EDITOR FOR COMBINING DIGITALLY RECORDED AUDIO SIGNALS

Abstract: An apparatus for editing digitally recorded audio signals in which entry (206) and exit (207) edit points are designated based on a display of data derived from audio signal data proximate to the edit points. The apparatus enables the automatic selection and combination of portions of audio signals on at least two channels (201 and 202) to produce a composite audio signal digitally recorded on a record medium.

Description: Description EDITOR FOR COMBINING DIGITALLY RECORDED AUDIO SIGNALS Technical Field This invention relates to a method and apparatus for editing and combining selected portions of previously recorded audio signals to form a composite record audio signal. Background Art Digital recording of audio signals on magnetic tape has been shown to offer significant performance improvements over traditional analog recording methods.. However, to be fully exploited, all functions of the recording studio should be performed in the digital domain. One function performed in the recording studio is editing. Editing refers to a process where selected audio signals recorded- on separate channels of at least one tape medium are concatenated to form an edited, composite audio signal. In prior art analog systems this is typically accomplished by physically cutting the record medium and splicing appropriate sections of the medium together. This cut and splice technique is virtually impossible to perform successfully on digitally recorded tapes because a splice introduces physical tape distortions which prevent accurate audio signal reconstruction. Accordingly in the digital domain, audio signals are edited by a copying process. Selected portions of the audio signals present on different channels of a record medium are copied onto a separate channel of a medium to produce an edited audio signal. The selected portions of the audio signal are defined by edit points which are designated audio signal data words which define a physical location on the record medium. Typically, an entry and exit edit point will be designated to define each selected audio portion. When the entry point for the selected portion is reached, audio signal data will be transferred by a copying process from the channel on which the audio signal is present to another separate master channel. When the exit point for that selection is reached, the copying process for the selected audio section will be completed and a new audio signal from another channel will be transcribed onto the master channel. The primary problem in defining editing points for digitally recorded audio signals involves the location of a position within the selected audio signals where a splice may be implemented without causing audible distortion of the audio waveforms at that point. Once aurally adequate edit points have been determined, it is further required that the transcribing process be performed precisely at the designated edit points. This synchronization is required because the various audio signals may have been recorded at different times on different record media. One prior art approach to editing digitally recorded audio signals involves copying the audio signals onto a magnetic disk memory where they are manipulated and edited to form a composite or master signal on the disk medium. The principal limitation of this prior art approach is the inability to store more than a few minutes of audio signals on a disk memory. Disclosure of Invention In order to overcome such limitations, the present invention is directed to an editing apparatus and method which permits the editing of long duration audio signals and which provides a means for automatically executing an edit function by synchronizing two media transports and transferring audio signal data precisely at the designated edit points. The apparatus enables a method for editing and combining selected portions of digitally recorded audio signals located on separate channels on a record medium to form a composite audio signal. The method comprises the steps of: First, tentative entry and exit edit points defining selected portions of the audio signals to be edited are designated. In a fully automated embodiment disclosed and claimed in U.S. Patent application S.N. 72,076, filed September 4, 1979, by Messrs. Robert J. Youngquist and Donald E. Davis, the spatial locations of the tentative edit points and the audio signals proximate to the tentative edit points are then stored. Next, a representative of the audio signal surrounding the edit points is displayed, in which the representation is indicative of the average amplitude of audio signal data words. In the present invention, a simplified embodiment is provided wherein the audio signals proximate the edit points are not stored and the representation is an audible display of the audio signal itself. The edit points are then refined by modifying in steps of discrete time intervals of decreasing duration the spatial location of the edit point words, based on the audible display. The spatial locations of these refined edit points are then stored. The selected portions of the audio signals which are defined by the refined edit points are then combined to form a composite audio signal by switching between the channels which store the selected portions of the audio signals at positions defined by the refined edit points. Controller means for accomplishing this method are provided which define, locate and automatically combine the selected portions of the digitally recorded signals at the refined edit points. -4- Brief Description of Drawings Figure 1 is a diagram showing the encoding scheme for recording audio signals in a digital format on magnetic tape medium. Figure 2 is a diagram showing a typical edit performed on one record medium. Figure 3 is a diagram showing a typical edit performed between two record media, and Figure 4 is a block diagram representing the controller means of the present invention. Detailed Description Figure 1 shows a record medium 100 having a single channel 101 of audio signal data recorded thereon. The audio signal data is recorded in frames which are 400 bits long. Each frame 102 consists of 16 data words (Di - Dig). Each data word 103 is 16 bits long and encodes a sample of the audio signal waveform. The data words are separated by 8 parity words (P). Each half parity word (P/2) 104 is 8 bits long and is used for error correction. Each frame 102 of data ends with a 12 bit cyclical redundancy check word (CRC) 105, and a 4 bit sync word (S) 106. These words are used for error detection and synchronization respectively. Edit points which are used to define selected portions of the audio signal recorded in this format are specific audio signal data words within a specified frame on a specified channel of the record medium. Consequently, an edit point indicates a unique audio signal data word at a unique location on the record medium. In one embodiment, the recording medium is selected to be 2.5 cm wide magnetic tape having 31 separate channels of audio signal data and one channel of time code information. A time code channel 107 is shown on record medium 100. Each time code word (TC) contains 80 bits of information, several of which are used to -5- designate the physical location of a particular frame on the recording media. Information is read from or written on the record medium 100 at a rate of approximately 3,125 frames per second which corresponds to a nominal tape speed of 114 cm per second. Figure 2 is a diagram showing a typical edited tape where the record media 200 has 4 audio signal channels 201-204 and a time code channel 205. As shown in the diagram, information from channel 201, 202 and 203 are combined to form an edited composite signal recorded on channel 204. The editing process is accomplished by designating entry and exit points for each of the audio signals. Edit points which correspond to designated audio signal data words are selected for each audio signal channel. For example the edit points for the first channel 201 are shown as entry edit point 206 and exit edit point 207. When edit point 206 is reached, the audio signal from the first channel 201 is transcribed onto the fourth channel 204. When the end of the selected audio portion is reached as indicated by reaching edit point 207, audio signal information defined by edit point 208 on the second channel 202 is transcribed onto the fourth channel 204. When the exit edit point 209 on the second channel is reached, information designated by entry edit point 210 on the third channel 203 is transcribed onto channel 204. In this fashion, a composite audio signal on channel 204 is developed by switching between designated channels at positions defined by the selected edit points. It should be clear from figure 2 that this form of edit is only possible when the selected audio portions have been recorded simultaneously on the same record medium. In many instances, however, selected portions of audio signals may not have been recorded on the same record media and as a consequence will not be available for the editing procedure shown in Figure 2. Figure 3 shows the technique for combining selected portions of audio signals recorded on separate channels of separate record media. In figure 3 a first record medium 300 has separate channels labeled 301 and 302 together with a time code channel (T.C.). The second record medium 303 has audio signal data recorded on separate channels 304 and 305 together with a time code channel (T.C.). The composite or edited master channel is shown as channel 301 on tape medium 300. In this edit, material present on channel 302 of medium 300 and information recorded on channel 304 and 305 of medium 303 are combined on channel 301 of media 300. To perform this type of arbitrary splice, edit points for each of the selected audio signals are defined, and the composite track 301 is formed by selectively combining selected audio portions 306, 309, 312 and 315. This is accomplished by defining entry and exit edit points for each of the selected audio portions. To perform the above described entry and exit edit points 307, 308 for portion 306, are defined. Information is transferred from channel 302 to channel 301 at these edit points. Copying audio portion 309 requires that the two tape media 300 and 303 be synchronized at the entry edit point 310 of audio portion 309. This function is performed by controller apparatus which locates the exit edit point 308 on channel 302 and the entry edit point 310 on channel 304 and synchronizes the tape media at these edit point positions. Once the tape media are effectively slaved together at the edit points, data is transferred from channel 304 to channel 301 when edit points 308 and 310 are reached. When the end of portion 309 is reached by detecting edit point 311, the tape media must again be re-synchronized so that the audio portion 312 defined by edit point 313 and 314 coincide with the exit edit point 311 on the composite channel 301. The tape media are rewound and the speed of the transports are adjusted such that the exit edit point 311 now on track 301 coincides with entry edit point 313 of track 305. When these edit points are aligned and synchronized, data is transferred - - from track 305 to track 301, thus splicing audio portion 312 onto the master channel 301. When the exit edit point 314 is reached, data is transferred from channel 302 indicating by entry edit point 316 and the tape is tran- scribed until exit edit point 317 is reached. It should be clear that long duration edits of an arbitrary length can be accomplished by selectively copying, and if necessary, recopying selected audio portions to compile a master channel. The alignment and location of selected audio portions is governed by a control system which automatically positions and synchronizes tapes at selected edit points. Figure 4 shows the controller apparatus for performing the editing functions. Separate recording media 400 and 401 are trans¬ ported by separate transport mechanisms 402 and 403, respectively. The operation of these transports are controlled by the controller 440 which controls variable speed capstans 405 and 406 via communication lines 409 and 410. Each transport is provided with a position indicator means 407 and 408 which contacts the recording media and provides a continuous record of media position information which is communicated to the controller 440 over communication lines 409 and 410. Read/write means which include multiple channel read and write heads, and associated electronic circuitry 411 and 412 are in contact with the recording media 400 and 401 to read and write digital information onto the recording media. The read/write means associated with each channel of each transport are directly coupled to preselected read/write means of one of the channels of the other transport via interconnect cable 442. Time code information read from the media 400 and 401 is coupled via leads 444 and 446 to the interface 448 of controller 440. The controller 440 further includes a central -8- processor unit (CPU) 450, memory 452 and keyboard 454. In operation, the system operator will place the tape transports in the playback mode and will listen to the recorded audio signals. The operator will then designate the tentative entry and exit edit points for the audio data by pressing an edit locate key on keyboard 454 which causes the tape position location from the position locators 407 and 408 and tape position information as evidenced by the time code via leads 444 and 446 to be transferred into memory 452 associated with the controller 440. Next, a shuttle key on the keyboard 454 is activated to shuttle the tape past the tentative edit points and the audio signal immediately preceding or following the appropriate point is audibly displayed. Optionally, the audio signal data proximate to the tentative entry point is also stored in order to allow audible display of the proximate data independent of the tape. Based on the audible display, refined edit point words are selected and the new spatial locations corres- ponding thereto are stored. This refinement is accomplished by means of sets of keys 456 and 458 on keyboard 454, each set being associated with one of the transports 402 and 403. Each set of keys enables the spatial location of the edit word to be modified in steps of discrete time intervals of decreasing duration, i.e. in steps of 30, 10, 3 and 1 millisecond. The combination of the selected portions of the audio signals defined by the refined entry and exit points are then combined as previously discussed. Accordingly, in operation, the system operator will place the transports in the playback mode and will listen to the recorded signals as in the fully automated embodiment in order to select tentative entry and exit points by pushing the edit locate key on keyboard 454, causing the transfer of the tape position location and the time code information from the controller 440 respectively, as in the fully automated embodiment. Next, -9- the transports are energized to shuttle the tape over the selected spots based on the stored tape position location. As the tape is shuttled, the operator then further selects more desired or refined entry and exit edit points by pressing time advance or retard keys 456 and 458 on keyboard 454 which advances or retards the time, i.e. spatial location of the tentative edit points as appropriate, until no further adjustment is desired. The tape is again shuttled and the audio signals from both channels are replayed in combined form based on the refined entry and exit edit points to provide a preview of the edit signals. In the event this preview indicates that the edit location is still not desirable, the tape is again shuttled and the time advance or retard keys used to further refine the selected entry and exit edit points. When a satisfactory preview is achieved, an edit key 460 on keyboard 454 is depressed, thus causing the controller 440 to combine the signals. Since the designated edit points may be at different locations upon different tape media there is a need to provide high speed search and locate function to quickly locate and synchronize the desired edit points to enable a splice to be made. Once the precise edit points have been designated the controller is instructed to search the tape media for the gross position of the edit point by searching first with the tape position indicators 407 and 408 to locate the approximate point on the media where the edit point is located. Next, the controller 440 reads the time code from the record media bringing the frames containing the edit points into synchronization. The controller instructs a selected transport to vary its capstan speed such that the edit points are synchronized on the two media. At this point, the controller instructs the transports to transfer data between designated channels when the data words corresponding to the edit points are detected. Once the edit points have been reached, the controller switches data between designated channels, which begins the copying process and thus performs the editing process.

Claims: -11- CLAIMS : 1. A method of editing and combining selected portions of digitally recorded audio signals located on separate channels on record medium to form a composite digital audio signal comprising the steps of designating tentative entry and exit edit point words defining selected portions of said digitally recorded audio signals, storing the spatial location of said tentative edit point words, presenting an audible display of said audio signals proximate to said tentative edit point words, modifying in steps of discrete time intervals of decreasing duration the spatial location of said edit point words to establish refined entry and exit edit point words, storing the spatial location of said refined edit point words, and combining selected portions of said audio signals to form a composite digital audio signal by switching between said channels at positions defined by said refined edit point words. 2. A method according to claim 1, wherein said combining step comprises operating on said selected portions of said audio signals to directly rerecord said portions onto another channel of record medium to provide a final edited composite digital audio signal. -12- ι 3. A method according to claim 2, wherein said separate channels are located on first and second record media and wherein said combining step comprises locating said first and second record media to predetermined locations proximate to said refined entry and exit edit point words respectively on each tape such that a first component of said selected audio signal precedes said exit edit point word on one channel and a second component of said selected audio signals follows said entry edit point word on the other channel, synchronizing the motion of both media with respect to associated playback tranducers such that the refined entry edit point word on one of said channels is sensed immediately following the sensing of the refined exit point word on the other of said channels, directly rerecording onto a channel of record medium at least one said selected portion to provide on a single channel of record medium, said composite signal consisting of said both components of said selected portions of digitally recorded audio signals. 4. An editing system for combining selected portions of digitally recorded audio signals to form a composite audio signal comprising, a plurality of digitally recorded audio signals located on separate channels on record medium, read/write means for retrieving and rerecording said digitally recorded audio signals on said record medium, transport means for driving said record medium relative to said read/write means, terminal means including keyboard means for imputting data, for designating tentative entry and exit edit point words defining selected portions of said digitally recorded audio signals and for modifying said edit point words, and timing means for enabling advancing or retarding spatial locations of said tentative edit -13- point words in a plurality of discrete time intervals of decreasing duration to enable refinement of said edit point words during repeated shuttling of said medium relative to said read/write means and presenting of an audible display of the audio signal proximate to said tentative edit point words, means for storing the spatial location of said tentative edit point words, means for presenting an audible display of said audio signals proximate to said tentative edit point words, means for selecting refined edit point words based on said audible display, means for storing the spatial location of said refined edit point words, means for locating and aligning designated channels at said refined edit points, and transfer means for effecting selective data transfer between designated channels at said refined edit point words to combine said selected portions of digitally recorded audio signals to form a composite signal. 5. A system according to claim 4, further comprising means for presenting an audible preview of a proposed edit contructed from selected portions of audio signals from both of said separate channels in which the audible display is merged at said refined edit point words, thereby enabling a further refinement of the edit point by iterative shuttling of the medium, modifying the edit point words and again previewing the proposed edit point. 6. A system according to claim 4, wherein said transfer means comprises means for operating on said selected portions of said audio signals for directly rerecording said portions onto another channel of record medium to provide a final edited composite digital audio signal. -14- 7. A system according to claim 5, wherein said separate channels are located on first and second record media and wherein said transfer means further comprises means for locating said first and second record media at predetermined locations proximate to said refined entry and exit edit point words respectively on each medium such that a first component of said selected por¬ tions of audio signals on one channel precedes said exit edit point word on that channel and a second component of said selected portions of audio signals follows said entry edit point word on the other channel, means for synchronizing the motion of both media with respect to said read/write means such that the refined entry edit point word on one of said channels is sensed immediately following the sensing of the refined exit point word on the other of said channels, and means for activating said read/write means for directly rerecording onto a channel of record medium at least one said selected portion to provide on a single channel of record medium said composite signal consisting of said both components of said selected portions of digitally recorded audio signals.

Inventors: YOUNGQUIST R
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING & MFG CO
Application year: 1980
Main classification: G11B27
IPC codes: G11B27, G11B31