A Microcomputer-Based Conducting System
Contents
1. Ker Buxton Reeves Fedorkow Smith and Baecker 9 Fig 3 The synthesizer with disk drive and microcom puter CPU photo credit Robert Hudyma nighan and Ritchie 1978 on the more powerful PDP 11 45 The importance of this in terms of the efficiency of software development was all the more pronounced in that it allowed us to continue using the software tools available under the UNIX operat ing system Ritchie and Thompson 1974 The mi crocomputer is physically housed in the same cabinet as the digital synthesizer A sense of the size of the system can be gained from Fig 3 which is a photograph showing the synthesizer microcompu ter and floppy disk system The File System One of the consequences of having a portable system is that some nonvolatile storage medium is required in order to be able to bootstrap the system as well as to retrieve programs and musical data One alterna 10 Fig 4 Integration of com position and performance systems Composition PDP 11 45 Control Computer Transd ransducers High Speed Parallel Direct Memory Access Interface Performance LSI 11 2 SSSP Digital Control Microcomputer Sound Transducers Synthesizer tive is to simply save a core image on a serial storage device such as a cassette or cartridge tape machine While this provides a workable inexpensive alterna tive Buchla and associates 1978 it has two prime disadvantages it is slow and it2. During this process the screen is continually updated with the current value and the results can be heard simultaneously There is then an im mediately accessible virtual potentiometer available for each continuously variable parameter without any special purpose hardware Pots can be added moved or scaled using this technique without any physical change to the system The technique is direct fluent intuitive inexpensive and only re quires use of one hand Finally it clearly is adaptable to many other control applications not the least of which is digital sound recording and mixing 6 In order to prevent values at the top of the screen from being discriminated against in terms of dragging room the mapping of the tablet coordinates to screen coordinates leaves a margin area at the top of the tablet coordinate space Indirect Control Triggers Manual Triggers One shortcoming of the control techniques described in the preceding sections is that they only allow one parameter to be changed at a time The deficiency of this can be seen in contexts such as unison starts starting more than one score with a single gesture In the case of the on off param eter the way around this problem is to allow several scores to be started by firing a single trigger The use of such a trigger can be considered in two phases The first is the set up phase the scores to be fired by a particular trigger are grouped together T
3. W Buxton W Reeves G Fedorkow K C Smith and R Baecker Structured Sound Synthesis Project Computer Systems Research Group University of Toronto Toronto Ontario Canada M5S 1A4 Introduction The subject of this paper is a portable micro computer based performance system that we call the conduct system 1 This system was de veloped at the University of Toronto as part of the research of the Structured Sound Synthesis Project SSSP Buxton Fogels Fedorkow and Smith 1978 The system built around a microprocessor control ling a digital sound synthesizer had its genesis in the earlier conductor system of Mathews Mathews 1976 That is it is a system that allows the per former to interpret or conduct precomposed score material rather than a system on which the prime performance task is to articulate each individual note as is the case with conventional instruments In the remainder of this paper we shall provide a description of the microcomputer based conducting system concentrating on aspects of the human interface and the control structure In addition we shall discuss what we see as the relative strengths and weaknesses of the system based on our experi ence with it in both the laboratory and the concert hall We shall begin however by relating our work to that of others in the field and by discussing the general issues of the problem Background The past three decades have seen an ever increasing
4. interest in electroacoustic music Battier and Arveil ler 1978 Buxton 1977 Cross 1976 To date how 1 This paper has grown out of an earlier one Buxton Reeves Fedorkow Smith and Baecker 1979 which was presented at the 64th Convention of the Audio Engineering Society While certain parts of the text are the same the bulk of the paper has been rewritten and expanded to better represent the current state of the system and the interests of the readers of Computer Music Journal A Microcomputer based Conducting System ever most compositions Davies 1968 Melby 1976 have been studio productions that are performed by tape playback in a concert hall This situation is largely due to the available hardware s limited abil ity to provide adequate real time control over musical complexity The advent of the voltage controlled synthesizer Moog 1965 saw the beginnings of a change in this situation but it has only been since the recent introduction of digital technology that the full potential of the performance situation shows hope of being realized This was first seen in portable hybrid systems such as those of Buchla 1978 Ko brin 1975 and Bartlett 1979 More recently all digital performance systems have been introduced and successfully used in concert New England Digi tal 1978 The implied notion of performance imbedded in these systems is an important consideration in their comparison In this regard
5. one basis for distinction is the amount of real time musical decision making supported performance by tape recorder and impro visation on a conventional instrument represent two extremes Given this basis a second criterion for distinction is the structural Jevel that can be affected by this decision making That is where does the enabled decision making fall in between the global decisions affecting high level structures and the low level decisions affecting individual notes The role of the conductor in a symphony orchestra is an example of the former the role of an instrumentalist within that orchestra is an example of the latter _ Finally in discussing electronic systems that may be programmed to have a certain amount of musical intelligence we can introduce one more criterion 2 The discussion that follows owes much to conversations with Max V Mathews of Bell Telephone Labs Murray Hill New Jersey during his visit to Toronto in the spring of 1978 3 To use terminology derived from linguistics Chomsky 1972 at what levels is decision making facilitated in terms of the deep and surface structure A Microcomputer based Conducting System Fig 1 Three dimensional space used to characterize performance systems Distribution of decision making Level of decision making Amount of decision making for distinction physically where does the decision making take place That is how is th
6. 7 Note that in typing alphabetic data any nonalphabetic charac ter functions as an alternative to the return character Buxton Reeves Fedorkow Smith and Baecker 11 Fig 12 Summary of group control codes TRANSDUCER TYPED VALUE slider 1 slider 2 x mouse y mouse ramp a ramp b ramp c ramp d ma DTP Ne of that increment In the example given ramp a will provide an increment of 1 every 5 time units ramp b will provide a decrement of 2 Thus a simple mecha nism is provided which enables the parameter to be dynamically varied in a controlled manner while leaving the hands free for other purposes A sum mary of the special characters used to specify each transducer for the purpose of group control is shown in Fig 12 Negative Groups The final new concept to be in troduced concerning groups is the notion of a nega tive group When specifying that a variable such as articulation is to be controlled by a particular group one has the option of prefixing the group number with a minus sign The effect of this is that when the members of group n are incremented members of group n are decremented by the same value The control structure thereby provides a built in facility that allows cross fades to be controlled by a single transducer Duration can vary inversely with tempo richness with amplitude and the whole process in dependently of which transducer is controlling the group Additional Perfor
7. Unlike most users of such terminals we do not interact with the system by typing com mands and having them scroll by rather data and controls are spatially distributed on the screen in much the same manner that knobs and dials are distributed on a mixing console Because each datum has its own specific location and all data are constantly displayed it is easy for the operator to verify the current status of the system and as shall be seen effect transformations on the data It is the coupling of the CRT with the graphics tablet that enables us to exploit the full potential of this use of the display While the terminal does not include graphics capabilities it does have one im portant property it has an addressable cursor Thus the CRT cursor which we shall henceforth refer to as the tracker can be made to follow or track the relative position of the tablet cursor This is seen in Fig 6 for example where the cursor is posi tioned on the upper right hand corner of the tablet and the tracker on the upper right hand corner of the display Mounted on the cursor which is shown in detail in Fig 7 are four buttons In the remainder of 5 The graphics tablet used is a BIT PAD1 manufactured by Summagraphics Fairfield Connecticut The terminal made by Volker Craig of Waterloo Ontario is a standard alphanumeric CRT with addressable cursor The slider box contains two continuous motion treadmill like devices manufactured by Alli
8. de veloped at the University of Toronto as part of the research of the SSSP It is an all digital device capa ble of generating complex high fidelity audio sig nals according to well known synthesis techniques including additive synthesis Moorer 1977 VOSIM Kaegi and Tempelaars 1978 frequency modulation Chowning 1973 and waveshaping Le Brun 1978 Arfib 1978 Through the use of time division mul tiplexing it functionally achieves 16 oscillators each of which has a sampling rate of 50 KHz The output of these oscillators can be routed to one of four audio output channels The Computer In selecting a computer upon which to base the system we were guided by the constraints of cost effectiveness portability and a reasonably high computational bandwidth While existing 8 bit mi croprocessors were compact and affordable from a hardware point of view they had neither the re quired computational power nor the software tools we felt were required This latter point was of par ticular importance in terms of cost effectiveness from the software point of view We already had a large investment in software running on our PDP 11 45 DEC 1973 so the optimal choice would be downward compatible with our existing system We chose the DEC LSI 11 2 DEC 1976 Not only did this allow us to run existing programs on the smaller processor but it also enabled us to continue writing all new software in a high level language C
9. directly controlled as a single unit The approach taken is conceptually similar to the use of a submas ter control in a conventional audio mixer As with on off switches associated with each variable is a control field that is initialized to or null This is diagrammed in Fig lla Any variable can be con trolled by any one of eight group controls numbered 1 to 8 Group setup takes the form of pointing at the control field and indicating the group number either by typing or by using the last typed technique This is illustrated in Fig 11b where the tempo and ar ticulation of both scores has been assigned to group 2 the octave of test 1 to group 1 and the amplitude of both scores to group 3 One task remains to complete the setup phase a transducer must be assigned to control each group to be used This additional level of indirection is im portant in that it allows any group to be controlled by any single transducer and a single transducer to control more than one group Group Control Transducers There are currently eight transducers available as group controllers They fall into three generic types sliders 2 the cursor as mouse x and y and software ramps All transducers have one important quality in common they are all motion rather than position sensitive devices That is they increment or delta modulate the parameters they control The instantaneous value or type of the individual parameters be
10. makes random access file oriented input output very inefficient Since the design of our data structures Buxton Reeves Baecker and Mezei 1978 is highly file oriented we felt that this solution was not accept able For the concert situation therefore we chose to adopt the more expensive but efficient use of floppy disks One important benefit accrues as a result of com bining file oriented approach and matching the PDP 11 45 and LSI 11 2 processors This is seen in the laboratory environment in which the small portable performance system can be integrated with the larger more powerful composition system Fig 4 The basis of this integration is a specially de signed high speed parallel direct memory access DMA link between the two machines From the point of view of the composition system we can make use of all the resources available on the power ful but time shared PDP 11 45 while guaranteeing the integrity of the music s timing by using the LSI 11 as a dedicated slave processor servicing the synthesizer In this case the control transducers of the performance system are left unused From the viewpoint of the performance system we can 4 The DSD 440 dual drive system made by Data Systems Design is used for disk storage A Microcomputer based Conducting System Fig 5 The studio working environment photo credit Robert Hudyma down line load the conduct system from the PDP 11 45 and run the LSI
11. son Research Inc of Nashville Tennessee with electronics of our own design All three devices communicate with the host through standard RS 232 serial interfaces Buxton Reeves Fedorkow Smith and Baecker 11 Fig 7 The four button cur sor this paper they shall be referred to as the Z button and buttons 1 3 When the tracker is placed in a particular position different events can be generated depending on which button is depressed This is a useful interaction that cannot be realized using for example a stylus or lightpen without using a sec ond hand In summary the benefit of our particular choice of transducers is that we can effectively employ tech niques derived from interactive computer graphics on a relatively inexpensive system We feel that the resulting notion of downward as opposed to upward compatibility is one of the most important concepts demonstrated by the system The Nature of a Conductible Score We have stated that the main motivation for de veloping the system was to provide the musician with a tool that would enable precomposed scores to be conducted in performance The next step in de scribing the system is to clarify what is meant when we talk about scores A score is named group of notes that has been previously composed using a composing tool such as scriva Buxton Sniderman Reeves Patel and Baecker 1979 The score may con sist of a single note or a more complex structure
12. 11 as a stand alone processor Most importantly however the LSI 11 can then via the DMA interface use the file system of the PDP 11 45 as if it were its own The user can thereby avoid making redundant copies of files on floppy disks until it is certain they are wanted in concert The composer can compose using the most powerful resources available then immediately interpret that composition using a system optimized for that purpose Furthermore the systems programmer can write compile and debug software on the more powerful PDP 11 45 then easily down line load it into the LSI 11 2 for testing At any time copies of files may be made on floppy disks so that the system can function at remote locations where the umbili cal cord to the PDP 11 45 must be broken The physical proximity of the work stations of the two systems can be seen in Fig 5 a photograph showing the LSI 11 conduct station in the foreground and the 11 45 s graphics display in the background Control Transducers The control transducers used by the system are dia grammed in Fig 6 These transducers consist of three main devices a terminal a tablet and slider box 5 Fig 6 The control trans ducers CRT screen tracker Cursor sliders The terminal employed is a conventional al phanumeric cathode ray terminal CRT It has a typewriter keyboard on which messages can be typed and a video display on which data can be presented
13. D 21 Le Brun M 1978 Digital waveshaping synthesis J Audio Eng Soc 27 250 266 22 Mathews M V 1976 The Conductor Program Paper presented at the First International Conference on Computer Music October 1976 at MIT Cambridge Massachusetts 23 Melby J 1976 Computer music compositions of the United States 1976 Beverly Hills California Theodore Front 24 Moog R A 1965 Voltage controlled electronic music modules J Audio Eng Soc 13 200 25 Moorer J A 1977 Signal processing aspects of com puter music a survey Proceedings of the IEEE 65 1108 1137 26 New England Digital 1978 Synclavier instruction manual Norwich Vermont New England Digital _ Corporation 27 Reeves W Buxton W Pike R and Baecker R 1978 Ludwig an example of interactive computer graphics in a score editor Proceedings of the 1978 International Computer Music Conference ed C Roads 2 392 409 28 Ritchie D and Thompson K 1974 The UNIX time sharing system Communications of the ACM 17 365 375 Buxton Reeves Fedorkow Smith and Baecker 21
14. Z button will cause the score whose name appears at the top of the reserve list window to replace it To use Fig 13 as an example pointing at the name jig and depressing the Z button will cause it to be replaced by bass At the same time all variables associated with that score are set to their default values Therefore to access any score on the reserve list one need only scroll through the list until that score s name appears at the top of the window The active list may thus be updated without dis turbing any other scores that may be playing An important point is that there may be more than one instance of a particular score on the active list at any given time Each instance of the score may have a completely different set of transformations affecting it and all may be playing simultaneously This is illustrated in Fig 13 by the three instances of the score treb Significantly regardless of the number of instances of a particular score there is only one copy of that score in primary memory This is an impor 8 The use of instances is further explained in Buxton Reeves Baecker and Mezei 1978 A Microcomputer based Conducting System Fig 13 The complete screen as seen by user SCORE EVE TEMPO ARTIC testl 1 66 2 68 2 test2 o 66 2 60 2 jig 66 2 6G 2 mel Gf 6 2 6G 2 treb p 6g 50 treb Ao 6 6 treb apo 68 126 rotten 0 60 69 GROUPS TRIGGERS Gi sldri TS a Ge sldr
15. ability of the sys tem there are still inadequacies with the control structure First we chose to limit the number of transducers to be somewhat in accord with the bandwidth of which a human operator is capable However we are still not happy with our ability to switch the context of the transducers and thereby enable this bandwidth to be fully exploited Addi tional transducers such as piano type keyboards and touch sensitive devices the use of presets and the use of cross fades are also being explored in order to improve the user interface Two other major problems are the limited address space and computational bandwidth of the mi crocomputer One solution we are exploring is the use of a two processor system one devoted to the user and file system the other devoted to the syn thesizer This would allow score data to be buffered in during performance without spurious effects as well as give us increased computational power Other processors with a larger address space are also being considered however we still want to main tain software compatability with the PDP 11 45 Concerning computational bandwidth one problem is that all envelope interpolation is done in software 20 box CRT terminal and graphics tablet cursor with buttons in hand Fig 15 The microcom puter based conducting system in action From left to right W Buxton slider there being no ramp generators in the synthesizer Significant be
16. an be reset to its default by placing the tracker over that parameter and depressing button 2 Dragging Perhaps the most effective technique for directly modifying the value of a variable is the technique we call dragging This is a direct approach analogous to reaching out and turning a knob on a console With dragging the tracker is placed over the variable to be updated By moving the cursor in the vertical y domain while holding down the A Microcomputer based Conducting System Fig 10 Examples of trigger usage SCORE 8VE TEMPO ARTIC AMP testl g 6 68 teste 68 698 E 1 RICH CYCLE ON OFF g 1 O uis a Parameters including the control fields for remote triggering SCORE 8VE TEMPO ARTIC AMP RICH CYCLE ON OFF testi 60 60 1 9 test 60 68 1 9 b The same two scores with trigger 9 linked to each SCORE 8VE TEMPO ARTIC AMP RICH CYCLE ON OFF testl 60 60 1 1 9 test2 6 60 1 1 9 T9 T1 c The same two scores playing after a unison start triggered by firing T9 shown for the first time If the value 10 was in the control field rather than 9 the scores would fired by firing T10 SCORE B8VE TEMPO ARTIC AMP RICH CYCLE ON OFF testi 6 62 1 1 9 teste 6 68 1 4 9 T9 T1 d The flip flop nature of triggers Firing T9 will cause test 1 to stop and test 2 to Start Z button the value is in effect dragged up or down
17. e from how it was originally notated Richness RICH This parameter enables us to transform the timbres of the notes from the way they were originally de fined The effect is similar to that of having an adjustable filter affecting the signal generated by a score In the case of the conduct system the effect of adjusting the parameter is intimately linked with the technique of sound synthesis employed For cur AMP Fig 9 Simplified display of an active score s attributes RICH CYCLE ON OFF 1 rent purposes the synthesis technique used is fre quency modulation FM Chowning 1973 The ef fect of the richness parameter therefore is to scale the specified index of modulation affecting the number of spectral components and henc the timbre of individual notes Cycle CYCLE The function of this parameter is to enable the per former to specify what occurs when a playing score comes to its end There are two options available the score will stop or the score will repeat This latter case we call cycle mode Thus the cycle pa rameter is a binary switch specifying whether the score is in cycle mode or not On Off ON OFF The seventh parameter is another binary switch used to control whether the score is on or off When the value is set to 1 the score begins is triggered when it is changed to 0 the score stops and resets Techniques of Control General At all times the status of each active sc
18. e real time decision making distributed between the musician and the machine Bartlett s system is a good exam ple of musical decision making being divided be tween the two Together these three criteria define a three dimensional space Fig 1 that can be used to charac terize performance systems In terms of this space like most of the systems mentioned ours enables the performer to exercise a fairly high degree of real time decision making In contrast however the current implementation is optimized so as to express con trol over syntactic structures above the note level The composer performs or interprets precomposed material in a manner analogous to the role of the orchestral conductor rather than articulating the music note by note in a manner analogous to that of an instrumentalist Finally in the implementation to be described all decision making in this process remains with the human performer conductor Architecture A functional block diagram of the system s architec ture is presented in Fig 2 As is shown in Fig 2 the main functional units of the system are the control transducers the microcomputer a file system and the sound synthesizer Fig 2 System architecture SSSP VO LSI 11 2 Digital Transducers Microcomputer Synthesizer File 4 Channels System Audio Output floppy disks The Synthesizer The synthesizer used in the conduct system Bux ton Fogels Fedorkow and Smith 1978 was
19. e2 T12 b GS x 6 G4 a q G5 GG G7 G amp tant feature given the system constraint that all score material must be in primary memory before the start of a performance and that there are only about 16K words of data memory once the program is loaded The Rate Control The Rate parameter seen in the bottom right hand side of Fig 13 is a frequency control for the master clock of the system Lowering its value to a minimum of 0 by typing or dragging speeds every thing up Conversely raising its value slows things down It is a rather coarse control that determines the rate at which the synthesizer is updated with the minimum value resulting in a rate of 50 Hz The main benefit of this control is to overcome the limita tions of the computational bandwidth of the proces sor It enables the user to set the update rate so that the system is able to finish computing the current update data before an interrupt comes requesting that for the next set It can of course also be used AMP RICH CYCLE ON OFF 1 GQ 3 G 1 G 0 8 1 g GO 5 g 1 G 4 1 1 QZ 4 i 1 0 1 GQ RAMPS 5 1 RATE 1 B 4 y g bass joe mel to effect global accelerandos and retards however these are better realized through the use of groups Concluding Comments on the Control Structure The point to understand in considering the control structure is that it supports parallel contro
20. ff respectively When finished playing a score in cycle mode will repeat otherwise it will stop playing and the display will be automatically up dated A score may be stopped at any point during performance at which time it will reset to its begin ning and wait to be restarted A flag that enables a score to pick up from where it was interrupted also exists but has not been made available to the user in the current implementation due to problems of screen density Using an alphanumeric terminal we can only display 24 x 80 characters Continuously Variable Parameters Typing One technique for changing the value of a variable during performance is to position the tracker over the variable and type the new value If the performer wishes to transpose a score up an octave from where it was originally notated he or she need only point at the octave field and type a 1 Alternatively typing 1 will lower the pitch by an octave In either case the change takes place im mediately The screen is updated and if the score is playing the result heard The typing interaction requires two hands one for pointing and one for typing To facilitate this one 14 handed typing certain system specific conventions have been adopted First to avoid the awkwardness of depressing the return key after typing a value any numeric value can alternatively be terminated by depressing any nonnumeric key Second in order to increase the speed
21. for computer music Computer Music Jour nal 2 4 10 20 9 Buxton W Reeves W Fedorkow G Smith K C and Baecker R 1979 A computer based system for the performance of electroacoustic music AES Pre print 1529 j 1 10 Buxton W Sniderman R Reeves W Patel S and Baecker R 1979 The evolution of the SSSP score editing tools Computer Music Journal 3 4 14 25 11 Chomsky N 1972 Syntactic structures The Hague Mouton 12 Chowning J 1973 The synthesis of complex audio spectra by means of frequency modulation J Audio Eng Soc 21 526 534 and Computer Music Journal 1 2 1977 13 Cross L M 1976 A bibliography of electronic music Toronto University of Toronto Press 14 Davies H 1968 International electronic music catalog Cambridge Massachusetts The MIT Press 15 DEC 1973 PDP 11 45 processor handbook Maynard Massachusetts Digital Equipment Corp 16 DEC 1976 Microcomputer handbook Maynard Massachusetts Digital Equipment Corp 17 Hudyma R 1979 Mini UNIX on the LSI 11 Paper presented at the UNIX Users Group Meeting June 1979 University of Toronto Toronto Canada 18 Kaegi W and Tempelaars S 1978 VOSIM A new sound synthesis system J Audio Eng Soc 26 418 424 19 Kernighan B and Ritchie D 1978 The C program ming language Englewood Cliffs New Jersey Prentice Hall 20 Kobrin E 1975 HYBRID IV user s manual La Jolla C M E U C S
22. he second is the actual trigger firing There are ten triggers available in the system Two of them triggers 9 and 10 T9 and T10 can be fired manually Opposite the on off parameter for each score is a control field to which a trigger number can Buxton Reeves Fedorkow Smith and Baecker 15 be assigned This field is initially set to indicating the default no trigger assigned condition This can be seen in Fig 10a A score can be linked to a par ticular trigger by pointing at the control field and typing the trigger nunber Therefore as is illustrated in Fig 10b score test 1 can be linked with T9 by pointing at its control field and typing 9 The second score test 2 can then be grouped to the same trigger simply by pointing at its control field and pressing cursor button 3 using the last typed technique de scribed earlier Specifying the trigger number constitutes the setup phase In order for the scores to be started the trigger must be fired In the case of triggers 9 and 10 this is done by placing the tracker over the appro priate light button T9 or T10 shown in Fig 10c and depressing the cursor Z button All on off switches controlled by that trigger will then change state As is indicated in Fig 10d this means that if one score is on and the other is off and both are controlled by the same trigger firing that trigger will cause the one to switch off and the other to switch on Anywhere fr
23. ing controlled is irrelevant to the transducer s function Values are simply incremented or decremented when the transducer moves Thus any transducer can con trol many parameters all with different instantane ous values without any concern for context The nulling problem which plagues most automated mixdown systems is thereby avoided The resulting ability to rapidly switch the context of a transducer results in a maximum of control bandwidth from a minimum number of physical transducers A Microcomputer based Conducting System Fig 11 The use of groups SCORE 8VE TEMPO ARTIC AMP RICH CYCLE ON OFF testi g 60 6 1 test2 60 60 g 1 GROUPS RAMPS TRIGGERS Gi a T9 G2 b 4 T10 G Cc G4 d G9 G6 G GE a A simplified view of the screen layout showing the control fields marked by the character for both score parameters and groups SCORE amp VE TEMPO ARTIC AMP RICH CYCLE ON OFF testl 1 68 2 68 2 3 1 t st2 Q 6 2 60 2 Q 3 QO 1 0 GROUPS RAMPS TRIGGERS Gi sldri a 5 1 T9 G2 sldr2 bo 2 5 sao T12 GS X C 4 G4 d G5 G6 G7 G8 b The use of groups is illustrated Group 2 is controlled by slider two The articulation and tempo of both scores are members of this group The octave of test1 is the only member of group one which is controlled by slider one The amplitudes of the two scores form group th
24. l functions For example the members of a group can be incremented by moving slider 1 while another value is being dragged up using the cursor A sum mary of the special functions associated with the cur sor buttons is shown in Fig 14 Given the serial nature of most digital computers and given most current programming languages this parallel control is one of the most difficult constructs to deal with in an elegant manner This is one area of research to which we are currently devoting much of our atten tion In the meantime we find it rather ironic that those of us who jumped on the all digital bandwagon are now spending so much of our energy trying to Buxton Reeves Fedorkow Smith and Baecker 19 Fig 14 Summary of cursor button functions CONTEXT SWITCHES CONTROLS change state clear mouse mode gt N A last typed N A clear BUTTON VARIABLES drag lt _ _ x y last typed set default emulate the parallelism inherent in the analog sys tems we were so quick to abandon Conclusions The system as described has stood up well under the abuses of being moved around from concert to con cert One thing is clear such field testing is invalu able for gaining the information required to improve the user interface One simply cannot simulate in the laboratory how the effectiveness of the design is affected by nervousness sweaty hands and so forth While we are happy about the reli
25. labeled on the system s CRT We can now describe each of these parameters in detail Octave 8 VE In composing a score each note is notated at a spe cific pitch By varying this parameter from its de fault value 0 one can cause the score to be per formed n octaves higher or lower than originally notated A Microcomputer based Conducting System SCORE 8VE TEMPO ARTIC demo 60 60 Tempo TEMPO This parameter allows the speed of performance of a score to be altered What is actually being scaled is the time interval separating the start of one note and the start of the next As with conventional music the tempo is specified as a metronome marking indicating the number of beats per minute Articulation ARTIC The previous example demonstrated how the timing between note attacks could be scaled Articulation allows the user to scale the durations of those notes Scaling all the durations by 0 5 for example results in a staccatolike effect while extending the dura tions beyond how they were notated causes a legatolike effect Notice the potential here for com pensating for room acoustics which may be very resonant or dry for example Notice also that tempo is unaffected by this change Timing between event attacks is orthogonal to the timing of event dura tions Amplitude AMP The parameter of amplitude is rather straightfor ward It enables the performer to scale the dynamics or loudness of a scor
26. made up of up to a maximum of about 800 notes 12 Fig 8 Conductible param eters SCORE 8VE TEMPO ARTIC AMP RICH CYCLE ON OFF Scores can be compared with sequences as used in conventional analog systems There are two impor tant distinctions however First each note of a score may be orchestrated with a different timbre Second the structure need not be a monolinear string That is notes may overlap and the number of simultane ous voices may vary between zero tacet and the maximum supported by the synthesizer currently 16 Finally it is important to consider the notion that a composition is made up of a number of parts for which the division of much vocal music into soprano alto tenor and bass serves as an example For our purposes we consider each of these parts as a separate score Therefore in order to conduct the entire composition we must be able to conduct more than one score at a time This we can do the obvious benefit is that we can now express conductorlike gestures such as a little more from the brass and more staccato in the violins By providing a facility to independently conduct several scores simulta neously we have obtained a much needed handle on the scope of conducting commands Conductible Parameters For the time being consider the simpler task of conducting a single score There are 7 parameters of the score that we can affect Fig 8 shows these parameters the way they are
27. mance Variables Score Selection We have already pointed out that the performer may conduct up to eight scores at a time These are what we have called the eight active scores In the course of performing a composition a performer may wish to use more than eight score files Therefore a mech 18 anism has been provided whereby active scores can be replaced by those from a reserve list The reserve list is made up of the set of all scores specified by the performer during the setup phase of the conduct program They are added to the list as their names are typed and they are read into primary memory Once initialization is completed the first eight of these scores will automatically appear on the display as active scores In addition in the bot tom right hand corner of the display there will ap pear a list containing three names This is illustrated in Fig 13 the first complete facsimile of the display shown thus far This list is a window showing the names of the first three scores on the reserve list Using two special keys on the keyboard f and J we can cause the names in the list to circularly scroll up and down thereby enabling us to display the name of any score on the reserve list To have a new score appear in the upper half of the screen where it can be conducted one points to the name of some score that is already there but which can be replaced If the old score is not playing de pressing the cursor
28. nefits could be gained by changing this situation l In conclusion the system has proven to be a reli able musically useful tool a tool that warrants per former investment in practice time In addition the system has shown the viability of considering downward as opposed to upward compatibility as a design alternative That is a system that is able to use pseudographics techniques on a minimal hardware configuration and that runs software that is the same as that run on a host computer has been demonstrated In this regard the choice of using the PDP 11 family of computers has proved to be a good one Finally the LSI 11 is capable of supporting a complete albeit reduced stand alone composition and performance system which can be run under a locally developed version of the MINI UNIX operat ing system Hudyma 1979 Given the poor software tools generally available for microprocessor systems the techniques described here have significant im plications especially for complex applications such as musical performance Acknowledgments In undertaking the work described in this paper we were greatly aided by several colleagues In particu A Microcomputer based Conducting System lar we are grateful for the help provided by Michael Tilson Robert Pike Sanand Patel and Thomas O Dell in implementing some of the software In addition we would like to acknowledge the support of the Computer Systems Research Group Data Base
29. of typing negative numbers the minus sign can alternatively be indicated by depress ing the space bar which is equally accessible from any point on the keyboard and whose physical ap pearance resembles a minus sign These redefi nitions of the keyboard are easy to remember and they significantly improve the bandwidth and relia bility that can be achieved through one handed typ ing The Last Typed Technique While we have at tempted to make typing as efficient as possible in many cases it is not the most appropriate means of communication Often during performance there is simply no time to type One alternative exploits the observation that we often assign the same value to more than one field The system takes advantage of this redundancy by designating cursor button 3 as the last typed button Placing the tracker over a variable and depressing button 3 causes the last value typed to be assigned to that variable Again the display is updated and the effect may be heard immediately Default Set Another often typed value was observed to be the default or normal value for each variable field 0 for all parameters except tempo and articula tion which have a default of 60 These are the values that cause the score to be performed as no tated To facilitate the frequent desire to restore a parameter to its default cursor button 2 has been designated the default button Using the technique seen in last typed mode any variable c
30. om zero to eight scores can be con trolled by any trigger but only one trigger at a time can control a particular score Trigger assignment may be changed at any time during performance and the trigger control of a particular score can be cleared by pointing at the control field and depressing the cursor Z button or button 2 the default button End of score Triggers An important concept that we wanted to incorporate into the system was to allow trigger events to be generated by events in the music itself While this feature has not been im plemented in a general way one type of event in the data can generate a trigger Whenever a playing score comes to its end regardless of whether it is in cycle mode or not it generates a signal that can be used as a trigger These trigger events are numbered 1 to 8 corresponding to the eight scores which may be ac tive at one time Score a can trigger score b and vice versa Complex combinations of score material can thereby be built up either in sequence or in parallel The only constraint is that a trigger is only generated at the normal end of a score not when the score is turned off midway Note that a score can trigger itself although that would be redundant given the 16 cycle switch which is implemented using the trig ger mechanism Groupings of Continuously Variable Parameters Groups Like the on off switches continuously variable parameters can be grouped together and in
31. ore is dis played on the CRT An active score is a score that is currently conductible While several parts or scores may be conducted throughout the course of a per formance only eight scores may be conducted or active at any one time A simplified version of the format in which these data are displayed is seen in Fig 9 As can be seen in Fig 9 there is a field for the score s name as well as one for each of the seven conductible parameters The fields are labeled and the current value of a particular parameter of a score is shown in the appropriate field opposite the score s Buxton Reeves Fedorkow Smith and Baecker 13 name In this case for example both the tempo and articulation parameters of the score demo are set to the default value 60 For the purpose of control consider the conducti ble parameters as falling into two categories switches and variables Like a light switch a switch can be either on or off The two switchable parame ters are cycle and on off The others octave tempo articulation amplitude and richness are all con tinuously variable They are scaling factors which allow parameters to be transformed from their no tated values during performance Direct Control Switches To change the state of a switch the user positions the tracker above the switch and depresses the cur sor Z button The switch immediately changes state and the screen is updated 1 and 0 represent on and o
32. project especially Dennis Tsichritzis and Robert Hudyma The cooperative environment that per vades the Computer Systems Research Group has made the undertaking of this work a joy The research reported in this paper has been undertaken as part of the SSSP of the University of Toronto This research is supported by the Social Sciences and Humanities Research Council of Canada This support is gratefully acknowledged References 1 Alles H G 1978 A portable digital sound synthesis system Computer Music Journal 1 4 5 6 2 Arfib D 1978 Digital synthesis of complex spectra by means of multiplication of non linear distorted sine waves AES Preprint No 1319 C 2 3 Bartlett M 1979 Microcomputer controlled synthe sis system for live performance Computer Music Journal 3 1 25 29 4 Battier M and Arveiller J 1978 Documents musique et informatique une bibliographie index Elmeratto Ivry S Seine 5 Buchla and Associates 1978 User s guide to PATCH IV and the Series 300 Electric Music Box Berkeley Buchla and Associates 6 Buxton W ed 1977 Computer music 1976 77 a directory to current work Ottawa The Canadian Commission for UNESCO 7 Buxton W Fogels E A Fedorkow G and Smith K C 1978 An introduction to the SSSP Digital Syn thesizer Computer Music Journal 2 4 28 38 8 Buxton W Reeves W Baecker R and Mezei L 1978 The use of hierarchy and instance in a data structure
33. ree which is controlled by the x mouse A transducer can be assigned to a group by point ing at the group control field and specifying the transducer identifier Typing 1 while pointing at the control field of group 1 the opposite the label G1 in Fig 11a assigns slider 1 to control that group as seen in Fig 11b Moving the slider upward will increment all members of the group the octave vari able of test 1 in the figure while moving it down ward will decrement all values Similarly we can use the tablet cursor as a group controller In this case relative motion in the horizontal x and verti cal y domain can each be used to control a group This is illustrated in Fig 11b where we have spec ified that motion in the horizontal domain should control group 3 by typing x in the control field opposite G3 As a result all horizontal cursor mo tion that takes place while cursor button 1 is de pressed will affect the amplitude of both scores Al ternatively we could have typed an a opposite G3 thereby specifying that group 3 is to be controlled by ramp a A ramp is a software transducer that pro vides the benefits of an automatic fader whose direc tion and speed can be easily controlled Each of the four ramps as illustrated in Fig 11b is associated with two parameters The first indicates how often in 50ths sec the controlled group s members are to be incremented The second field indicates the size
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