GB2195810A

GB2195810A - Multichannel audio signal reproduction

Info

Publication number: GB2195810A
Application number: GB08624015A
Authority: GB
Inventors: John Goodwin Spencer Ive
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1986-10-07
Filing date: 1986-10-07
Publication date: 1988-04-13
Anticipated expiration: 2006-10-07
Also published as: GB2195810B; GB8624015D0

Abstract

In a multichannel audio signal reproducing method or apparatus, a plurality of audio signals are reproduced from a recording medium 1, the audio signals as reproduced being fixed in time relative to one another, and at least one reproduced audio signal is re-timed relative to at least one other reproduced audio signal by delaying the one reproduced audio signal, the delay being effected by temporarily storing the one reproduced audio signal in digital form in a bit storage device (11) such as a random access memory arrangement (11) (Fig. 2) or a shift register arrangement (21) (Fig. 3). The delay may be controllably variable. An alternative arrangement is detailed involving audio and video signals (Fig. 4). <IMAGE>

Description

SPECIFICATION Multichannel audio signal reproduction This invention relates to multichannel audio signal reproduction.

Multichannel audio signal recording is well known, and it is common for a large number of parallel longitudinally-extending tracks, in each of which a respective audio signal is recorded, to be formed on a magnetic tape. The audio signals may be recorded in digital or analogue form. For example, one known multichannel recording and reproducing apparatus is a 24-track machine in which 24 digital audio signals can be recorded in the respective tracks on a half-inch (approximately 12.7mm) magnetic tape, together with time codes.

When the audio signals are reproduced by a multichannel recording and reproducing apparatus, the reproduced audio signals from the respective channels are fixed in time relative to each other, as they come off tape. However, in the case, for example, of music recording, it may be advantageous to re-time one or more of the reproduced audio signals relative to another or to others of the reproduced audio signals. For example, it may be required to re-time a reproduced rhythm signal slightly relative to other reproduced music signals. Likewise, some re-timing may be advantageous where the reproduced audio signals are to be associated with a video signal.For example, the timing of backing music may require slight adjustment relative to a commentary, or a voice signal may require slight adjustment relative to a video signal to achieve lip-sync, without changing the timing of associated audio signals relative to the video signal.

In such cases the extent of the re-timing required is only a matter of up to a few seconds. Currently such re-timing is, for example, done by dubbing down the audio signal or signals to be re-timed; that is by recording the audio signal or signals from the respective track or tracks onto another machine, and then re-recording with the appropriate delay to make a final recording. Clearly such a procedure is time-consuming, and the re-timing of a substantial number of audio signals requires a large amount of apparatus. Moreover, the effect of re-timing one audio signal relative to another is difficult to check, as the steps of reproducing, delaying, re-recording and re-reproducing generally have to be effected before the end result can be heard and assessed.

According to the present invention there is provided a multichannel audio signal reproducing method comprising: reproducing a plurality of audio signals from a recording medium, the audio signals as reproduced being fixed in time relative to one another; and re-timing at least one said reproduced audio signal relative to at least one other said reproduced audio signal by delaying said one reproduced audio signal; said delay being effected by temporarily storing said one reproduced audio signal in digital form in a bit storage device.

According to the present invention there is also provided a multichannel audio signal reproducing apparatus comprising: means for reproducing a plurality of audio signals from a recording medium, the audio signals as reproduced being fixed in time relative to one another; and a bit storage device for re-timing at least one said reproduced audio signal relative to at least one other said reproduced audio signal by storage of said one reproduced audio signal in said storage device and subsequent retrieval of said one reproduced audio signal from said storage device, thereby delaying said one reproduced audio signal.

Preferably said bit storage device comprises a random access memory arrangement, al though in alternative embodiments it may comprise a shift register arrangement. Preferably said delay is controllably variable, and in specific embodiments of the invention the delay may be controllable up to a maximum of, for example, a few seconds.

Said recording medium may be a multitrack magnetic tape, but the invention is not limited in this respect, and it may, for example, be applied to video tapes where the audio sig#nals are recorded in association with a video signal or in a video-signal format.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows in block form the basic form of an embodiment of the present invention; Figure 2 shows in block form part of a first embodiment of multichannel audio signal reproducing apparatus according to the present invention; Figure 3 shows in block form part of a second embodiment of multichannel audio signal reproducing apparatus according to the present invention; Figure 4 shows in block form part of a third embodiment of multichannel audio and video signal reproducing apparatus according to the present invention; and Figure 5 is a timing chart used in describing the operation of the third embodiment of Fig.

4.

Referring to Fig. 1, a magnetic tape 1 is assumed, for simplicity, to have just two parallel longitudinally-extending tracks 2 and 3 in which respective digital audio signals are recorded, and a time code track (not shown).

When the audio signals recorded in the tracks 2 and 3 are reproduced by magnetic reproducing heads 4 and 5 respectively, the output audio signals supplied over lines 6 and 7 are necessarily fixed in time relative to one another. The requirement is to be able to re time the output audio signals relative to one another, for example by up to a few seconds, and for this purpose variable delay devices 8 and 9 respectively are provided in the lines 6 and 7. Of course, in this very simple example, where just two audio signals are considered, it may be possible to effect the required retim ing with a single variable delay device, but more generally, in a multichannel system, a variable delay device will be required for each channel.

Each of the variable delay devices 8 and 9 is a bit storage device, preferably a random access memory (RAM) arrangement or a shift register arrangement. If it is assumed that the audio sampling frequency is 48000 samples per second, that each sample is coded into a 16-bit word, and that the maximum delay re quired is five seconds, then the maximum number of bits to be stored per channel is: 48000x 16x5 =384x 104.

In the case where a RAM arrangement is used, the maximum number of bits to be stored is more conveniently considered to be: 240x 103x 16 from which it will be seen that the bits can conveniently be stored in sixteen 256 x 1 RAMs, the sixteen bits of an audio sample word then being stored at the same address in the sixteen RAMs respectively.

Fig. 2 shows part of the first embodiment of multichannel audio signal reproducing appa ratus using such a RAM arrangement compris ing sixteen 256k x 1 RAMs 11i to 11 16 The associated circuitry is, for simplicity, shown only connected to the RAM 11,. The first bits from each of the 16-bit audio sample words are supplied serially to the RAM 111 by way of an input 12. A first counter 13 receives a clock pulse signal at the sampling frequency, 48000 Hz in the present case, via an input 14, and supplies the clock pulse signal to the input of a second counter 15. The second counter 15 is presettable under control of a timing signal supplied by way of an input 16.

The counters 13 and 15 are basically simi lar, each counting to a maximum of 256k, so that the outputs derived from their respective stages form write and read address signals respectively for the RAM 111. These address signals are supplied to the RAM 111 via a selector 17, and the output of the RAM 111 is supplie#d to an output 18 by way of a latch circuit 19. The clock pulse signal is also sup plied to a read/write signal generator 20, which supplies read/write signals to the selec tor 17, to the enable input of the RAM 111, and to the latch circuit 19.In this way, the selector 17 is controlled alternately to supply the read address signals and the write address signals to the RAM 111, the RAM 111 is enabled to read and write in synchronism with the supplied read address signals and write address signals, and the latch circuit 19 is controlled to supply to the output 18 only the read bits.The necessary read/write signals can very readily be derived by the read/write generator 20 from the clock pulse signal, and indeed one level of the clock pulse signal may correspond to 'write' and the other level of the clock pulse signal may correspond to 'read'. By re-setting a count in the second counter 15, under control of the timing signal, an offset of the count in the second counter 15 relative to the that in the first counter 13 can be set, and if required varied, so controlling the delay to which the stored audio bits are subjected in the RAM 111.

A respective latch circuit 19 is associated with each of the RAMs 112 to 1116, but as the operations are all synchronous the other circuits described above can be common to all the RAMs 111 to 1116.

Thus by controlling the delays effected by the RAMs 112 to 1116 in this way, all sixteen of the bits making up each audio sample word can be synchronously delayed by an amount determined by the timing signal, so effecting the required delay of the reproduced audio signal relative to another reproduced audio signal which has not been delayed, or has been delayed by a different amount in another similar variable delay device.

Turning now to Fig. 3, this shows part of the second embodiment of multichannel audio signal reproducing apparatus in which the variable delay device is a shift register arrangement. Using the same example as above, the number of bits to be stored for a five second delay is 384x 104. and this therefore is the number of stages required in a shift register 21. The bits of the audio signal are supplied serially to the shift register 21 by way of an input 22, and the output bits are supplied serially to an output 23. A clock pulse signal of frequency 48000x 16, that is corresponding to the audio sampling bit rate, is supplied to the shift register 21 by way of an input 24.

Although the shift register 21 has 384x 104 stages to accommodate the maximum required delay, it is additionally programmable so that it can be made of the effective length necessary to give any required delay up to the maximum. For this purpose a timing signal is supplied via an input 25 to a control device 26, which supplies a plurality of control signals to the shift register 21 to control the effective length of the shift register 21 to that required to result in the delay corresponding to the value set by the timing signal.

To reduce the number of stages required in the shift register 21, the individual bits of the incoming 16-bit audio sample words can be split so as to be supplied in parallel to a plu rality of respective shift registers. For example, each of the sixteen bits in each 16bit audio sample word can be supplied to a respective one of a group of sixteen 24x 104 stage shift registers, the series/parallel operation, so far as the audio sample words are concerned, then becoming somewhat similar to that described with reference to Fig. 2.

In both the above embodiments it has been assumed that the audio signals have been recorded and are reproduced in digital form. If this is not so, and the audio signals are recorded and reproduced in analogue form, then the variable delay device in each channel must be preceded by an analogue-to-digital (A/D) converter and succeeded by a digital-to-analogue (D/A) converter. Such A/D and D/A converters are relatively expensive services, and embodiments of the present invention are therefore preferably used with digital systems, although they can be used with audio systems, particularly where the number of channels is relatively small.

Referring now to Fig. 4, this shows the third embodiment, which is a multichannel audio and video signal reproducing apparatus.

The apparatus comprises a video signal reproducing portion 31 and a multichannel audio signal reproducing portion 32 both under the control of an editor 33. The control is effected by time codes recorded in association with the video and audio signals. In the description that follows it will be assumed that the editor 33 sends first time coded designated T/C1 to the video signal reproducing portion 31 and second time codes designated T/C2 to the audio signal reproducing portion 32. The video signal reproducing portion 31 and the audio signal reproducing portion 32 then operate to bring their reproduction into synchronism with the supplied time codes T/C1 and T/C2 respectively.

In an alternative arrangement, reproduced time codes may be supplied by the video signal reproducing portion 31 and the audio signal reproducing portion 32 to the editor 33, which in this case would be more accurately designated an editor/synchronizer 33, in which they are compared with desired time codes, and the reproduction by the video signal reproducing portion 31 and the audio signal reproducing portion 32 are then controlled to speed up or slow down until the required synchronism is achieved with the comparison time codes generated in the editor/synchronizer 33.

Although shown separately, the video signal reproducing portion 31 and the audio signal reproducing portion 32 may form part of a common machine, and indeed the video signal and a plurality of audio signals may be reproduced from the same recording medium.

The audio signal reproducing portion 32 will now be considered in more detail. It comprises a multichannel audio signal reproducing device 34 including the usual servos for controlling a magnetic medium transport mechanism, for example, a tape transport mechanism, in dependence on a supplied time code.

In operation, the multichannel audio signal reproducing device 34 supplies a plurality of reproduced audio signals such as Al, A2,..

over a corresponding plurality of channels which comprise similar variable delay devices 351, 352, .... respectively. The multichannel audio signal reproducing device 34 and the variable delay devices ....... are controlled by a microprocessor 36 to which the second time code T/C2 is supplied by the editor 33. The microprocessor 36 is in turn controlled from a control panel 37 by operation of which the required re-timing of the reproduced audio signals Al, A2, . . . relative to each other and to the reproduced video signal, designated V, can be programmed by the generation of control signals for supply to the microprocessor 36.

The microprocessor 36 generates respective timing signals for supply to the variable delay devices 35 . . . in dependence on the control signals. The variable delay devices 351,... comprise bit storage devices and are preferably as described with reference to Figs.

2 and 3, more preferably being RAM arrangements as described with reference to Fig. 2.

If each of the variable delay devices 351, ... is controlled to delay the respective audio signal Al,. by zero amount, and the time codes T/C1 and T/C2 are synchronized, then the video signal V and the audio signals A1, . . . will be supplied in the same fixed time relationship one to another as they are when reproduced by the video signal reproducing portion 31 and the multichannel audio signal reproducing device 34.

Referring to the timing charts of Fig. 5, this situation is illustrated by the top five lines, which indicate by the vertically-aligned marks that the video signal V, the audio signals Al, A2,..., and the time codes T/C-1 and T/C2 are in synchronism corresponding to the fixed time relationship on reproduction. In addition to requirements to delay one or more of the audio signals A1, . . . relative to the other audio signals A2, ... and the video signal V, the requirement may arise for one or more of the audio signals A1,...to be re-timed so as to be made slightly earlier in time relative to the video signal V.To permit such advance to be effected, the microprocessor 36 processes the incoming time code T/C2 from the editor 33 to form a third time code T/C3 which is actually supplied to the multichannel audio signal reproducing device 34, and is advanced by DA relative to the second time code T/C2.

Thus: T/C3=T/C2+DA as indicated in Fig. 5; DA being selected to equal the maximum time by which any one of the audio signals A1, . . . may require to be advanced relative to the video signal V.

In a-particular example, assume that the audio signal Al is to be advanced by DA relative to the video signal V, and the audio signal A2 is to be delayed by DB relative to the audio signal V. Then if the delays effected by the variable delay devices 35, and 352 are D1 and D2, respectively: D1=0 D2=DA+DB and these are the delay values which must be set by the respective timing signals supplied by the microprocessor 36 to the variable delay devices 351 and 352.

In the case where such an advance may be required in addition to a delay, then it will be seen that the maximum delay which can be effected by the variable delay devices 35,....must be equal to the sum of the maximum advance and the maximum delay.

Various modifications are of course possible without departing from the scope of the invention as defined by the appended claims.

For example, the duration of the maximum delays effected by the variable delay devices will be selected in dependence on the specific requirements, and the maximum number of bits to be stored in the variable delay devices will depend not only on the maximum delay, but also on the sampling rate and on the number of bits per sample.

Claims

1. A multichannel audio signal reproducing method comprising: reproducing a plurality of audio signals from a recording medium, the audio signals as reproduced being fixed in time relative to one another; and re-timing at least one said reproduced audio signal relative to at least one other said reproduced audio signal by delaying said one reproduced audio signal; said delay being effected by temporarily storing said one reproduced audio signal in digital form in a bit storage device.

2. A method according to claim 1 wherein said bit storage device is a random access memory arrangement.

3. A method according to claim 1 wherein said bit storage device is a shift register arrangement.

4. A method according to claim 1, claim 2 or claim 3 wherein said delay is controllably variable.

5. A multichannel audio signal reproducing apparatus comprising: means for reproducing a plurality of audio signals from a recording medium, the audio signals as reproduced being fixed in time relative to one another; and a bit storage device for re-timing at least one said reproduced audio signal relative to at least one other said reproduced audio signal by storage of said one reproduced audio signal in said storage device and subsequent retrieval of said one reproduced audio signal from said storage device, thereby delaying said one reproduced audio signal.

6. Apparatus according to claim 5 wherein said bit storage device is a random access memory arrangement.

7. Apparatus according to claim 5 wherein said bit storage device is a shift register device.

8. Apparatus according to claim 5, claim 6 or claim 7 wherein said delay is controllably variable.

9. Apparatus according to claim 8 further comprising means for reproducing a video signal.

10. Apparatus according to claim 9 further comprising means to control the reproduction of said plurality of audio signals and said video signal such that said audio signals as reproduced are advanced in time relative to said video signal as reproduced, whereby selection of the delays effected by said bit storage devices on said reproduced audio signals can cause individual said reproduced audio signal derived from said bit storage devices then to be advanced or delayed relative to said reproduced video signal.

11. A multichannel audio signal reproducing method substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

12. A multichannel audio signal reproducing apparatus substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.

13. A multichannel audio signal reproducing apparatus substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.

14. A multichannel audio and video signal reproducing apparatus substantially as hereinbefore described with reference to Fig. 4 of the accompanying drawings.