EP0630168B1 - Improved Dolby prologic decoder - Google Patents

Improved Dolby prologic decoder Download PDF

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Publication number
EP0630168B1
EP0630168B1 EP19940108673 EP94108673A EP0630168B1 EP 0630168 B1 EP0630168 B1 EP 0630168B1 EP 19940108673 EP19940108673 EP 19940108673 EP 94108673 A EP94108673 A EP 94108673A EP 0630168 B1 EP0630168 B1 EP 0630168B1
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EP
European Patent Office
Prior art keywords
signal
decoder
block
surround
dolby
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.)
Expired - Lifetime
Application number
EP19940108673
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German (de)
English (en)
French (fr)
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EP0630168A1 (en
Inventor
Aki Dr. Mäkivirta
Raimo Jokinen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nokia Technology GmbH
Original Assignee
Nokia Technology GmbH
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Filing date
Publication date
Application filed by Nokia Technology GmbH filed Critical Nokia Technology GmbH
Publication of EP0630168A1 publication Critical patent/EP0630168A1/en
Application granted granted Critical
Publication of EP0630168B1 publication Critical patent/EP0630168B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S3/00—Systems employing more than two channels, e.g. quadraphonic
    • H04S3/02—Systems employing more than two channels, e.g. quadraphonic of the matrix type, i.e. in which input signals are combined algebraically, e.g. after having been phase shifted with respect to each other

Definitions

  • the Dolby Surround Sound system is widely used as the sound system of movies but also in video cassettes and other video recordings.
  • the system is also extending to television applications with stereo sound.
  • the system has four sound channels: left (L), right (R), center (C) and surround (S). They are encoded in a Dolby encoder so that L and R are transmitted in the normal way, but the C and S channels are phase encoded and included in the L and R channels.
  • Both the center channel C and the surround channel S are divided equally into the L and R channels, but the components of the surround channel S added to the left and right channels have a phase difference of 90 degrees.
  • the decoder again separates the encoded four channels.
  • the left channel L and the right channel R are supplied as such to the decoder output.
  • These channels also contain information of the channels C and S.
  • the center channel is detected as the sum of the the L and R channels (the surround information with opposite phases is canceled) and the S channel is detected as their difference (the center channel information with the same phase is canceled).
  • the L and R sounds are localized in a normal way.
  • the center channel C is localized in the middle of the stereo pair, and the surround channel S is not clearly localized anywhere, but is heard from an indefinite direction.
  • the encoder is quite simple to realize, and it comprises mainly a simple differential amplifier, a delay means and filters.
  • the disadvantage of the encoder is that even if the difference between the main channels L and R as well as the difference between the center channel C and the surround channel S is higher than 40 dB, the difference between the adjacent channels (e.g. S and L) is only 3 dB. Therefore we have a quite small area in which the stereo pattern is good, and in which the center channel sound seems to be emitted from the middle. Also there is not a good isolation between the front and back areas, because the surround loudspeakers placed behind or on the sides of the listening space will reproduce also the difference information between the left channel L and the right channel. Therefore passive decoders cannot locate the sounds very accurately, in other words, the sound is not received from a correct, defined direction, but there is an indefinite impression of the sound.
  • An active decoder could be conceived as a passive decoder having a processing circuit connected to it.
  • the active decoder is called Dolby Prologic. This process examines the balance on the axes L-R and C-S. The Prologic processing tries to keep the total power at a constant level. A dominating sound is enhanced by attenuating the other channels. Thus it is possible to substantially increase the apparent channel difference.
  • Figure 1 shows a block diagram of the known Dolby Prologic decoder.
  • the decoder inputs are the left channel Lt and the right channel Rt, containing the encoded center channel C and the surround channel S.
  • the level difference of the input signals is corrected in blocks 1 and 2.
  • the adaptive matrix block 6 of the Prologic circuit generates all channels L, R, C and S.
  • the surround channel S is supplied to the filter 7 preventing enfolding, and through the delay means 8 adjusted by means 9, and through the low-pass filter 10 to a modified B-type Dolby noise attenuator 11.
  • the modified Dolby B noise attenuator is developed by Dolby, and it differs from a conventional in that its noise attenuation is only half of that in the conventional attenuator.
  • the surround signal S obtained from the attenuator output is then supplied to the output level controller 12, which also receives the signals of the left L, the right R and the center channels generated by the adaptive matrix block 6 of the Prologic circuit.
  • the output level controller At the output of the level controller we obtain all four channels as encoder output signals.
  • the noise sequencer 3 can adjust the correct levels of the different channels.
  • the adaptive matrix block 6 is the nucleus of the decoder, and at the same time the fact distinguishing it from a passive decoder.
  • the block comprises two main sections: the adaptive logic, and a matrix comprising voltage controlled amplifiers VCA which improve the channel separation.
  • the adaptive block continuously monitors the Rt and Lt sound channels at its input and from these it in a known way calculates sums and differences of the sound channels utilizing the signal level ratios of the R and L channels and C and S channels. So it examines in which direction the momentary dominance of the sound field is located. To determine this each main signal (L, R, C, S) is first full-wave rectified, the obtained DC voltages are logarithmically transformed in pairs, and then their differences are formed.
  • control signals are further processed in the adaptation section of block 6 so that a set of control voltages (16 voltages) are obtained and supplied to the amplifier section of block 6, the amplifier section thus comprising a matrix of several voltage controlled amplifiers (VCA).
  • VCA voltage controlled amplifiers
  • the VCA matrix also receives as input signals the received signals left Lt and Rt. Control voltages control the amplification of the VCA amplifier, and then the matrix produces as outputs the signals R, L, C and S containing the direction information, which is amplified in the dominance direction and proportional to them as calculated by the adaptation block. Then, in the same way as in a passive Dolby decoder, the L, R and C signals are supplied to the main level controller 12 which also receives S through the side branch, as shown in figure 1.
  • this known Dolby Prologic decoder has some disadvantages, particularly in television applications. More and more television receivers are provided with Dolby Surround Sound decoders. As said above, after the encoder there are four audio channels, L R, C and S, which are available for any further processing of the audio signal arranged by the television manufacturer. Thus the further processing must be made separately for each audio channel, which leads to very expensive practical realizations.
  • the object of the invention is to create an arrangement to minimize the effort of the further processing.
  • the surround channel is processed by Dolby B decoding, as illustrated in figure 1.
  • This is a non-linear operation producing an effect which changes as the signal value changes.
  • the signal processing block of the invention changes the value of the surround signal, it can not be supplied to the Dolby B decoder. Therefore, in the application according to the proposed solution, the level of the surround signal is detected before the linear DSP block, and this information is used to control the Dolby B process, whereby the linear operations in block DSP do not anymore have an adverse effect on the operation of the Dolby B block.
  • FIG 1 shows the adaptation and VCA amplifier matrix block 6 of figure 1, to which a linear signal processing block 23 of the invention is added.
  • the input signals to the prior art block 6 are the sound channel signals right Rt and Lt, into which the center channel C and the surround S channel are encoded (figure 2).
  • the encoded input signals would be connected both to the Dolby Prologic adaptation block, which determines the direction having the momentary dominating signal, and to the amplifier block, which comprises a matrix of voltage controlled amplifiers VCA.
  • the adaptation block forms control signals controlling the gain of each VCA amplifier. At the output of the matrix we obtain four audio channels R, L, C and S.
  • the block 23 contains at least one digital signal processor DSP.
  • the DSP block 23 can perform desired operations, such as filtering, equalization and so on.
  • the desired operations can be selected for each application and can be freely determined by the television manufacturer. Because there are only two channels to be processed we need only two filters and not four, as the case would be, if the audio signals would be processed after the Dolby encoder.
  • the processed signals of the left and right channels are connected from the DSP block to the VCA amplifier block 22, which then in a known way generates the four audio channels.
  • the surround signal obtained from the amplifier block 22 can not be supplied to a non-linear Dolby B decoder, because the DSP block 22 has changed the value of the surround signal. Therefore the input signals are connected also to the surround signal level detector 24.
  • the detected surround signal is now a surround "correctly" encoded into the input signals, so that this signal is connected to the Dolby B decoder. This decoder now operates properly.
  • the invention has several advantages compared to audio signal processing after the decoder. First of all there are only two channels (Lt, Rt) to be processed, and still this has an effect on all four output channels of the decoder. In the second place there is a smaller need for equipment when the processing is made in hardware, or less signal processor code is required when the arrangement is realized in software. In the third place the processing of two channels does not require as much processing power as the processing of four channels.
  • the linear processing made according to the invention does not interfere with the function of the Dolby decoder itself.
EP19940108673 1993-06-15 1994-06-07 Improved Dolby prologic decoder Expired - Lifetime EP0630168B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI932735 1993-06-15
FI932735A FI102799B (fi) 1993-06-15 1993-06-15 Paranettu Dolby Prologic -dekooderi

Publications (2)

Publication Number Publication Date
EP0630168A1 EP0630168A1 (en) 1994-12-21
EP0630168B1 true EP0630168B1 (en) 2001-04-04

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP19940108673 Expired - Lifetime EP0630168B1 (en) 1993-06-15 1994-06-07 Improved Dolby prologic decoder

Country Status (3)

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EP (1) EP0630168B1 (fi)
DE (1) DE69427001T2 (fi)
FI (1) FI102799B (fi)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TW247390B (en) * 1994-04-29 1995-05-11 Audio Products Int Corp Apparatus and method for adjusting levels between channels of a sound system
EP0808076B1 (de) * 1996-05-17 2007-11-21 Micronas GmbH Raumklangsystem
SE521465C2 (sv) 1999-06-07 2003-11-04 Ericsson Telefon Ab L M Mobiltelefon med taligenkänningssystem innehållande en beräkningsenhet för spektralavstånd.
US7003467B1 (en) * 2000-10-06 2006-02-21 Digital Theater Systems, Inc. Method of decoding two-channel matrix encoded audio to reconstruct multichannel audio
TWI420918B (zh) * 2005-12-02 2013-12-21 Dolby Lab Licensing Corp 低複雜度音訊矩陣解碼器

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4589129A (en) * 1984-02-21 1986-05-13 Kintek, Inc. Signal decoding system
US4799260A (en) * 1985-03-07 1989-01-17 Dolby Laboratories Licensing Corporation Variable matrix decoder
JP3108087B2 (ja) * 1990-10-29 2000-11-13 パイオニア株式会社 音場補正装置

Also Published As

Publication number Publication date
FI932735A0 (fi) 1993-06-15
FI102799B1 (fi) 1999-02-15
EP0630168A1 (en) 1994-12-21
DE69427001T2 (de) 2001-09-06
FI932735A (fi) 1994-12-16
FI102799B (fi) 1999-02-15
DE69427001D1 (de) 2001-05-10

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