further comprising a time delay device to delay operation of each switch for a pre-selected time.
- 13. An apparatus to conceal data bursts in an analog audio waveform with periodic data bursts of a length in an analog descrambler comprising:an input to receive the said analog audio waveform and an output to transfer the waveform to a speaker; a switching device having a three states, a first state to select and pass those portions of the waveform without periodic data bursts to the output, a second state to select and pass a repeated portion of the waveform in replacement of a portion of the data burst, and a third state to select and pass a pre-played portion of the waveform in replacement of another portion of the data burst; a control device connected to the switching device to control said three states of the switching device, so that repeated and pre-played portion of the waveform and not a data burst are sent to output during a data burst.
- 14. A method of suppressing encoded data bursts in an otherwise unencoded analog signal comprising:passing unencoded portions of the analog signal to an output; replacing data bursts with samples of the unencoded analog signal, one sample taken from immediately prior to the data burst and one sample taken from immediately after the data burst.
US Referenced Citations (30)
Foreign Referenced Citations (1)
Number |
Date |
Country |
57-113647 |
Jul 1982 |
JP |