Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04S—STEREOPHONIC SYSTEMS 
  • H04S1/00—Two-channel systems
  • H04S1/002—Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution

Definitions

• the present invention relates to a sound pro ⁇ ducing system particularly adapted to create a dimen ⁇ sionalized impression of the sound and to produce a recording capable of creating the dimensionalized impression of the sound.
• a "diraension- * alized" effect can be obtained by transmitting differ ⁇ ent sound signals to the two speakers.
• the speakers being positioned at two laterally spaced locations, and the listener being positioned rear- wardly of the speakers and facing toward a location between the speakers, a distinct sound that is trans ⁇ mitted only from the left speaker can be detected by the listener as coming from that source since the left and right ears of the. listener will detect a difference in intensity and also detect a phase shift so as to obtain the impression of the direction of the sound.
• the direction of that source of sound can also be detected by the listener .
• the sound can be expanded to the area encompassed by the two speakers .
• the apparatus of the present invention is provi ⁇ ded to produce a dimensionalized audio signal to be used in conjunction with a pair of speakers where there is a playing area, where there are right and left speakers positioned at right and left speaker locations , and there is a listening area with a lis ⁇ tening location- At the listening area there are right " and left ear locations corresponding to right and left ear positions of a person's head which could be located at said listening locations and facing toward the playing area.
• the apparatus comprises a left input means to receive a left stereo signal and a right input means to receive a right stereo signal.
• left main transmitting means to trans ⁇ mit a left main signal component, corresponding and similar to the left stereo signal, to the left signal output means.
• right main transmitting means to transmit a right main signal component, corresponding to and similar to the right stereo signal, to the right signal output means.
• a left to right compensating means adapted to receive the left stereo signal to produce an inverted and delayed left to right compensating signal, corresponding to the left stereo signal, and to transmit said left to right compensating signal to the right signal output means.
• right to left compensating means adapted to receive the right stereo signal to produce an in ⁇ verted and delayed right to left compensating signal corresponding to the right stereo signal, and to transmit the right to left compensating signal to the right signal output means.
• the two compensating signals are delayed relative to corresponding main signal components by a time delay period within a . predetermined time delay range.
• the left signal output means produces a left audio signal comprising the left main signal component and the right to left compensating signal.
• the right signal output means produces a right audio signal comprising said right main signal component and said left to right compensating signal.
• the result is that when the left audio signal drives the left speaker and the right audio signal drives the right speaker, the following occurs: a. there is a left audio output having a main left sound component and a right to left com ⁇ pensating sound component, said left audio output having a primary path component from . said left speaker to said left ear location, and a secondary path component from said left speaker to -said right ear location, b.
• a right audio output having a main right sound component and a left to right compensating component, said right audio out ⁇ put having a primary path component from said right speaker to said right ear location, and a secondary pa * ch component from said right speaker location to said left ear location, c. the main left sound component reaches the left ear without being cancelled to a sub ⁇ stantial amount, d. the right main sound component reaches the right ear location without being cancelled to a substantial amount, e. the main left sound component travelling its secondary path to said right ear location is cancelled to a substantial amount by the left to right compensating sound component * travelling on the primary path from said right speaker to said right ear location, f.
• time delay distance which is that distance that sound travels during the corresponding time delay period.
• the apparatus is further characterized in that the time delay range for the compensating signals has a smaller time delay limit with a corresponding smaller time delay limit distance, and a larger time delay j-.lmi-c having a corresponding larger time delay distance limit.
• the smaller and larger time delay distances encompass a range which includes an optimum time delay distance equal to a value obtained by mul- tiplying the sine of either listening angle times the ear spacing distance . .
• each of the compensating signals have a plurality of compensating signal components, each having a different corresponding time delay distance component. Desirably at least one of these time delay distance components is smaller than the optimum time delay distance. Also, desirably at least one other of the time delay distance components is greater than the. optimum time delay distance.
• At least some of the com ⁇ pensating signal components have decibel values lower than a decibel value of the corresponding main sound component.
• at least one of the compensating signal components has a decibel value which varies with frequency, with lower frequencies of that com ⁇ pensating signal component having a higher decibel value than at higher frequencies of that compensating signal component .
• the left and right main transmitting means com ⁇ prises, in the preferred form, frequency equalizer means.
• Each of the frequency equalizers produces its main signal component with a higher decibel level for lower frequencies and a lower decibel level for higher frequencies .
• This apparatus can also be used to produce re ⁇ cordings which can in turn produce dimensionalized sound.
• a stereo re ⁇ cording device operatively connected to the left and right signal output means to receive the left and right audio signals.
• the stereo recording device pro ⁇ Jerusalem a stereo sound recording with right and left information channels corresponding to the left and right audio signals.
• the left signal output means produces the left information channel which comprises the left main signal component and said right to left com ⁇ pensating signal.
• the right signal output means pro ⁇ Jerusalem the right * information channel which comprises the right main. signal component and the left to right compensating signal .
• the left information channel drives the left speaker
• the right information channel drives the right speaker .
• left and right stereo signals are directed into left and right input means, respectively.
• a left main signal component corresponding and similar to the left stereo signal, is transmitted to a left signal output means.
• a right main signal component, corresponding to and similar to the right stereo signal is trans ⁇ mitted to a right signal output means.
• the signal output means is used to produce sound through speaker means .
• the signal output means are used to produce a sound recording which in turn can produce the desired sound components when played through a conventional stereo system.
• the effect of the present invention is to produce a highly dimensionalized sound with a relatively high tolerance to head position and angle of the listener.
• Other features will become apparent from the follow ⁇ ing detailed description.
• Figure 1 is a schematic view illustrating the manner in which high quality stereo recordings are made
• Figure 2 is a schematic view showing the manner in which a person receives sound waves-from the spea ⁇ kers of a typical audio system
• Figure 3 is a schematic illustration of the appa ⁇ ratus of the present invention producing sound for a listener
• FIG 4- is a schematic diagram of a switch in the apparatus of Figure 3;
• Figure 5 is a table illustrating the magnitude of the compensating signal output components of the compensating signal
• Figure 5 is a graph illustrating the intensity of the main signal component, as a function of fre ⁇ quency, produced by each of the frequency equalizers producing the main signal component;
• Figure 7 is a schematic showing, similar to Figure.1 , to illustrate operating features of the present invention.
• Figure.8 is a view of the listening area of Figure 5 to illustrate other operating features of the present invention.
• Figure 9 is a view similar to Figure 8 , showing further operating features of the invention.
• Figure 10 is a schematic illustration of the present invention producing signals for a stereo recorder. Best Mode For Carrying Out the Invention
• FIG. 1 there are shown two microphones Ml and M2 spaced from each other and positioned in * front of an orchestra, indicated generally at 10, and comprising a plurality of orchestral components
• micro ⁇ phone Ml may pick up the sound in the order of appro ⁇ ximately 1/100 of a second later than the microphone M2, since the sound must travel further to the micro ⁇ phone Ml .
• the sound emanating from the instrument 12b would reach the .microphone Ml sooner and at a higher intensity than the sound from the instrument 12b would reach the microphone M2.
• the microphone M2 At some intermediate location, e.g. at the location of the
• the sound would reach the two micro ⁇ phones Ml and M2 at approximately the same time and same intensity.
• the sound transmitted to the micro ⁇ phone Ml is used to produce a first signal which in turn is transmitted to the stereo recorder and repro ⁇ symbolized in the recording in a manner that when the re ⁇ cording is played, this signal, corresponding to the sound at microphone Ml , reproduces in One of the speakers a sound which is a substantial reproduction of the sound reaching the microphone Ml .
• the sound reaching the microphone M2 is recorded in a manner that when the recording is played, the signal driving the other speaker corresponds to the sound transmitted to the microphone M2.
• the speaker LS will first repro ⁇ duck this sound at the higher intensity level .
• this sound would 'have first -and second components Ll and Lr reaching the left and right ears, Le and Re, respectively.
• the two ears Le and Re would detect a difference in intensity of the two sound components Ll and Lr and also a phase shift of possibly 100 to * 300 microse ⁇ conds so that there would be a very definite sense of direction from the left speaker Ls .
• the secondary sound component Lr is somehow eliminated so that in that first instant, only the left ear Le hears the sound which is travelling along the major sound com ⁇ ponent path Ll.
• the instantaneous impression created on the person P is that the sound has emanated from a location which is more nearly immediately to the left of the person P.
• the immediate impression is that the sound is totally out of the speaker area and is somewhere near the left side of the person.
• the reproduction of these sounds in the two spea ⁇ kers LS and RS is timed somewhat closer together so that the left ear and the right ear Le and Re hear these two closer to the same intensity and somewhat closer together in a time frame.
• the dimension ⁇ alized effect with regard to the sounds corresponding to those emanating from the instruments 12e and 12c can be presumed to be somewhat less than in the case of sounds emanating from the instruments 12b and 12f.
• the overall effect of this is a rather startling creation of the impression that the sound is "totally dimensionalized” , in that the_ hearer somehow appears to be "within the sound" or in some manner surrounded by the various sources of the sound.
• the appa ⁇ ratus can be so arranged that it isnot overly sensi ⁇ tive to the position or angle of the listener's head. For example, let it be assumed that the hearer is attracted more to a sound which appears to be coming in the direction from the left and the hearer turns his head toward that speaker. The dimensionalized effect created by the present invention is not sub ⁇ stantially diminished. Further, the hearer is able
• Each of these frequency equalizers A(L) or A(R) is or may be any one of those well known in the prior art, and each functions to control the power of the output as a function of fre ⁇ quency.
• the output from the frequency equalizer A(L) is directed to a summing junction C(L) and thence, through an amplifier (L) to the left speaker S(L).
• the output from the right frequency equalizer A(R) is directed through a right summing junction C(R) to a right amplifier (R) to drive a right speaker S(R).
• the left stereo input from L(IN) is directed to an inverting device B(LR) which in ⁇ verts the phase of the signal at L(IN) by 180 .
• the output from the inverting device B(LR) is in turn transmitted through four channels to four time delay frequency equalizers, * designated bl(LR), b2(LR), b3(LR), b4(LR), respectively.
• Each time delay frequen ⁇ cy equalizer, bl(LR)-b4.(LR) has two * functions , first, to change magnitude of the inverted signal as a func- tion of frequency, and secondly to delay the signal by a predetermined amount of time .
• the collective output of the four time delay frequency equalizers bl(LR) through b4.TLR) produces a compensating signal which is transmitted to the right summing junction C(R).
• This left-to-right com ⁇ pensating signal is superimposed over the main right stereo s_ignal output from the right frequency equal ⁇ izer A(R), and this combined signal in turn drives the right speaker S(R).
• the output from the speaker S(R) is a sound pattern corresponding to the combined output from the summing junction C(R).
• the right stereo input signal at R(IN) is transmitted through an inverting device B(RL) which inverts the signal by 180 .
• the output from the inverting device B(RL) is transmitted along four channels to a second set of four time delay equalizers, designated bl(RL), b2(RL), b3(RL), and b4-(RL) .
• bl(RL), b2(RL), b3(RL), and b4-(RL) the function of the se- cond set of time delay frequency equalizers bl(RL) through b4-(RL) is to provide a right to left compen ⁇ sating signal that is transmitted to the left summing junction C(L).
• the compensating signal transmitted to the right summing junction C(L) is superimposed - over the main left stereo output from the frequency equalizer A(L) to provide a combined signal which drives the left speaker L(S).
• each compensating signal is controlled by a related switch, Sw(L) or Sw(R), inter ⁇ posed between the input L(IN) or R(IN), respectively, and the related inverter B(RL) or B(LR), respective ⁇ ly.
• This switch Sw(L) or Sw(R) is illustrated some ⁇ what schematically at Figure 4, where there are three voltage dividing resistors Rl , R2 and R3 in series.
• the switching element ⁇ is open, the signal is delivered to the related inverter B(RL> or B(LR) at a lower intensity, i.e. about six decibels below the level of the signal at L(IN) or R(IN).
• the intensity of the com ⁇ pensating signal is increased to about three decibels below the signal at L(IN) or R(IN).
• the switches Sw(R) and Sw(L) act as "injection switches” to either increase or decrease the intensity of the compensa ⁇ ting signal to increase or decrease the dimension ⁇ alized effect of the sound produced.
• each of the components indi- cated above are conventional components well-known in the electronics art, and each may be provided in any one of a number of conventional forms. For exam ⁇ ple, in a book entitled “Operational Amplifiers, De ⁇ sign and Applications", by Jerald G. Graeme, Gene E. Tobey and Lawrence P. Huelsman, published by.
• the first set of time delay frequency equalizers bl(LR) through b4(LR) is to provide a delayed signal output, the intensity of which is modified as a function of fre ⁇ quency. The manner in which this is done is illustra- ted in the table of Figure 5. It can be seen in
• the output from bl(LR) is delayedby a time increment tl or 110 microseconds.
• the magnitude of the output from tl is equal to the input to the inverter B(LR) up until a frequency of 8 KHz is reached ' , after which the output is Zero.
• the second time delay frequency equalizer b2(LR) With res ⁇ pect to the second time delay frequency equalizer b2(LR),- the time delay t2 is 180 microseconds, the magnitude of the output is similar to the unit bl(LR).
• the third time delay frequency equalizer b3(LR) the period of delay t3 is 370 micro ⁇ seconds.
• the time delay period t4 of- the fourth time delay frequency equalizer b4(LR) is ' .690 microseconds
• component b3(LR) has ' for frequencies up to 200 Hz an output of 3.5 decibels above the input to the inverter B(LR).
• the output is 3.5 decibels above the level of the input to the inverter B(RL) .
• the two speakers S(R) - and S(L) and the person P are in what can be termed a "playing area", with the speakers S(L) and S(R) being at a forward location, and the person P being at a rear location.
• the two speakers S(R) and S(L) are positioned along a base axis 20, and spaced from each other a ' predetermined spacing distance.
• the person P is located at a "listening area 24", which is that area immedi ⁇ ately surrounding the head of the person P.
• the head of the person P is located at a "listening location” which is a location on the longitudinal axis 22 at the ideal listening position for the apparatus .
• the person P has a right ear Re and a left ear Le.
• the sum total of this left-to-right compensating signal is made up of separate signal portions re— ceived in sequence at the input R(IN).
• the invention is so arranged that the overall effect of the compen ⁇ sating signal, being superimposed on the main signal from the frequency equalizer A(L) is not sufficiently great to cause any noticeable degradation of the main signal from the frequency equalizer A(L).
• this combined signal increment i.e. the left main signal with the superimposed right-to-left compensating signal
• the sound emitted from the speaker can be consi ⁇ dered as travelling on two sound path components, one primary path component Ll which is'transmitted to the left ear Le of the person P, and a secondary path component Lr which is transmitted to the right
• the left main sound on path component Ll reaches the left ear Le with no significant inter ⁇ ference, so that the left ear Le hears a substantial ⁇ ly undiminished left main sound resulting from the signal increment passing into the left stereophonic
• That initial reaction would have some element of truth in that the present invention does in a sense eliminate or at least diminish some of the tradition- al functional features of stereophonic sound. How ⁇ ever, that analysis is incomplete since it does not take into consideration the nature of sounds produced by a stereophonic recording.
• This left signal incre ⁇ ment results in an earlier main left sound emitted from the left speaker S(L) , and a delayed compensa ⁇ ting signal being emitted from the right speaker S(R) .
• the compensating sound travelling the path Rr has a cancelling function. However, the compensating sound travelling the secondary path Rl to the left ear is not cancelled out. However, since the compen ⁇ sating sound from the right speaker S(R) is not only delayed relative to the corresponding main sound from the left speaker S(L), but also travels a longer secondary path Rl, the corresponding compensating from sound speaker S(R) reaches the left ear Le sub ⁇ stantially later than the main sound travelling the path Ll. It has been found that this does not cause any significant degradation of the main ⁇ sound compo- nent. (e) Operation of the Invention Relative to
• right and left listening axes extending from the lis ⁇ tening location to the right and left speakers S(R) and S(L) respectively.
• the right listening axis makes a right listening angle with the longitudinal axis, and in a like manner the left listening axis makes a left listening angle with the longitudinal axis .
• the left and right ears of the listener are indicated at Le and Re respectively, and the "ear spacing dis ⁇ tance" is also indicated. For the purposes of this analysis , the ear spacing distance shall be presumed to be 7 inches.
• Figure 8 shows the listening location and the right and left ear Re and Le on an enlarged scale.
• the primary and secondary sound path components indicated at Rr, Rl , Lr and Ll . Since the two speakers are generally spaced from the listening location at a large distance, relative to the spacing distance of the two ears Re and L , for purposes of the present analysis, the left primary and secondary paths Ll and Lr can be considered to be parallel to one another, and the primary and secondary right paths Rr and Rl can also be considered to ' be parallel to one another.
• time delay distance will * be used to denote an increment of distance over which sound will travel during a predetermined delay period.
• the time delay distance would be approximately 1.3 inches.
• This ideal time delay distance is illustra ⁇ ted ⁇ raphically at "x" in Figure 8 •
• the sine value would be between 0.5 and 0.707.
• the range of the ideal- time delay distance would be in the range of between 230 microseconds and 460 micro ⁇ seconds .
• the left ear Le has moved closer to the left speaker S(L) by a distance of "z" which is only moderately less than the distance "y” .
• the left ear Le has in effect moved laterally by an increment of distance indicated at "m” in Figure 8.
• the 'change in the ideal time delay distance should be equal to twice the value 'm' times the sine of the listening angle.
• Figure 9 is a representation quite similar to Figure 8, where "the person's right and left ears Re and Le are shown at the listening location. Let it be assumed that the person moves his head to the right , ' with no forward movement and no rotational movement. Four locations are shown for each ear. The left ear is shown at its ideal location, and then moved to the right by three increments, each increment .. " being equal to .one- quarter of the ear spacing distance. In like manner, the right ear is shown at its original position Re and also at three spaced locations to the right, each spacing being equal to one-quarter of the ear spacing distance.
• the ideal time delay distance * With the left and right ears at the ideal position, at Le and Re, the ideal time delay distance *" remains at the value of the ear spacing distance times the sine of the listening angle.
• the left ear simulta ⁇ neously moves further from the left speaker S(L) and closer to the right speaker S(R).
• Each increment * of change is equal, to the distance increment of lateral travel times the sine of the listening angle.
• the effect of these two increments ' is cumulative, so that the net change in the ideal time delay distance relative to the left ear is equal to two times the lateral movement of the left ear times the sine of the listening angle.
• the left ear By the time the left ear reaches the location of the longitudinal axis (at Le(b)), ' the ear is qually distant from both speakers . Thus , the time delay distance to obtain sound cancellation has been reduced to zero . Further movement of the left ear to the location Le(c), indicates that there is actually a negative time delay distance to obtain cancellation. In other words, the cancelling sound from the right speaker S(R) would have to be emitted before the main left signal was emitted from the left speaker S(L) .
• the ideal time delay distance would increase at the same rate that it would decrease for * the left ear.
• the time-delay distance would be, respectively, one and one-quarter of the ideal time delay distance, one and one-half of the ideal time delay distance, and one and three-quarters of the ideal time delay distance.
• the compensating signal is transmitted over a plurality of spaced time delay increments.
• the selection of these time delay increments was obtained partly analyti ⁇ cally and partly empirically.
• the time delay distance increments for the various time delay increments are given below: time delay • ⁇ zime delay increment distance incre;- (microseconds) ments (inches) tl 110 1.53 t2 180 2.34 t3 370 4.81 t4 690 8.97
• the ear spacing distance is 7 inches, and that each of the listening angles is 45 .
• the ideal time delay distance would be approximately five inches.
• the compensating sound at the time delay increment t3 (which has a precise time delay distance of 4.81 inches) would be the primary cancelling sound.
• the cancelling sound having time delay increments of first t2 , and then tl would come into play.
• the effect of the cancelling sound having a time delay increment of t3 would still be effective as the right ear moves further from the longitudinal axis, but would be diminished somewhat.
• time delay increments can be varied, and the amount of variation will depend to some extent on the relative. intensity of the main signal component and the compensating signal components .
• the ranges are believed to be approximately as follows: • ⁇ time delay time ' distance delay range """ .. increment (inches) tl 1-3 t2 • 2-4 . t3 3-7 t4 6-12
• each combined signal emitted from the summing junctions C(L) and C(R) is directed back through a time delay device D(L) or D(R) back to the input source L(IN) or R(IN).
• the amount of time delay is 800 microseconds , which • is moderately longer than the longest time delay increment of the time delay frequency equalizers b4(RL) and b4(LR).
• the effect of this is to direct the ., . total signal (the main signal plus the compensating signal), back through the system.
• the total signal is not only directed back through the same summing junction, but is also directed through the crossover circuit to the opposite summing junction.
• the reflected sounds should also be compensated for to some extent.
• the stereo speakers are placed on the floor, close to the floor, or possibly in a corner. Accordingly, it is expected that sound will be reflected off the floor and/or walls and be directed to the hearer at a time delay in the order of possibly one millisecond, or so. It is believed that this feedback mechanism D(L) and D(R), being fed back through the system and delayed, at least partially compensate for this reflected sound.
• FIG. 10 The recording apparatus of the present invention is illustrated in Figure 10.
• L(IN) and R(IN) the signal inputs to these terminals L(IN)- and R(i;N) should be stereo signals, such as those produced at the microphones"Ml and M2 of Figure 1.
• One method is to use the recording set-up as indicated in Figure 1, ' and attach the two spaced microphones Ml and M2 to respective input terminals L(IN) and R(IN).
• the two terminals L(IN) and R(IN) receive stereo signals, where there are corresponding sound components in each signal, with time delays and intensity changes between the corresponding components of the signal.
• An alternate method of providing the inputs to the terminals L(IN) and R(IN) is simply to take a stereo recording which is made according to the system of Figure 1, and play this recording on a stereo player. Then, instead"of directing, the signals produced by the player to speakers , these signals are directed to the input terminals L(IN) and R(IN). This method is indicated in broken lines in Figure 4-.
• left and right signals are in turn trans ⁇ mitted directly from terminals L(IN) and R(IN) to left and right frequency equalizers, designated
• Each of these frequency equalizers A(L) or A(R) is- or may be any one of those- well known in the prior ar , and each functions to control the power of the output as a function of frequency.
• the output from the frequency equalizer A(L) is directed to a summing junction C(L) and thence to a stereo recorder.
• the output from the right frequency equalizer A(R) is directed through a right summing junction.
• C(R) to the _ stereo recorder.
• the left stereo input from L(IN) is directed to an inverting device B(LR) which inverts the phase of the signal at L(IN) by 180 .
• the output from the inverting device B(LR) is in turn transmitted through four channels to four time delay frequency equalizers, designated bl(LR), b2(LR), b3(LR) and b4-(LR), respectively.
• Each time delay frequency equalizer, bl (LR)-b4-(LR) has two functions, first, to change magnitude of the inverted signal as a function of frequency, and secondly to delay the signal by a predetermined amount of .time.
• the collective output of the four time delay frequency equalizers bl(LR) through b4-(LR) provides a compensating signal which is -transmitted to the right summing junction C(R).
• This left-to-right stereo signal is superimposed over the main right stereo signal output from the right frequency equalizer A(R) , and this combined signal in turn is transmitted to the stereo recorder.
• the right -stereo input signal at R(IN) is transmitted through an inverting device B(RL) which inverts the signal by 180 .
• the output from the inverting device B(RL) is transmitted along four channels to a second set of four time delay equalizers, designated bl(RL), b2(RL), b3(RL), and b4(RL).
• the function of the second set of time delay frequency equalizers bl(RL) through b4-(RL) is to provide a right to left compensating signal that is transmitted to the left summing junction C(L) .
• the compensating signal transmitted to the left summing junction C(L) is superimposed over the main left stereo output from the frequency equalizer A(L) to provide a combined signal which also is transmitted to the stereo recorder.
• the apparatus of Figure 10 is substantially similar to the apparatus of Figure 3, so the description of the apparatus of Figure 10 will not be carried further.”
• FIG. 2 Let it be assumed that the sound recording made in the stereo recorder by the apparatus of Figure 10 is now placed upon a stereo player which in turn is connected to two speakers LS and RS .
• the stereo player and the two speakers LS and RS can be a conventional player and speakers such as those well known in the prior art.
• the player has the capability of taking one of the signals on the sound recording and transmitting this to one speaker LS to reproduce a sound relating to that first signal,, and to take the second signal and direct it to the other speaker RS to produce a second sound corresponding to that second signal.
• the sounds produced by the speakers of Figure 2 are in this instance substantially the same as the sounds produced by the speakers of Figure 3, so no further explanation of these will be added.

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