JPH0343839B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an audio system, and more particularly to a projection system and audio system that uses a compatible two-track release version, overcomes the problems of conventional multichannel systems, and provides three or more playback channels. Regarding system equipment.

It was not until the 1930 film ``Fantasia'' that prior art multi-channel movie sound systems used independent optical tracks for each channel to increase realism and dramatic or special effects. Later, with the introduction of widescreen processing such as CinemaScope and Cinerama, multiple magnetic soundtracks were used to provide six or more independent channels. In recent years, films such as ``Tommy'' and ``Pink Floyd'' have used multi-channel magnetic release versions, by placing two speakers in the back corner of the theater and two or three speakers in the front of the theater (left, center, right). Realized multi-directional audio.

In the past, multi-channel systems typically used independent soundtracks for each channel. Compatible stereo optical soundtracks have become popular in recent years, but most multichannel systems use more than two channels and generally magnetic tracks, adding extra cost to projection and audio equipment and making playback difficult. There are only a few theaters. Therefore, the standard optical version was also used in the majority of theatrical performances. In addition to the problem of the limited number of theaters equipped for magnetic first releases, the cost of manufacturing magnetic plates is significantly higher than that of optical plates, and therefore the number of useful plays of magnetic plates is even more limited. Theaters with multiple release equipment have generally opted for lower quality side channel speakers or rear (ambient) channel speakers to minimize cost rather than fidelity. Although recent improvements in magnetic multichannel have resulted in the use of two high quality rear channel speakers, this method also has drawbacks for several reasons. In other words, in terms of cost. The sound from the rear left or right becomes louder in each rear corner seat of the theater. Theaters are acoustically designed so that sound travels backwards from the screen (cushioned seat fronts, absorption by the audience), so point sources at the rear are reflected from the smooth, hard seat backs. may cause excessive direct repercussions. and that the large speaker box at the rear of the theater was aesthetically problematic.

To avoid the cost and compatibility problems of magnetic release plates, multi-track optical plates are contemplated. However, providing a motion picture film with more than two optical soundtracks has the following disadvantages, among others. Reproduction optics and pick-up cells become more complex and expensive. Deterioration of signal-to-noise ratio due to narrower tracks and increased total guard band area. Plate tolerance issues resulting from either narrow tracks or guard bands. A relative increase in boundary noise. A compatibility problem arises when all tracks are scanned at the same time and mono playback is performed. increased costs of electronic reproduction equipment; and the increased cost of optical recorders.

U.S. Patent Application No. Rohhart A. Berkovits and Kenneth J. Gundry, filed August 11, 1975.
No. 603,670, and U.S. Pat.
Two systems are disclosed that provide forward three-channel playback (left, center, right).

In the Berkovits et al. application, the L, C and R signals are encoded into a dual audio track.
That is, a portion of the C signal is added to the L and R signals, respectively. During playback, each track feeds an L or R speaker and a summing network, which drives the C speaker at a lower volume than the L and R speakers. Due to the delay feed circuitry to the R and L speakers, the center channel information appears to emanate from the C speaker, while stereophonic sound effects from the R and L speakers are maintained. Other L, C, and R reproduction systems for use with two-channel sources are disclosed in the Dolby et al. application. In the example,
Apparatus is provided for delaying the left and right channel playback signals relative to the center channel.
However, these applications are not directed to the unique problems of providing rear channel audio.

To overcome the problems in the prior art, the present invention is directed to a multi-channel movie audio system, in which the front stereo audio channel is compatible with at least one secondary audio channel or rear ambient audio channel in a dual bilateral soundtrack system. Alternatively, it may be encoded in a stereo variable area optical soundtrack format. Stereo variable area optical soundtrack systems are increasingly being used in industry and, because they offer complete compatibility, the first version of the present system can be used only in theaters with conventional mono optical projection and audio systems. not,
It can also be used in stereo reproduction equipment and theaters using the device according to the invention.

In the preferred embodiment, the right and left front (main) audio channels plus a single "environment" (secondary)
Set up an audio channel. Preferably, the environmental channel drives approximately three or more multiple environmental speakers located along the rear of the rear and side walls of the theater. In such an arrangement, the sound sources are integrated over a wide area, reducing proper reflection and allowing the volume of each speaker to be relatively low, so that the sound from one environmental speaker is so noticeable that people near that speaker may be disturbed. It does not affect other sound fields that you listen to. Improving sound localization by placing relatively directional ambient speakers above the side walls of the theater to counteract proximity effects in the direct sound field (often high frequencies) on the opposite side of the auditorium. You can also do it.

The present invention solves the significant problems encountered in encoding the environmental channel into the main audio channel. That is, in all non-independent multiplexed audio systems, crosstalk is included in the decoded signal due to the encoding process. Although it is acceptable for some information in the environmental channel to leak into the main channel, unnecessary forward channel crosstalk in the environmental channel is extremely undesirable due to the Haas effect or "priority effect." That is, two physically separated
When nearly identical sounds are emitted from two sound sources, whether one or both are heard and the apparent direction of the sound sources as perceived by the listener depend on the intensity of the sound in the listener's ears. Depends on the relative arrival time.

According to the Haas effect, if two sounds have the same intensity and arrive at the same time, the sound source will appear to be halfway between the two physical sound sources. If one sound source is delayed so that its arrival time is 5-35 milliseconds later than the other, the sound will appear to come only from the non-delayed source. That is, during this 5-35 millisecond "temporary concealment window" the first arriving sound masks the second sound. The concealment effect works even if the second arriving sound is about 10 dB louder than the first arriving sound.
If the arrival time difference is 35-50 milliseconds, the second sound source is perceived, but the sound source still feels like it is coming from the non-lag source. If the arrival time difference is large in a room with a short reverberation time, the listener will hear a sharp reverberation. If the second arriving sound is not of the same intensity but weak, the masking effect also works for arrival time differences of 35 milliseconds or more. The length of the temporary shielding window increases as the level of the second arriving sound decreases. For example, if the second arriving sound is 10 dB lower than the first arriving sound, few listeners will be disturbed by the second arriving echo sound even if the arrival time difference is more than 100 milliseconds.

If the listener is closer to the environment speaker than the main audio channel speaker, unwanted front channel crosstalk from the environment speaker will reach the listener in the theater before the same sound from the main audio channel.
In fact, in most cases when a listener hears crosstalk, they hear two separate sounds. That is, unnecessary crosstalk from the environmental channel speakers toward the rear of the audience seats, followed by the desired sound from the main channel. This is because the crosstalk sound reaches the listener's ears before the main channel sound and the intensity of the crosstalk sound is sufficiently lower than the main channel sound, so the same main channel sound is not masked by the crosstalk sound. .

The opposite condition, environmental crosstalk in the front channel, is less likely to be perceived. This is because the listener is close to the environmental speaker, so that the environmental sound from the environmental speaker reaches the listener before the crosstalk from the main channel speaker reaches the listener. It is also common practice to accommodate theaters that do not use environmental channel speakers by similarly mixing some environmental channel information into the front channels.

To overcome the problem of main channel crosstalk in the environmental channel speaker as described above, the present invention provides a delay time in the environmental channel reproduction device. Set the environmental channel delay times so that the relative arrival time difference is such that the sound from the main channel loudspeakers arrives at the listener's ears throughout most of the theater before any unwanted crosstalk from the environmental loudspeakers. do. As a result of providing such a delay time in the environmental channel, if a crosstalk component from the main channel sound is present in the environmental channel, the crosstalk sound component that is delayed in time due to the Haas effect is hidden by the main channel sound.

By providing an electrical delay in the environmental channel of approximately 75% of the time it takes for sound to propagate from the front to the rear of the theater auditorium, the sound from the main channel reaches almost all seats in the auditorium before the sound from the environmental channel. usually reached. When using the English system rather than the metric system,
It is easy to estimate this electrical delay by taking the speed of sound as approximately 1 foot/millisecond and expressing 75% of the length from the front to the back of the auditorium in feet. The electrical delay of such environmental channels is typically in the range of about 25-120 milliseconds. The 75% rule of thumb assumes a typical theater listening environment with the above-mentioned arrangement of environmental channel speakers.
In other words, in the theater concerned, directional environmental speakers are generally placed well above the listeners, so the direct sound from the environmental speakers jumps over the rearmost seats (approximately 10% of the rear of the theater) and is transmitted to the audience. Experience has shown that the front seats (an area approximately several meters in front of the approximately 10% area at the rear of the theater) are reached fastest, and as a result, the possibility of hearing crosstalk is greatest in seats located in front of the rearmost area. I understand. The present invention is intended to provide an arrival time difference of approximately 5-35 milliseconds for this range of seats by providing an electrical delay based on the 75% rule.

As mentioned above, by using the 75% rule to make the sound from the main audio channel reach almost all the audience seats before the sound from the environmental channel speakers, the desired main channel sound can be made to reach all the audience seats quickly. thus concealing unnecessary environmental channel crosstalk. Unwanted crosstalk is temporarily concealed, providing the strongest concealment effect (5-35 milliseconds) for the parts of the auditorium where crosstalk problems can be most severe (the part forward of the rear closest to the environmental loudspeakers). Reach within the window. For the rest of the auditorium, the high relative level of the main channel sound to the environmental channel crosstalk provides a concealment effect even with arrival times longer than 35 milliseconds. In this way the temporary concealment window becomes longer.

For home environments that are relatively small compared to the auditorium, the electrical delay time can be set so that nearly all seats in the room are within the temporary concealment window that provides the strongest concealment effect. An electrical delay on the order of 12-30 milliseconds will accommodate a typical chamber.

That is, to suppress the Haas effect, it is necessary to delay the crosstalk of the environmental channel by 5 to 35 milliseconds relative to the main speaker at the listener's ear position, and to achieve this, the listening room should be An electrical delay time equivalent to approximately 75% of the length from front to rear is given to the environmental channel. This 75% figure is empirical and assumes normal environmental speaker distribution and placement of the speakers well above the listener's head. It can be understood that when the listener's head is in direct contact with the environmental speaker, almost 100% of the delay time is required.

The quality of the environmental channel reproduction system is higher in the main channel, since the information carried in the environmental channel usually tends to be either steady-state background sound in nature or a reverberant signal that disguises spatial extent. There's no need. Therefore, the degradation of the environmental channel signal due to delay devices and low-quality speakers will not substantially affect the sound effect in actual use, while the main channel signal information is particularly important for realistic reproduction. They tend to contain overly important parts, such as the human voice, which require good fidelity. The present invention eliminates the viewer's perception of crosstalk in the rear channels and stabilizes the main channel signal, especially the highly transient content signal that is preferably perceived during playback by a high quality main channel playback system. This actually increases the fidelity of the main channel. Bass frequencies are not well separated by typical single band matrix encoding and decoding systems. Significant low temperature crosstalk therefore occurs between the main channel and the environmental channel. but,
The result is acceptable since bass frequencies are essentially omnidirectional and the effect is that the bass is perceived almost uniformly throughout the theater by the entire audience.

Preferred embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, the recording portion of the invention is illustrated in connection with a motion picture audio system. A device for encoding two or more audio signals into two channels, such as a conventional matrix encoder 2, receives two main audio channel signals, LF (front left) and RF (front right), into a pair of inputs. and receives processed sub-audio channel inputs at another pair of inputs, LB (left rear) and RB (right rear). The matrix encoder may be any of several four-channel encoders known to those skilled in the art, such as SQ or QS. LF and other symbols are commonly used in conjunction with such encoders in four-channel audio systems.

The inputs LF and RF of the matrix encoder 2 are received from the 3:2 logic circuit 3;
Independent signals of LF, C (center) and RF are applied. Logic circuit 3 may be of the type disclosed in the Berkovitz et al. application.

The circuit relates to conversion between a three-channel stereo audio system consisting of left, center, and right and a two-track soundtrack. This circuit delays the left and right channels by 3-35 milliseconds relative to the center channel based on the Haas effect in order to stabilize the localization of the center channel audio converted from the soundtrack. The purpose is to ensure that the sound can be heard stably from the center front in all audience seats. Therefore, this method only provides a fixed delay time within 3 to 35 milliseconds for sounds with a fixed level difference transmitted from the front to the rear, regardless of the theater size and seat position. This document does not provide any teaching regarding the present invention, which must take into consideration the position of the seat and the direction of propagation, as well as deal with each element of the propagation direction and level difference.

Main audio channel stereo signals LF and LF derived from independent multitrack masters (not shown)
The RF carries information rich in audio dialogue and other transient sounds to be reproduced by speakers placed behind or adjacent to the theater screen. The sub-channel input signal carries content, usually slowly varying low level background and reverberation information, to be reproduced by environmental speakers placed behind and to the rear of the theater seats. This is a so-called environmental signal.

Although independent sub-channel signals can be applied to the LB and RB inputs of the matrix encoder, it has been found that it is sufficient to use a single signal for environmental loudspeakers, so that the same signal can be applied to the two B applied to the input.

A secondary audio channel or ambient input signal is also derived from an independent multitrack master and processed before being applied to encoder 2. Since the effectiveness of the encoder 2 decreases with increasing frequency, the signal is applied to a low-pass filter 4 with an upper frequency limit, for example at about 7 kHz, to eliminate the high frequencies perceived from the environmental channel as a result of magimus adjustment angle errors. Reduce component crosstalk. Following filter 4,
A noise reduction encoder 6, preferably known to those skilled in the art as a Dolby B type encoder (matched with the decoder of the regeneration circuit), provides further processing of the signals LB and RB before being applied to the encoder inputs. The encoder is a Dolby B type complementary noise reduction device that is widely used in home tape recorders.The operating frequency band depends on the frequency and level of the dominant signal, and the gain changes only at intermediate levels. It is characterized by a bilinear characteristic that depends on the The same device is used in the environmental channel of the present invention to reduce noise due to hiss, electrical delays, crosstalk, etc. Noise reduction in the sub-channel or environmental channel is particularly desirable since random phase nozzles on the film tend to be more dominant in the reproduction of the environmental channel.

The outputs encoded by the encoder 2 on the two lines LT (left track) and RT (right track) are applied to a conventional soundtrack recording device. Although the invention primarily contemplates that the recording medium is a stereo-bilateral variable area optical soundtrack, the invention can also be used with other types of recording media having two tracks.

In the playback system of FIG. 2, a conventional soundtrack playback device 10 reads the encoded track and provides LT and RT signals to a matrix decoder 12. Decoder 12 is matched to encoder 2 and provides LF, RF, LB and RB outputs.
The LF and RF main channel outputs may be applied directly to the respective channels of a conventional electronic reproduction device and loudspeaker (not shown), or alternatively, as shown in the Type 2 in the Berkovitz et al. :3 logic circuit 14 which derives a center channel signal CF for application to playback electronics and speakers (not shown). A 2:3 logic circuit 14 may also be placed before the decoder 12. If desired, the aforementioned Dolby et al. or Berkovits et al. applications may be utilized with respect to LF, CF, and RF signals in recording and playback devices.

Combiner 16 receives and sums and applies decoder outputs LB and RB to low pass filter 18 .
Preferably, low pass filter 18 has an upper frequency limit at approximately the same frequency as filter 4 of FIG. The signal can be selectively applied to a high pass filter 20 having a lower frequency limit on the order of 80 hertz to prevent environmental speakers from clipping due to the high energy of the low frequencies which increases with decreasing frequency. A delay device 22 then delays the signal by approximately 75% of the path length from the front to the rear of the theater seating area in which the system is being used. In practice, a delay on the order of 25 to 120 milliseconds is desired, depending on the size of the audience seats. Such large delays are possible within the current state of the art with many different devices. The input to the decoder 24 is the encoder 6
A high-pass filter 20 may be placed after the decoder 24 to further complement the signal applied to the signal (FIG. 1). Such a filter 20 arrangement also tends to eliminate noise introduced by the delay device. A low pass filter 18 may also be placed after the decoder 24.

A noise reduction decoder matching encoder 6 of FIG. 1 follows the delay device. The output then drives an electronic playback device and environmental speakers.

In practice, standard environmental sound level 100% is set to -3 dB relative to 100% on film. The Dolby B encoder level is set at 50% on film.

In non-movie applications of the invention, the delay device is adjusted to suit the size of the room. In the case of a home four-channel audio system, the present invention can be adapted to a typical room with a fixed delay on the order of 12 to 30 milliseconds.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a recording section of a system implementing the present invention, and FIG. 2 is a block diagram of a reproducing section of a system implementing the present invention. 2...Matrix encoder, 3...3:2 logic circuit, 4
...Low pass filter, 6...Dolby B type encoder,
8... Soundtrack recording device, 10... Soundtrack playback device, 12... Matrix decoder, 1
4...2:3 logic circuit, 16...coupler, 18...
...Low pass filter, 20...High pass filter, 22...
...Delay device, 24...Dolby B type decoder, LF
...left front, C...center, RF...right front.

Claims (1)

Claims: 1. Receive first and second signals played from a two-track soundtrack, in which at least two main audio channel signals and at least one ambient audio channel signal are encoded; the at least two main audio channel signals and the at least one ambient audio channel signal for application to a main audio channel speaker and one or more ambient audio channel speakers located in front and behind the listening position, respectively; an audio matrix decoder that receives the first and second signals and decodes the first and second signals to derive the at least two main audio channel signals and the at least two main audio channel signals; said at least one comprising unwanted crosstalk from the signal;
a matrix decoder device for generating at least one ambient audio channel signal; and a device for receiving at least one ambient audio channel signal and processing the at least one ambient audio channel; a processing device for delaying the at least one ambient audio channel signal, providing a delay time such that the sound from the channel loudspeaker arrives before unwanted crosstalk of the same sound from the ambient loudspeaker; matrix decoder. 2. At a listening position in the room proximate to the ambient audio channel speakers, unwanted crosstalk from the main audio channel signal produced by the one or more ambient speakers is approximately 5. 2. A decoder as claimed in claim 1, in which the delay time of the time delay device is arranged to arrive after -35 milliseconds. 3. The decoder according to claim 1, wherein the delay time of the time delay device is set to about 75% of the sound propagation time from the front to the rear of the room. 4. The at least one ambient audio channel signal encoded on the two-track soundtrack is processed by a noise reduction encoder before being encoded onto the soundtrack, and the processing device comprises a noise reduction encoder. 2. The decoder of claim 1, further comprising a noise reduction decoder substantially complementary to . 5. The decoder of claim 1, wherein the processing unit includes a low pass filter for the at least one ambient audio channel. 6. The decoder according to claim 5, wherein the upper limit frequency of the low-pass filter is set at about 7 kilohertz.