GB2166027A - A speech transmission device - Google Patents
A speech transmission device Download PDFInfo
- Publication number
- GB2166027A GB2166027A GB08525168A GB8525168A GB2166027A GB 2166027 A GB2166027 A GB 2166027A GB 08525168 A GB08525168 A GB 08525168A GB 8525168 A GB8525168 A GB 8525168A GB 2166027 A GB2166027 A GB 2166027A
- Authority
- GB
- United Kingdom
- Prior art keywords
- switching
- level control
- signal
- automatic level
- transmission device
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 230000005540 biological transmission Effects 0.000 title claims abstract description 20
- 230000003321 amplification Effects 0.000 claims abstract description 7
- 238000003199 nucleic acid amplification method Methods 0.000 claims abstract description 7
- 238000009877 rendering Methods 0.000 claims abstract description 3
- 230000005669 field effect Effects 0.000 description 8
- 239000003990 capacitor Substances 0.000 description 4
- 230000003292 diminished effect Effects 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers
- H03G3/20—Automatic control
- H03G3/30—Automatic control in amplifiers having semiconductor devices
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G1/00—Details of arrangements for controlling amplification
- H03G1/04—Modifications of control circuit to reduce distortion caused by control
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M3/00—Automatic or semi-automatic exchanges
- H04M3/42—Systems providing special services or facilities to subscribers
- H04M3/56—Arrangements for connecting several subscribers to a common circuit, i.e. affording conference facilities
- H04M3/568—Arrangements for connecting several subscribers to a common circuit, i.e. affording conference facilities audio processing specific to telephonic conferencing, e.g. spatial distribution, mixing of participants
- H04M3/569—Arrangements for connecting several subscribers to a common circuit, i.e. affording conference facilities audio processing specific to telephonic conferencing, e.g. spatial distribution, mixing of participants using the instant speaker's algorithm
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M9/00—Arrangements for interconnection not involving centralised switching
- H04M9/08—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic
- H04M9/10—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic with switching of direction of transmission by voice frequency
Landscapes
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Interconnected Communication Systems, Intercoms, And Interphones (AREA)
Abstract
A speech transmission device having voice-activated switching of amplification and automatic level control means following the comparator which performs the voice switching, includes circuit means (31 . . . .42) for rendering ineffective the automatic level control of the signal in the path to the comparator when switching is not in favour of that signal and for allowing the automatic level control to be effective when switching is in favour of that signal. The reinstatement of the automatic level control consequent upon switching in favour of the signal is in such a manner that the switching remains in favour of the signal after the automatic level control and in such a manner as to avoid a subjectively large burst of sound at such switching. <IMAGE>
Description
SPECIFICATION
A speech transmission device
This invention relates to a speech transmission device and it relates more especially to a speech transmission device having voice-activated switching of amplification.
Speech transmission devices having voiceactivated switching of amplification are known.
Such devices find especial use in loudspeaking telephones, line amplifiers and telephone systems whereby multiple telephone users are placed in contact with each other for the purposes of a telephone conference. In some of the known speech transmission devices having voice-activated switching of amplification, automatic level control of a signal is employed before the signal reaches a comparator and voice-switched amplifier. The signal fed to the comparator is thus reduced by the automatic level control and the ability of the signal to compete for control of the switching is undesirably diminished.
It is an aim of the present invention to obviate or reduce the above mentioned problem.
Accordingly, this invention provides a speech transmission device having voice-activated switching of amplification, which speech transmission device comprises automatic level control means, comparator means, voiceswitched amplifier means, and circuit means for rendering ineffective the automatic level control of a signal in a path to the comparator when switching is not in favour of that signal and for allowing the automatic level control to be effective when switching is in favour of that signal, the reinstatement of the automatic level control consequent upon switching in favour of the signal being in such a manner that the switching remains in favour of the signal after the automatic level control and in such a manner as to avoid a subjectively loud burst of sound at such switching.
The speech transmission device may have any number of separate channels for incoming and outgoing signals, each incoming channel comprising the automatic level control means, voice-switched amplifier means and circuit means specified above.
Preferably, the circuit means forms a bypass path which in use bypasses the automatic level control path whilst the voice switching is activated against the signal.
The circuit means may include a speech gate which is normally open but which is closed when the signal has acquired control of the voice switching and which remains closed until the control has been relinquished.
The loss or gain of the bypass path when the speech gate is open is preferably substantially the same as that of the automatic level control path at low levels at which the automatic level control is inoperative.
The output from the bypass path and the output from the path of the automatic level control may be arranged to come together in such a way that only the larger output is fed to the comparator or to the comparator and the voice-switched amplifier means.
The channels for incoming and outgoing signals may be combined by additional means for two-wire purposes.
If desired, there may be only two incoming and only two outgoing channels.
Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which:
Figure 1 shows a known automatic level control path for a signal;
Figure 2 shows the automatic level control path of Figure 1 but modified in accordance with the invention with circuit means forming a bypass path for bypassing the original automatic level control path;
Figure 3 illustrates a speech transmission device in the form of one incoming channel of a conference amplifier employing unilateralization of speech; and
Figure 4 shows a modification of the circuit shown in Figure 3.
Referring now to Figure 1, a known speech transmission device having voice-activated switching of amplification is such that a signal on input path 2 is subject to automatic level control before it reaches an output path 4 leading to a comparator and voice-switched amplifier (not shown). The signal fed to the comparator is thus reduced by the automatic level control and the ability of the signal to compete for control of the switching is undesirably diminished.
Referring now to Figure 2, it will be seen that additional circuit means have been provided, the circuit means forming a bypass path 6. The bypass path may be regarded as a signal attack path in which the signal is not subject to the automatic level control reduction as occurs with Figure 1. The bypass path 6 should have substantially the same loss or gain as the automatic level control path 8 when the automatic level control is inoperative. Both paths 6,8 receive the same input via the input path 2. The bypass path 6 is provided with a speech gate 10 which is open whilst the voice-activated switching is switched against the signal under consideration. The bypass path 6 and the automatic level control path 8 reunite as illustrated in an over-ride arrangement 12 at their outputs.The over-ride arrangement 12 is such that only the larger of the two outputs is passed on to the comparator, or to the comparator and the voice-switched amplifier means via paths 4 and 14. The signal may pass to the voiceswitched amplifier via path 16 instead of path
14.
A signal large enough to work the automatic level control passes initially via the bypass path 6 and, if large enough compared with other signals fed to the comparator to initiate switching in its favour, then a control signal from the voice-switching stages of the voiceswitched amplifier means closes the speech gate 10 in the bypass path 6 and the automatic level control path 8 then takes over the role of passing the signal to the comparator.
The switching hysteresis in the voice-activated switching ensures that the switching remains in favour of the signal received by the comparator, which is now reduced by virtue of the automatic level control.
Eventually, when a different signal in another channel (not shown) takes control of the voice-activated switching, the voice-activated switching again opens the speech gate 10 in the bypass path 6 to give once again full advantage of attack to fresh signals in the channel under consideration.
Referring now to Figure 3, there is shown one incoming channel of a conference amplifier employing unilateralization of speech. In
Figure 3 there is shown below the broken line 21,22 in block form part of the circuit of an existing design of telephone conference amplifier. This existing design is British Telecom conference combining unit SA 20286 and it uses the technique of speech unilateralization for voice switching as described in United
Kingdom Patent Nos. 1131947, 1395496 and
1565200. Above the broken line 21, 22 there is shown additional circuit means forming part of the present invention.
In the existing design, an incoming signal 23 goes via a terminal 24 through a gain controlled amplifier 25. The incoming signal 23 is made positive-going in a unilateralizer 26 and the signal then passes, via a diode 27 and a terminal 28, to the remainder 29 of the conference amplifier circuit. The remainder 29 of the conference amplifier circuit includes a comparator, a voice-activated switching device, and a switched amplifier. The gain of the amplifer 25 is controlled by the output of a detector 30 which receives its input as illustrated from the output of the unilateralizer 26.
In the bypass circuit according to the invention illustrated above the broken line 21,22 there is provided an input path resistor 31 which is connected from the terminal 24 to the inverting input of an operational amplifier 32. The operational amplifier 32 has its noninverting input connected to the central supply rail 42 of a balanced power supply for the operational amplifier 32 and for the existing circuit. From its output to its input, the operational amplifier 32 has two negative feedback paths, one via a diode 33 and a resistor 34 in series, and the other path via a diode 35 and a resistor 36 in series. The cathode of the diode 33 and the anode of the diode 35 are connected to the output of the operational amplifier 32.
A capacitor 37 is connected between the junction of the diode 33 and the resistor 34 and the central supply rail 42. The time constant of the resistor 34 and the capacitor 37 is arranged to be the same as the decay time constant of the detector of the unilateralizer 26. To point 40, the junction of the diode 35 and the resistor 36, is connected the anode of a diode 38. The cathode of the diode 38 goes to the terminal 28 of the existing circuit.
A control wire 41 from the voice-activated switching elements in the remainder 29 of the conference amplifier circuit is applied to the gate of a field effect transistor 39 which has source and substrate connected to the inverting input of the operational amplifier 32 and drain connected to the point 40.
The bypass circuit advantageously operates to produce a positively unilateralized signal at the point 40. Furthermore, the bypass circuit is economical in its use of components. During operation of the bypass circuit, via the diode 33, the capacitor 37 is negatively charged from the operational amplifier 32 at positive-going peaks of signal input to the resistor 31. The voltage across the capacitor 37 follows the envelope of the incoming signal and is applied to the resistor 34. For most of the time, the configuration now acts as an adder, with a negative-going envelope component being input to the operational amplifier 32 via the resistor 34, and a signal component being input to the operational amplifier 32 via the resistor 31.The resulting output at the point 40 is a positive-going precisely unilateralized form of the incoming signal so long as the field effect transistor 39 is switched off. The control to the gate of the field effect transistor 39 is such that the field effect transistor 39 is switched off when the voice-activated switching elements are switched against the signal incoming on this channel.
The gain via the bypass path, with the field effect transistor 39 switched off, between the terminals 24 and 28, is, for reasons concerned with tolerances of components, arranged to be slightly less than the low level gain between these points via the automatic level control path, with the automatic level control being inoperative. Thus, signals small enough not to work the automatic level control pass to the remainder 29 of the conference amplifier circuit initially via the automatic level control path and the lower level via the bypass path has no affect.
When a signal coming to the remainder 29of the conference amplifer circuit via the automatic level control path at low levels, or via the bypass path, initiates the voice-activated switching to switch in favour of the incoming signal 23, the control wire 41 switches the field effect transistor 39 on, the bypass path becomes inoperative, and the signal to the remainder 29 of the conference amplifier circuit is sustained via the automatic level control path and is thus properly moderated.
The voice-activated switching elements remain switched with the reduced level of signal by virtue of the switching hysteresis.
When a signal incoming to one of the other channels takes control of the voice-activated switching, the control wire 41 switches the field effect transistor 39 off and the bypass path is once again opened to deal with a renewal of the incoming signal 23.
The diode 38 is employed to avoid feeding through the resistor 36 to the input of the operational amplifier 32 other positive-going voltages which appear at the terminal 28.
If desired, the diode 38 may alternatively be connected directly to the output of the operational amplifier 32 instead of to the point 40.
This is to compensate for the voltage drop across diode 38 and thus to avoid the conseguent loss of switching sensitivity at moderate levels at which this drop is important. Such a modified circuit is shown in Figure 4 wherein similar parts as in Figure 3 have been given the same reference numerals. In Figure 4, it will be seen that a resistor 43 is connected between the point 40 and the central supply rail 42. Also, a diode 44 is connected to the field effect transistor 39 as shown. The noninverting input of the operational amplifier 32 is connected to line 45 which connects to a point siightly negative relative to the central supply rail 42.
It is to be appreciated that the embodiments of the invention described above have been given by way of example only and that modifications may be effected.
Claims (7)
1. A speech transmission device having voice-activated switching of amplification, which speech transmission device comprises automatic level control means, comparator means, voice-switched amplifier means, and circuit means for rendering ineffective the automatic level control of a signal in a path to the comparator when switching is not in favour of that signal and for allowing the automatic level control to be effective when switching is in favour of that signal, the reinstatement of the automatic level control consequent upon switching in favour of the signal being in such a manner that the switching remains in favour of the signal after the automatic level control and in such a manner as to avoid a subjectively loud burst of sound at such switching.
2. A speech transmission device according to claim 1 in which the circuit means forms a bypass path which in use bypasses the automatic level control path whilst the voice switching is activated against the signal.
3. A speech transmission device according to claim 2 in which the circuit means includes a speech gate which is normally open but which is closed when the signal has acquired control of the voice switching and which remains closed until the control has been relinquished.
4. A speech transmission device according to claim 3 in which the loss or gain of the bypass path when the speech gate is open is substantially the same as that of the automatic level control path at low levels at which the automatic level control is inoperative.
5. A speech transmission device according to any one of claims 2 to 4 in which the output from the bypass path and the output from the path of the automatic level control are arranged to come together in such a way that only the larger output is fed to the comparator or to the comparator and the voiceswitched amplifier means.
6. A speech transmission device according to any one of the preceding claims in which the channels for incoming and outgoing signals are combined for two-wire purposes.
7. A speech transmission device according to claim 1 and substantially as herein described with reference to Figures 2 and 3 or
Figures 2, 3 and 4 of the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB848426581A GB8426581D0 (en) | 1984-10-19 | 1984-10-19 | Speech transmission device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8525168D0 GB8525168D0 (en) | 1985-11-13 |
| GB2166027A true GB2166027A (en) | 1986-04-23 |
Family
ID=10568493
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB848426581A Pending GB8426581D0 (en) | 1984-10-19 | 1984-10-19 | Speech transmission device |
| GB08525168A Withdrawn GB2166027A (en) | 1984-10-19 | 1985-10-11 | A speech transmission device |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB848426581A Pending GB8426581D0 (en) | 1984-10-19 | 1984-10-19 | Speech transmission device |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8426581D0 (en) |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB703801A (en) * | 1951-11-19 | 1954-02-10 | Leonard Ernest Ryall | Improvements in or relating to voice switching in telephone transmission systems |
-
1984
- 1984-10-19 GB GB848426581A patent/GB8426581D0/en active Pending
-
1985
- 1985-10-11 GB GB08525168A patent/GB2166027A/en not_active Withdrawn
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB703801A (en) * | 1951-11-19 | 1954-02-10 | Leonard Ernest Ryall | Improvements in or relating to voice switching in telephone transmission systems |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8525168D0 (en) | 1985-11-13 |
| GB8426581D0 (en) | 1984-11-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |