US2271000A - Speech transmission system - Google Patents

Description

Jan. 27, 1942. w. v. LovELL SPEECH TRANSMISSION SYSTEM 2 Sheets-Sheet 1 Filed Jan. 7, 1941 WEST 5 BJ Law 6 e2 7 2.a f@ mn OWU f j ,sA n

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SPEECH TRANSMISSION SYSTEM Filed Jan. '7; 1941 2 Sheets-Sheet 2 /Nl/E/VTOR W V LOVE L L '9s/KMA A T TORNE V Patented Jan. 27, 1942 UNITED STATES PATENT OFFICE SPEECH TRANSMISSION SYSTEM William v. Lovell, Sanford, Fia.. Application January 7, 1941, Serial No.`3'73,395

11 Claims.

The invention relates to a speech transmission system.

An object of the invention is to achieve increased efficiency in the operation of certain'types of speech transmission systems.

A further object of the invention is the transmission of messages in such a manner that intelligible reception of the message by unauthorized persons will be rendered very diflicult.

A more specic object of the invention is to decrease the idle time of speech transmission circuits. v

-It is recognized by transmission engineers that, during a so-called conversation period on a four- Wire circuit, one side of the circuit is actually in use only about one-third of the time. `It has previously been proposed to take advantage of this fact by associating a number of subscribers telephone circuits with a lesser number of oneway speech channels and switching each different speech portion of vocal interval duration occurring in the various' subscribers circuits to any one of the channels that happens to be idle at a particular moment. While such systems appear, in general, to provide worthwhile advantages particularly from an economic standpoint, there has been some objection to the use of such an arrangement on high quality circuits due both to the fact that distortion may creep in because of the switching operations and to lthe fact that small portions of the transmission may be lost or delayed at times due to momentary lack of an idle channel. v

A feature of the present invention resides in means whereby only a selected circuit is switched about from idle channel to idle channel, thev other circuits operating over their individually assigned channels.

In accordance with a specific embodiment of the invention, a given number, such as three, west-east and a corresponding number, such as three, east-west channels are provided for connecting, in the illustrative case, three subscriber stations at the west terminal of a speech transmission system with three subscriber stations at the east terminal for two-way conversations. y

wanted by the subscriber normally assigned thereto such subscriber will take over the channel and the circuit of the fourth subscriber will be switched onto the next idle channel. Should all channels be in use by the preferred stations, interconnection of the fourth pair of subscriber stations will be delayed until an idle channel is available.

The above arrangement results in eiicient and economical operation of the system as six oneway channels provide the service ordinarily provided by eight such channels and yet there is no necessity of switching the high quality circuits from one channel to another with consequent possibility 'of delayed transmission. It is contemplated that the switched circuit may, if desired, be vof the type ordinarily termed a low quality circuit wherein a small amount of `distortion or occasional delays will not'be' objectionable. Such a circuit Vmay be utilized, for example, by Aattendants supervising the operation of the system. f

It will be apparent that a measure of privacy will be attained by the 'arrangement described inasmuch as an unauthorized person listeningin on any of the channels between the terminals will hear snatches of two different conversations interspaced one with the other; i. e., the normal conversation of the channel and the switched conversation. A somewhat higher degree of privacy will be attained, of course, with respect to the switched conversation as snatches of this conversation will appear on different n channels.

invention; and

Fig. 2 shows in detail the switching arrangement of one terminal of the system of Fig. 1.

Referring now to the drawings, there is il-l lustrated diagrammatically in Fig. 1, two terminals of a two-way telephone system which may be, for example, a two-way radio or line Wire telephone system. Four subscriber sets, Il, I2, I3 and I4, are shown at the west terminal each of which is provided' with a suitable two-wayl subscribers telephone circuit; similarly, four subscriber sets, I5, I6, I1 and 2 I, are shown at the east terminal, each of these sets also being provided with a suitable two-way subscribers telephone circuit.

The west terminal switching apparatus'is represented by box 22 and the east terminal switching apparatus by box 23; these switching arrangements will be described in detail subsequently in connection with Fig. 2.

A west-east channel 24 and an east-west channel 25 are provided for two-way conversations between subscriber W-I and subscriber E--I, the arrangement being such that channel 24 is immediately available to subscriber W-I whenever a speech portion of vocal interval duration is produced by his subscriber set II and that channel 25 is immediately available to subscriber E--I whenever a speech portion of vocal interval duration is produced by his subscriber set I5. Similarly, west-east channel 26 and east-west channel 21 are provided for two-way conversations between subscribers W-2 and E2 and west-east channel 4|` and east-west channel 42 are `provided for two-way ,conversations between vsubscribers W-3 and E--3.

It will be observed that conversations between subscribers W-I, W-2 and W'-3 and subscribers E-I, E-2 and E-S, respectively, are maintained on a preferred or high quality basis as the terminal circuits are not switched from channel to channel. However, in accordance with the arrangement, a secondary service is provided for two-way conversations between a fourth subscriber W--4 at the west terminal and la fourth subscriber E-4 at the east terminal. It is contemplated that such additional facility might well be utilized by an attendant supervising the operation of the high quality circuits in which case slight distortion or occasional delay would be particularly serious. As indicated schematically, transmission from subscriber set I4 to subscriber set 2l is achieved by switching the terminal circuits about among channels 24, 26 and 4|, depending upon which is idle at any one moment while transmission from subscriber set 2| to subscriber set I4 is achieved by similarly switching the terminal circuits about among ` channels 25, 21 and 42. q

When voice frequency currents originating at subscriber set I4 are applied to any of the westveast channels, a distinctive tone of low frequency produced by source 43 is applied to the same channel; similarly when voice frequency currents originating at subscriber set 2| are applied vto any of theeast-west channels a low frequency tone produced by source 44 is applied tothe same channel. 'The purpose of these tones will be described subsequently in reference to Fig. 2.

The general switching arrangement contemplated is such that, so far as transmission from subscriber W4 to subscriber E-4 is concerned, channel 24 is superior (i. e. preferred) to ` channels 26 and 4| and channel 26 is superior to channel 4I. That is, speech currents originating kat subscriber set I4 are always applied `to channel 24 so long as channel 24 is not in use for transmission from W--I to lll-I. Should channel 24 be in use, the speech currents originating at subscriber set I4 are applied to channel 26 so long as channel 26 is not in use for transmission from vW--2 to E-,2. Shculdlboth channels `24 and 26 be in use, the speech currents of subscriber set `I4 4are then applied to channel .4I so long as channel 4I is not in use for transmission from W-B .to E-3.

Should all three channels be in use, transmission of the speech currents of subscriber set I4 is delayed until one of the channels becomes idle.

In like manner with respect to transmission from E-4 to W-4, channel 25 is superior to channels 21 and 42 and channel 21 is superior to channel 42.

The term vocal interval as used herein means the duration of one or a succession of syllables no one of which is separated from the preceding syllable by an interval as great as the hangover time of the system,weak beginnings and endings, i. e., portions not capable of causing relay operation, being considered parts ofthe silent interval. Hang-over time is a term commonly used in connection with systems including voiceoperated devices and means theperiod that a voice-operated device remains, due to its own characteristics, in operated position after the operating impulse has been removed.

Referring now'to Fig. 2, a detailed showing is set forth of the switching apparatus of the west terminal represented in Fig. 1 by box 22.

Subscriber set II is coupled to transmitting line 14 and receiving line 15 by transformer 16, network 11 serving to provide proper balance in the well-known manner. In a similar manner, subscriber set I2 is connected to transmitting line 8| and receiving line 82 through transformer 83, subscriber set I 3 is connected to transmitting line '84 and receiving line 85 through transformer 06 and subscriber set I4 is connected to transmitting line' 81 and receiving line IOI through transformer |02.

For purposes of further illustration of the invention, the operation of the circuits of Fig. 2 will now be described in detail. Let us assume, first, that subscriber W-I speaks, at which time speech energy originating at subscriber station II will be applied through transformer 16 to transmitting line 14. As the speech energy is delayed somewhat in its passage through delay `device |03, let us rst see what operations result from passage of a part of the speech energy through amplifier-detector |04.

The rectified and filtered speech currents emanating from amplifier-detector |04 cause operation of relays |05 and |06. Operation of relay |06 connects, through its front contacts, `transmitting line 14 to channel 24 so that the speech energy after traversing delay device |03 is sent out over channel 24. Operation of relay |05 interrupts at its back contacts ther connection of transmitting line 81 of subscriber set I4 to vline |01 and connects, at its front contacts, transmit ting line 81 to line I I I. f

The speech energy passing out over channel 24 is received by subscriber E--I of the east ter- As the .east terminal equipment has not been illustrated let us refer for the moment to the receiving equipment of the west terminal and assume that speech energy is being received from the distant terminal over channel 25. Low-pass filter II2 prevents passage of the high frequency voice currents into path lI I3 ,so that vrelay I I4 remains in normal, unoperated position. The speech energy, therefore, passes through the back contacts of relay I I4 to receiving line 15 and over this line to subscriber set I I.

Returning now to consideration of the transmittingportions of the circuit, let us assume that with v subscriber W-I still talking, ,subscriber W-4 also starts talking, and that Aneither :sub-

called that relays |05 and |06 are in yoperated position due to the fact that subscriber W-I is talking.

Speech energy `produced by subscriber set vI4 is applied to transmitting line 81 vthrough transformer |02, a part of the energy passing through amplifier-detector H and causing operation of relay H6. Operation of relay H6 completes a path through its front contacts over which a low frequency tone produced by source 43 is applied to line 81. We now have on line 81, therefore, both the speech currents of voice frequency and the characteristic toney of low frequency. High-pass filter I I1 serves to exclude the low frequency tone currents from the operating circuit of relay I|6.

Relay |05 being in operated position, as set forth above, the voice frequency currents and tone signals impressed on line 81 are applied through the front contacts of relay |05 to line III and in turn through the back contacts of vrelay |32, which is in unoperated position, to

line |33. As line |33 is connected to channel 26, the voice frequency signals and the tone signals originating at subscriber station I4 are now impressed on channel 26 for transmission to the east terminal.

The currents impressed on channel 26 are received by subscriber E-4 at the east terminal. As the equipment of the east terminal has not been illustrated let us assume for the moment that voice frequency currents and the charac-v teristic low frequency tone are being received over channel 21. The tone signals are of a suiiiciently low frequency to be passed by low-pass lter |34 and are, therefore, impressed on amplifier-detector |35. The energy emanating from amplifier-detector |35 causes operation of relay |36. Operation of relay |36 is effective to interrupt at its back contacts the connection of channel 21 and receiving line 82 and to complete at its front contacts the connection of channel 21 to receiving line IOI. The voice frequency currents incoming over channel 21 are received therefore by subscriber set I4. If desired, a highpass lter may be included in the receiving path in order to exclude any part of the tone signals therefrom.

Returning now to consideration of the transmitting end of the system, it is believed that it will be clear from the above how the arrangement will function with'other combinations of talkers. For example, under the conditionsv described above, i. e., with W-I and W-4 talking, should subscriber W-2 also start talking, the trans- 'mitting path of subscriber W-4 will be transferred from channel 26 to channel 4| by operation of relay |32, relay |31 being in unoperated position as subscriber W-3 is not talking. However, should all three of the preferred subscribers, W-I, W-2 and W--3, be talking, transmission from W-4 will be delayed until an idle channel is available.

Considering again the situation iirst described, i. e., with subscribers W-I and W-4 talking, should subscriber W-I stop talking relays |05 and |06 will drop back to unoperated position and transmitting line 81 of subscriber W-4 will now be connected over line |01 to channel 24 and the Avoice frequency currents and the tone signals Will reachthe east terminal over channel 24, In order to make clear the action of the receiving equipment let us assume that the voice frequency currents and tone signals produced by the subscriber set corresponding to set I4 are now received over channel 25. The low frequency tone currents are passed by low-pass filter H2 and impressed on amplifier-detector |4I. The energyl emanating from amplifier-detector I4! causes operation of relay H4 which results, in turn, in the transfer of channel from receiving line 15 to receiving line |0I. The voice frequency currents are received therefore by subscriber set I4.

It is believed it will be clear from the above that the speech currents and tone signals originating at subscriber set I4 are impressed on channel 24 if subscriber W-I is not talking; on channel 26 if subscriber W-I is talking and subscriber W-Z is idle; on channel 4I `if subscribers W-I and W-2 are talking and subscriber W-3 is idle; and that transmission from set I4 is delayed in the event that all three preferred subscribers are talking. It will be clear also, with respect to the receiving arrangement, that incoming channel 42 is normally connected to the receiving equipment of subscriber set |3, channel 21 is normally connected to the receiving equipment of subscriber set I2 and channel 25 is normally connected to the receiving equipment of subscriber set II. In the event, however, that the low frequency tone originating at the fourth or switched subscriber set is present on a channel, said channel is switched to the receiving equipment of subscriber set |4 which'is the fourth or switched set of the West terminal.

While a specific embodiment of the invention has been selected for detailed description it will be understood that the invention is not `limited in its application to the embodiment described. It will be apparent, for example, that otherl combinations of subscriber sets may be provided. For example, one switched subscriber set may be associated with a larger number of preferred subscriber sets than the three illustrated. 'I'he embodiment described should be taken as illustrative of the invention and not as restrictive thereof. f

What is claimed is:

'1. In a speech transmission system including an east terminal and a west terminal, a plurality of transmitters at the east terminal, a corresponding number of receivers at the West terminal, a corresponding number of speech transmission channels connecting said east terminal and said west terminal, means operated by energy caused by production of a speech fragment of vocal interval duration by one of said transmitters for connecting the output of said transmitter to the speech transmission channel associated therewith, an additional transmitter at said east terminal, a corresponding additional receiver at said west terminal, means controlled by voice energy vfor connecting the output of said additional transmitter to the transmitting end of one of said speech transmission channels, and means controlled over said last-mentioned channel for connecting said additional receiver to the receiving end of the same channel.

2. In a speech transmission system including an east terminal and a west terminal, a, plurality of transmitters at the east terminal, a corresponding number of receivers at the west terminal, a corresponding number of speech transmission channels connecting said east terminal and said west terminal, means effective in response to production of a speech fragment of vocal interval duration byl one of said transmitters for connecting the output of said transmitter to a predetermined one of'said speech transmission channels, an additional transmitter at said east terminal, a distinctive frequency tone source at said east terminal, an additional receiver'at said west terminal, means operated by energy caused by production of a speech frag'- tional' transmitter for connecting the outputs of said transmitter and of said tone source tothe transmitting end of one of said speech transmission channels which is then idle so far as transmission by said plurality of transmitters is concerned, and means controlled by said distinctive tone for connecting said additional receiver to the receiving end of the same channel.

3. In a speech transmission system including an east terminal and a west terminal, a plurality of transmitters at the east terminal, a corresponding number of receivers at the west terminal, a corresponding number of speech transmission channels connecting said east terminal and said west terminal, means operated by energy caused by production of a speech fragment of vocal interval duration by one of said transmitters for connecting the output of said transmitter to one of said speech transmission channels, an additional transmitter at said east terminal, means for connecting the output of said additional transmitter to one of said channels not in use at the time, and means operated by energy resulting from application to said last mentioned channel of a speech fragment of vocal interval duration by one of said plurality of transmitters for transferring the output of said additional transmitter to another of said channels not in use at the time.

4. In a speech transmission system including an east terminal and a west terminal, a first transmitter, a `second transmitter and a third transmitter at said east terminal, corresponding `first, second and third receivers at said west terminal, a first speech transmission channel between said first transmitter and said first receiver, a second speech transmission channel between said second transmitter and said second receiver, and 'a third speech transmission channel between said third transmitter and said third receiver, a fourth transmitter at said east terminal, a fourth receiver at said west terminal, means for connecting the output of said fourth transmitter to said rst channel, and means operated by energy caused by production of a speech fragment of vocal interval duration by said first transmitter for connecting the output of Said first transmitter to said first channel and for transferring the output of said fourth transmitter to said second channel.

5. In a speech transmission system including an east terminal and a west terminal, a first transmitter, a second transmitter and a third transmitter at said east terminal, corresponding first, second and third receivers at said west terminal, a first speech transmission channel between said rst transmitter and said first receiver, a second speech transmission channel between said second transmitter. and said second receiver and a third speech transmission channel between said third transmitter and said third receiver, a fourth transmitter at said east terminal, a fourth receiver at said west terminal, means for connecting the output of said fourth transmitter to said first channel, means operated by energy caused by production of a speech fragment of vocal interval duration by said first transmitter for connecting the output of said `first transmitter to said first channel and for transferring the output of `said fourth transmitter to said second channel, and means operated by energy caused by production of speech fragments of vocal interv-al duration by both said first and said second transmitters for transferment of *vocal interval duration by -said .addiring the output of said fourth transmitter to ,said third channel.

6. In a speech transmission system including `an east terminal and a west terminal, a first transmitter, a second transmitter and a third transmitter at said east terminal, corresponding first, second and third receivers at said West -terminal, a first speech transmission channel between said iirst transmitter and said first receiver, a second speech `transmission channel between said second transmitter and said second receiver and a third speech transmission channel between said third transmitter and said third receiver, a fourth transmitter at said east terminal, a fourth receiver at said `west terminal, means for connecting the output of Said fourth transmitter to said first channel, means operated by energy caused by production of a speech fragment of vocal interval duration by said first transmitter for connecting the output of said first transmitter to said first channel and for transferring the output of said fourth transmitter to said second channel, a distinctive frequency tone source at said east terminal, means operated by energy caused by production of a speech fragment ofivocal interv-al duration by said fourthl transmitter for connecting the output of said tone source to that channel to which the output of said fourth transmitter is connected and means controlled by said distinctive frequency tone for connecting said fourth receiver to the receiving end of the channel to which the output of said fourth transmitter is connected.

'7. In a speech transmission system including an east terminal and a west terminal, a first transmitter, a second transmitter and a lthird transmitter at said east terminal, corresponding first, second and third receivers at said west terminal, a first speech transmission channel between said first transmitter and said first receiver, a second speech transmission channel between said second transmitter and said second receiver, and a third speech transmission channel between said third transmitter and said third receiver, a fourth transmitter at said east terminal, a fourth receiver at said west terminal, means for connecting the output of said fourth transmitter to said rst channel if idle, and switching means operated by energy caused by production of a speech fragment of Vocal inter- `val duration by said first transmitter to transfer the output of said fourth ltransmitter to another of said channels.

8. In a speech transmission system including an east terminal and a West terminal, a .first transmitter, a second transmitter and a third transmitter at said east terminal, corresponding first, second and third receivers at said west terminal, a first speech transmission channel "between said first transmitter and said first receiver, a second speech transmission channel between said second transmitter and said second receiver, and a third speech transmission channel between said third transmitter and said third receiver, a fourth transmitter at said east terminal, a fourth receiver at said west terminal, means for connecting the output 'of said fourth transmitter to said first channel, switching means operated by energy caused by production of a speech fragment of vocal interval duration by any one of said first three transmitters to pi'event connection of the output of lsaid fourth transmitter to that channel which is between the speech producing transmitter and the corresponding receiver.

9. In a speech transmission system providing between stations a plurality of transmission paths over a like number of channels definitely assigned for use by said respective stations. the method of providing for an additional transmission path which comprises the step of switching the additional transmission path about among said channels at intervals when said channels are not being used for transmission by said stations.

10. In a speech transmission system providing between stations a plurality of transmission paths over a plurality of westward channels and a like number of eastward channels, said channels being definitely assigned for use by said respective stations, the method of providing for an additional transmission path in each direction which comprises the step of independently switching the additional westward path and the additional eastward path about among said respective westward channels and said respective eastward channels at intervals when said chanvnels are not being used for transmission by said

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