The current invention is a new and revolutionary system of distributing environmental sound and paging that uses as its propagation method the wiring that interconnects the PABX 1 to its telephone extensions.

The system is composed of two distinct parts called"Base"2 and"Station"3. The purpose of Base 2 is receiving audio (paging messages or environmental music), generating a carrier (which, as a non-limiting example, could be 455KHz), modulating this carrier (which as a non- limiting example could be frequency modulation (FM)), having as its modulation signal the received audio, and injecting the modulated signal into each pair of wires that interconnects the PABX 1 to each telephone 4 set. Base 2 can be located physically close to PABX 1; their interconnection can be easily understood from Figure I.

The purpose of Station 3 is receiving the modulated signal injected by Base 2, demodulating it, retrieving the audio signal, amplifying it and converting it again into sound through a loudspeaker. Station 3 can be located physically close to or distant from the telephone 4 set; it comprises two distinct parts: the Separator circuitry 15 and the Sound Retriever 28 circuitry. The connection of Station 3 with each telephone extension wiring as well as the overall system operation can be easily understood by examining Figure I.

Current"environmental sound and paging"systems use an extra pair of wires between the central sound unit and each sound box to be installe. These systems have a high installation cost since they require drilling mounting holes on the walls, either installation of extra and often-times extemal conducting tubes or installing the wiring into existing and clogged conducting tubes, besides lengthy installation time.

The Sound Line System (SLS) was conceived and developed to circumvent these hindrances. By taking advantage of the already existing wiring that interconnects the PABX 1 to the telephone extensions, the Sound Line System (SLS) provides a fast, cost effective and efficient installation, with no holes or work done on the walls. This invention (Sound Line System (SLS)) allows any existing telephone extension of the PABX 1 to receive environmental sound or paging, regardless of its state (on hold, on-the-hook, dialing, receiving dial tone, etc.).

The Sound Line System (SLS) also allows the volume of"environmental sound"and"paging" of each Station 3 to be independently adjusted. This means that a given user can adjust the environmental sound to his/her liking, and to adequate the volume of the paging messages as required by the environment, or yet not to listen to environmental sound and still listen to paging messages at proper volume.

The objectives and advantages of the Sound Line System (SLS) can be better understood while reading the following explanation in conjunction with the attached figures, which: Figure I represents the set Base 2 and Station 3 and shows how the Sound Line System (SLS) is used; Figure II depicts the block diagram of the Base 2 to better illustrate its functioning;

Figure III depicts the block diagram of the Station 3 for a better comprehension of its functioning.

As illustrated on Figure II, the Base 2 has an input"In sel"that selects which application will be used ("environmental sound"or"paging"). This feature is necessary to allow differentiated volume selection for"paging"and"environmental sound". Usually"environmental sound"is listened to in very low volume, whilst"paging"requires a louder volume to prevent the listeners from misinterpreting the messages. When the ln selsHnput (a digital input that can be TTL as a non- restrictive example) is at"level 0", it turns the Analog Key 6 to position 1 (as shown on Figure II, thus routing the signal from input"In VA"-which is the"paging"signal to input"In 1"of Adder 2,7.

"Level 0"at"In sel"input of Base 2, also places a sine wave signal (which can be a 5 Hz sine wave as a non-limiting example) at the"Out"output of the Tone Generator 13. This 5 Hz signal is then added to the voice signal coming from the Analog Key 6 within Adder 2,7. The resulting signal (consisting of"paging"plus 5 Hz tone) is sent to the input of the Amplifier 1,8.

When"level 1 n is present at the"In sel"input, the Analog Key 6 is turned to position 2. This routes the"environmental sound"signal-that comes from the"In SA"input-to the input of Adder 2,7."Level 1"at the"In sel"input also prevents any signal from exiting the"Out"output of the Tone Generator 13. As a consequence, Adder 2,7 delivers only the"environmental sound"signal (without the 5 Hz tone) to the input of Amplifier 1,8.

As illustrated on Figure II, the"In SA"input accepts both monophonic and stereophonic equipment. If the sound generator equipment is a stereophonic one, Adder 1,5 will add the two channes ("L"and"R"), transforming them into a monophonic signal before it is delivered to the Analog Key 6. If the sound generator equipment is a monophonic one, it is sufficient to connect it to either"L"or"R"input of"In SA" (one of them can be left open). Adder 1,5 will then deliver the monophonic signal to the Analog Key 6.

The conclusion is that two types of signal can be presented to the input of Amplifier 1,8: paging"plus 5 Hz tone when °In sel"is at"level 0", or"environmental sound"signal when"In sel"is at"level 1".

Amplifier 1,8 amplifies the signal at its input to an adequate value that can modulate the carrier generated by the Modulator Oscillator 11. Figure II illustrates that between Amplifier 1,8 and Modulator Oscillator 11 there is a circuit called Pre-emphasis 9. The function of Pre-emphasis 9 is to provide a variable attenuation according to the input-signal frequency, in such a way that higher frequency components undergo a lesser attenuation than the lower frequency components (this technique is commonly used in frequency modulation circuitry, and therefore requires no further explanation on this document).

The output of Pre-emphasis 9 goes to the Level Detector 10 circuit. Level Detector 10 warns the user whether the audio inputs"In SA"and"In VA"are exceeding or not the desired levels.

When the level is exceeded, an LED (light emitting diode) of the Level Detector 10 lights up indicating the user should turn down the volume of the audio signal (either"paging"or "environmental sound") that is injected at the input of Base 2. For proper functioning of the"Sound Line System (SLS)", the user should adjust the level of uIn AS"or"In VA"inputs to the highest

possible level that yet does not turns on the LED. If the user exceeds the input level (lit up LED), the signal recovered by Station 3-whether"environmental sound"or"paging"-will suffer distortion. If the user adjusts to an excessive low level, the signal-to-noise relationship of the signals recovered by Station 3-"environmental sound"and"paging"-may not be good.

As illustrated on Figure II, the"in mod"input of the Modulator Oscillator 11 receives the "environmental sound"or"paging"plus 5 Hz signal at such adequate levels that a carrier can be modulated, as a non-limiting example, to a 455 kHz frequency. The modulated carrier can then be amplifie by Amplifier 2,12 and sent to the Extension Amplifiers 14. The Extension Amplifiers 14 have a high impedance input and can be installed in parallel without causing level loss to the carrier.

There is a Separator Circuit 15 formed by T1, D1, D2, C2, C3, L1 and L2 at the output of each Extension Amplifier. The modulated carrier is transformed by T1 into a balanced carrier, which propagates better on pair of wires (and this is the case of telephone extensions). The balanced carrier reaches then capacitors C2 and C3, which present low impedance at 455KHz and thus transfer the balanced carrier to the pair of wires (the telephone extension) connected at the "Out LR"output of Base 2 (see Figure II). Inductors L1 and L2 present high impedance at 455 kHz whilst capacitor C1 has low impedance at this same frequency, forming all three an effective let- pass-low-frequency filter that prevents the carrier to exit the"In PABX"access connected to the PABX 1. At the maximum frequency (3200 Hz) used on telephone signals (audio, access tone, dialing pulses, ringing pulses, DC levels, etc.) between the PABX 1 and the extension telephone sets 4 capacitors C2 and C3 present high impedance and transformer T1 present low impedance, forming all three a let-pass-high-frequency filter preventing these signals from getting into the Base 2 circuitry and from disturbing its proper functioning. Because C2 and C3 have high impedance at 3200 Hz they prevent Base 2 from excessively loading the PABX 1 access and from affecting its proper functioning.

Inductors L1 and L2 present low impedance at 3200 Hz, whilst capacitor C1 presents high impedance at this frequency, and together allow the signals coming from the PABX 1 and from the telephone extension 4 circulate between the"Out LR"and"in PABX"accesses of Base 2 without any loss.

Diodes D1 and D2 protect the Base 2 against tension surges inducted on the wiring of the extension-they short circuit above a specified voltage level.

The conclusion is that the Separator Circuit 15 is the circuitry that allows both the telephone 4 signals and the modulated carrier to share the same wiring (of the telephone extension) without any interference (and signal loss) between them.

As illustrated on Figure II, there is also on Base 2 a Power Supply 16 to convert the AC power source to a DC signal denominated Vcc, that feeds all circuits of the Base 2.

After the Base 2 injects the modulated carrier with audio into the line of each telephone extension, a Station 3, comprising a Sound Retriever 28 circuit and a Separator Circuit 15 is needed on the other end of each extension line to retrieve this signal and convert it into "environmental sound"or"paging".

The electrical diagram of the Station 3 is on Figure lil. The aln LR"input should be connected where the telephone 4 set was, and the telephone 4 set should then be connected to the"Out Tel" output. This is how the modulated carrier coming from the Base 2 enters the"In LR"input of the Station 3 via the wiring of the telephone extension.

The carrier comes to transformer T1 through capacitors C2 and C3 (on Separator Circuit 15) that present low impedance to the carrier frequency (455 kHz). T1 transforms the carrier to a balanced carrier and delivers it to"RPF" (range-pass filter). Inductors L1 and L2 present high impedance at 455 kHz and capacitor C1 present low impedance at this frequency, forming thus a let-pass-low-frequency filter that prevents the carrier from entering the Telephone 4 circuit and from causing its improper functioning. Capacitors C3 and C3 present high impedance at the frequencies (maximum of 3200 Hz) of the telephone 4 signals, while transformer T1 presents low impedance at these frequencies; C2. C3 and T1 prevent the telephone 4 signals from entering the Station 3 circuitry and its improper functioning, and also force Station 3 to present high impedance to the telephone 4 signals.

The telephone 4 signals that circulate back and forth between the PABX 1 and the telephone 4 set, barred from entering Station 3, flow to"In LR"and"Out Tel"accesses through inductors L1 and L2 that present low impedance to these frequencies, thus causing no side effects on the quality of the communication between the PABX 1 and the telephone 4 extension. Capacitor C1, that presents high impedance to the frequencies of the telephone 4 signals causes no side effects to them either.

Diodes D1 and D2 protect the Base 2 against tension surges inducted on the wiring of the extension because they short circuit above a specified voltage level.

The conclusion is that the Separator Circuit 15 of the Station 3 as well as the Separator Circuit 15 of the Base 2 are also the circuitry that allow both the telephone signals 4 and the modulated carrier to share the same wiring (of the telephone extension) without any interference (and signal loss) between them.

Figure III shows the output of the Separator Circuit 15 connected to the input of"RPF" (range-pass filter), that serves the purpose of limiting the band of the carrier to 30 kHz (as a non- limiting example) around the 455 kHz frequency (also supplied as non-limiting example). This filter also has the function of rejecting unwanted electromagnetic noises coming from electric motors and switches, FM and AM signals, etc. Figure III also illustrates that the signal exiting the"RPF"17 gets into Demodulator 18, which demodulates the carrier, that is, recovers the audio signal to either ;'environmental sound"or"paging"plus 5 Hz tone (according to the selection on Base 2). The demodulated signal is then sent to the De-emphasis 19 circuit that presents less attenuation at lower frequencies to compensate the effect caused by the Pre-emphasis 9 circuit of the Base 2. No in-depth explanation is provided on this document about the Pre-emphasis 9 and De-emphasis 19 circuits, because these are commonly-used circuits on FM transmitters and receivers.

The audio signal exiting De-emphasis 19 gets to potentiometers Pot 1,26, Pot 2,27 and to Tone Detector 21 (see Figure lit). When Tone Detector 21 receives the"environmental sound" signal at its"In"input. its"Out"output stays at"level 0", keeping the Analog Key 22 at position 2.

This way the"environmental sound"signal exiting the De-emphasis 19 circuit gets to the input of the Audio Amplifier 23 through Pot 2,27. It is through Pot 2,27 that the level of"environmental sound"at the input of the Audio Amp 23 user can be adjusted. Taking into account that the Loudspeaker 24 is connected to the output of the Audio Amp 23, the user can control the volume of the environmental sound through an external button of Pot 2,27, as illustrated on Figure))).

When"paging"plus 5 Hz tone gets to the"In"input of the Tone Detector 21, the detection of the 5 Hz forces its"Out"output to"level 1"turning the Analog Key 22 to position 1. This way the "paging"plus 5 Hz signal exiting the De-emphasis 19 circuit gets to the input of the Audio Amplifier 23 through Pot 1,26 and the LPHF 20 (let-pass-high-frequency filter). LPHF 20, which cuts frequencies lower than 300 Hz, filters the 5 Hz, and only the"paging"signal gets to the input of the Audio Amplifier. The level of the"paging"signal can be adjusted through potentiometer Pot 1,26 reaching the Audio Amplifier 23, that is, the volume of"paging"can be adjusted through Pot 1,26 because the Loudspeaker 24 is connected to the output of the Audio Amp 23. Pot 1,26 does not have an external button (this is a non-limiting example); it can be adjusted with a special tool through a small hole on the cabinet of the Sound Retriever 28. This is to prevent non-authorized personnel to improperly adjusting the volume of"paging".

Figure III shows a Power Supply 25 in the Station 3. It converts the AC signal from the external power source to a DC signal called Vcc. Vcc feeds all electrical circuitry of Station 3 Summing up the above description, as illustrated on Figure I11, Station 3 comprises the Separator Circuit 15 and the Sound Retriever 28. There are no technical reasons, however, that prevent the Separator Circuit 15 within the same cabinet containing the Sound Retriever 28.