WO1999040688A1 - Transmission de signaux audio de haute qualite sur les lignes telephoniques - Google Patents

Transmission de signaux audio de haute qualite sur les lignes telephoniques Download PDF

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Publication number
WO1999040688A1
WO1999040688A1 PCT/US1999/002468 US9902468W WO9940688A1 WO 1999040688 A1 WO1999040688 A1 WO 1999040688A1 US 9902468 W US9902468 W US 9902468W WO 9940688 A1 WO9940688 A1 WO 9940688A1
Authority
WO
WIPO (PCT)
Prior art keywords
standard
telephone line
modem
digital words
quality
Prior art date
Application number
PCT/US1999/002468
Other languages
English (en)
Inventor
Timothy G. Gilbert
Original Assignee
Gateway 2000, Inc.
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Gateway 2000, Inc. filed Critical Gateway 2000, Inc.
Priority to AU25849/99A priority Critical patent/AU2584999A/en
Publication of WO1999040688A1 publication Critical patent/WO1999040688A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M11/00—Telephonic communication systems specially adapted for combination with other electrical systems
    • H04M11/06—Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/66—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission for reducing bandwidth of signals; for improving efficiency of transmission
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B14/00—Transmission systems not characterised by the medium used for transmission
    • H04B14/02—Transmission systems not characterised by the medium used for transmission characterised by the use of pulse modulation
    • H04B14/04—Transmission systems not characterised by the medium used for transmission characterised by the use of pulse modulation using pulse code modulation
    • H04B14/046—Systems or methods for reducing noise or bandwidth

Definitions

  • the present invention relates to voice or other audio communication on a telephone system, and more specifically concerns increasing the apparent capacity of a standard telephone circuit for enhanced quality.
  • a standard voice-grade telephone line has, practically since the beginning of the twentieth century, provided less than the state of the art in voice-signal quality.
  • POTS plain old telephone service
  • the bandwidth and dynamic range for voice communications on a "POTS" (plain old telephone service) line has not improved to any significant degree. Indeed, we have become so inured to the characteristic low fidelity of voice transmission that few people consciously compare it to the much higher standards that they routinely expect from other audio media. And yet, the availability of higher-quality audio for ordinary telephone use is an unexpectedly pleasing experience to those who have experienced it. Although people condition themselves to expect low quality when using a telephone, they would appreciate a high-fidelity audio quality if it were available. For example, subtle nuances of language could be recovered. "Music on hold" service, as another example, would be more enjoyable at the quality level of a typical audio recording.
  • Dedicated telephone lines can provide voice communication at higher bandwidth and dynamic range. However, these lines connect only a small number of predesignated geographic locations together. They are permanently connected, billed by the month, and are quite expensive.
  • Multiple standard telephone lines can be coupled together to carry a single signal at a higher bandwidth; for example, filters may split a signal into an upper and a lower band, sending the lower part to one line, and the other through a frequency translator to another line; at the other end, another translator and a combiner reconstitute the original signal.
  • filters may split a signal into an upper and a lower band, sending the lower part to one line, and the other through a frequency translator to another line; at the other end, another translator and a combiner reconstitute the original signal.
  • Such special-purpose hardware is expensive and difficult to keep in proper adjustment; in addition, the extra standard telephone lines add extra ongoing cost.
  • Output s (Input)* ⁇ n( ⁇ +255* ⁇ Input ⁇ )/ln(256), where the input is normalized to 1.
  • Companding emphasizes the lower-volume signals, but sacrifices quality of larger signals. Users have become accustomed to this distortion. Companding was originally implemented to reduce perceived noise at the listener's end of the line, when the link between the central office and the customer was analog. Newer digital connections allow a better approach to be deployed.
  • the present invention improves the apparent capability of a standard- bandwidth telephone line to carry high-quality audio signals without requiring special, dedicated, or multiple telephone lines.
  • the invention employs equipment which is inexpensive and which is already available in many environments.
  • the quality of an audio signal is a measure of its usable frequency bandwidth and dynamic range, and improving the quality of an audio signal refers to increasing either or both of these parameters.
  • the invention samples and digitizes an audio signal at a rate and/or bit resolution corresponding to a frequency bandwidth and/or dynamic range higher than those of a normal telephone line, then transmits the resulting digital signal via a digital data modem over a standard-bandwidth, public switched-network telephone line.
  • a modem feeds the demodulated digital signal to a converter which transforms it back into a high-quality analog audio signal.
  • Fig. 1 is a block diagram of a preferred embodiment of the invention.
  • Fig. 2 is a flow chart of the operation of the embodiment of Fig. 1. Detailed Description of Preferred Embodiment
  • Fig. 1 is a block diagram of a system 100 according to the invention, set in an environment with which it may find the most common usage.
  • microphone 111 receives an audio voice signal from a user.
  • Any other input device such as a tape recorder (not shown) could also supply a high-quality analog signal.
  • Conventional analog-to-digital converter (ADC) 112 samples the input audio signal at a rate sufficiently high to preserve or enhance the signal's bandwidth on a standard voice telephone line.
  • a standard, voice-grade telephone line rolls off at about 4kHz.
  • the Nyquist rate the lowest rate for digitally representing an analog signal, requires a sample rate of at least 8,000 samples per second.
  • ADC 112 converts each sample to a stream of digital words.
  • the usable dynamic range of a standard telephone voice line is about 48dB, which requires at least eight bits in each sample.
  • CD-like quality usually considered the ultimate in audio-signal reproduction, employs 44,000 samples per second at a resolution of sixteen to eighteen bits in each sample, giving an upper frequency limit exceeding 20kHz and a dynamic range exceeding 90dB.
  • ADC 112 also divides the words into bytes, if necessary, to make the stream appear the same as though it had come from a computer or other standard source of digital data.
  • Modem 113 receives the digitized audio signal in the same way as it would receive a normal digital data signal.
  • Modem 113 may be a conventional 28.8kbps data modem commonly employed with a personal computer 114, and therefore already available in many settings in which the invention will be used.
  • Conventional modems compress the digital signal using any of a number of conventional protocols such as MNP-5 and V.42bis. They also add error- correction bits, most commonly in accordance with ITU standard V.42.
  • Modem 113 then modulates the digital words onto one or more carriers, using a conventional transmission format such as V.42bis (28.8Kbps).
  • Modem 113 may already be present at location 110, perhaps attached to a personal computer 114.
  • Public switched telephone network 120 carries the modem signal from line 121 to line 122 at a physically remote receiving location.
  • network 120 and lines 121-122 have a "POTS" bandwidth of about 3500Hz, at an analog dynamic range corresponding to about 48dB.
  • a data modem 133 compatible with modem 113 demodulates the signal from line 122, converts it from the transmission protocol to a digital word stream, checks and corrects errors, and decompresses the bits to their original form.
  • Digital-to-analog converter 135 transforms the bit stream to an analog audio signal, reassembling data bytes from the modem into words of the correct length, if necessary. Converter may also perform other conventional functions, such as amplification.
  • An audio output devices such as loudspeaker 136 converts the analog signal to audio form.
  • the output audio is a high-quality reproduction of the signal from input device 111.
  • Location 130 may include another personal computer 134, connected to modem 133 by a serial line.
  • An audio input device 131 and an analog-to-digital converter 132 allow a high-quality audio signal to be sent in the reverse direction over standard-bandwidth line 122.
  • a corresponding digital-to-analog converter 115 and audio output device 116 at location 110 complete the loop.
  • FIG. 2 is a flowchart of the transmission process 200. At the transmitting location 210, step 211 receives the analog signal, and step 212 samples it at a rate high enough to transmit a bandwidth greater than that of a standard telephone line, as described above.
  • block 213 low-pass filters the analog input signal.
  • Step 214 converts the samples to digital words having a sufficiently high dynamic range. E.g., 12 bit-words give a dynamic range of 4000:1, or about 30dB; 16 to 18 bits yields a CD range of about 90dB. Analog or digital preprocessing of the audio signal (not shown) may increase the effective dynamic range for a given word length.
  • Step 215 assembles the digital sample words into bytes; for example, two successive 12-bit words could be packaged as three 8-bit bytes.
  • Step 216 converts the digital word or byte stream to the format required for transmission. As mentioned previously, this step may be preceded or followed by techniques 217 used by conventional data modems for digital compression. Step 218 may add error-detection/correction codes. Step 219 modulates the formatted digital stream onto one or more carrier frequencies that fit within the bandwidth of the standard telephone line 121, Fig. 1. Step 220 transmits the modulated digital signal over a conventional switched public telephone network, or on any other type of low-bandwidth line, such as a carrier-current signal on an electrical power line.
  • step 231 demodulates the signal from line 122, Fig. 1.
  • Step 232 converts it from the line protocol to a digital bit stream. If step 217 had added error correction, step 233 then detects and/or corrects errors in the bit stream. Likewise, step 234 reverses any manipulation that step 216 may have introduced. Steps 232-234 may be performed in any sequence, as may steps 215-217 at the transmitting location.
  • Step 235 disassembles or unpacks the received bytes into a stream of digital words, if required.
  • Step 236 converts the digital words to a baseband analog signal, which is then converted to a sound output at step 237.
  • step 211- 237 again allows an audio signal to be communicated in both directions.
  • the steps of method 200 are performed substantially in real time. That is, except for signal delays and a small amount of incidental buffering in the modems or converters of system 100, the analog signal output at device 136 is contemporaneous with the analog input at device 111.
  • Table A below illustrates the compression ratios in step 217 required for various numbers of bits of resolution in analog-to-digital conversion step 214 at a constant sample rate of 8,000 samples per second in step 212.
  • the middle row shows raw speed, in kilobits per second, for the resolutions in the upper row.
  • Table A assumes a connect speed 28.8k bits per second for modems 113 and 133, Fig. 1. That is, Table A shows the improvement in dynamic range of an audio signal having a bandwidth equivalent to that of a standard-bandwidth POTS network.
  • Table B demonstrates compression ratios required for four of the resolutions in Table A, where the number of samples per second in step 212 is also increased, so as to improve bandwidth as well as dynamic range.
  • the' raw speed' quantity in Tables A and B is directly proportional to both sample size (resolution) and sample rate, it may be considered a measure of the quality of a digitized signal; because resolution and rate are respectively proportional to maximum dynamic range and bandwidth, this same quantity may also serve as one measure of the quality of an analog signal represented by the digital form, at least where the low- frequency cutoff point is not significant.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Telephonic Communication Services (AREA)

Abstract

L'invention concerne l'échantillonnage et la numérisation de signaux analogiques (111) au-delà du taux de Nyquist, pour une ligne téléphonique à largeur de bande classique du réseau téléphonique public commuté, aux fins de transmission via un modem sur une ligne (122) classique (113) à destination d'un site de réception (130). Les mots numériques du modem (133) correspondant sont reconvertis en échantillons analogiques à ce taux élevé. Les signaux analogiques considérés peuvent constituer des signaux audio de qualité élevée.
PCT/US1999/002468 1998-02-05 1999-02-05 Transmission de signaux audio de haute qualite sur les lignes telephoniques WO1999040688A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU25849/99A AU2584999A (en) 1998-02-05 1999-02-05 High-quality audio signals via telephone line

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US1886998A 1998-02-05 1998-02-05
US09/018,869 1998-02-05

Publications (1)

Publication Number Publication Date
WO1999040688A1 true WO1999040688A1 (fr) 1999-08-12

Family

ID=21790185

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1999/002468 WO1999040688A1 (fr) 1998-02-05 1999-02-05 Transmission de signaux audio de haute qualite sur les lignes telephoniques

Country Status (2)

Country Link
AU (1) AU2584999A (fr)
WO (1) WO1999040688A1 (fr)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993018607A1 (fr) * 1992-03-13 1993-09-16 Gec-Marconi Limited Perfectionnements apportes a la visiophonie
WO1996003837A1 (fr) * 1994-07-25 1996-02-08 Siemens Aktiengesellschaft Procede d'etablissement de liaisons et de commande de communications visiophoniques
WO1997002703A1 (fr) * 1995-07-06 1997-01-23 Diginet Systems Pty. Limited Technique de transmission a large bande virtuelle
US5602902A (en) * 1995-03-24 1997-02-11 Intel Corporation Four wire modem signal switching for voice and data applications
EP0781016A2 (fr) * 1995-12-18 1997-06-25 Sony Corporation Usages d'un appareil téléphonique pour un réseau d'ordinateur combiné avec un système téléphonique

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993018607A1 (fr) * 1992-03-13 1993-09-16 Gec-Marconi Limited Perfectionnements apportes a la visiophonie
WO1996003837A1 (fr) * 1994-07-25 1996-02-08 Siemens Aktiengesellschaft Procede d'etablissement de liaisons et de commande de communications visiophoniques
US5602902A (en) * 1995-03-24 1997-02-11 Intel Corporation Four wire modem signal switching for voice and data applications
WO1997002703A1 (fr) * 1995-07-06 1997-01-23 Diginet Systems Pty. Limited Technique de transmission a large bande virtuelle
EP0781016A2 (fr) * 1995-12-18 1997-06-25 Sony Corporation Usages d'un appareil téléphonique pour un réseau d'ordinateur combiné avec un système téléphonique

Also Published As

Publication number Publication date
AU2584999A (en) 1999-08-23

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