6. Interactive control

When the "Interactive (use input)" button is checked on the lower "Settings" dialog (accessed by typing cmd-option space, see Fig.24 in §5.2), BP2 keeps listening to messages received on its MIDI input and may react to them if instructed to do so. It keeps listening even whe it is not doing anything particular such as improvizing music or running a script.

Instructions on how to react are stored in a "-in.<name>" file displayed in the "Interaction" window. The format of these instructions is part of BP2's script language, therefore it is convenient to say that the "Interaction" window contains a script.

Conversely, BP2 produces MIDI messages, some of which may be used to trigger processes on external devices (including copies of BP2). For instance, BP2 is able to start any process when prompted by the appropriate MIDI message. This is possible thanks to the instruction

which will execute the specified script instruction at the time a NoteOn message is received, including running another script if “script instruction” is:

Caution: this instruction will only work if BP2 finds the specified script (or its alias), either in the start-up directory (the one in which you did a double-click to start BP2), or in the latest directory in which a script was found during the current session. Otherwise, BP2 will prompt the user to locate the script.

6.1 When does it react?

BP2 does react to MIDI input provided that (1) it is in the appropriate format, i.e. the message has been declared in the "Interaction" window ("-in.<filename>" file), and (2) both the "Interactive (use input)" and "Use MIDI in/out" buttons on the lower "Settings" dialog are checked (see Fig.24).

The status of these buttons is saved and loaded along with "-se.<filename>" settings files. Each time a project, grammar or data is loaded, their status might therefore change. Also make sure that a file has been loaded to the "Interaction" window, or load it manually if necessary: its name will be inserted on top of the "Grammar" and "Data" windows, so that it may automatically be loaded next time you start the project.

A third condition for BP2 to react to MIDI input messages is that it has free time. Messages are stacked into the MIDI input buffer waiting for BP2 to read them, which it does as often as possible. A delay in the response may be caused by the fact that BP2 was engaged on some more urgent task.

Apart from launching scripts, many parameters controlling BP2's operation may be directly modified via the MIDI input, as demonstrated below.

6.2 The MIDI filter

Checked boxes on the left indicate which types of MIDI messages are currently received by BP2. Some of these messages may activate processes, as we will see later. The right column indicates which messages are transmitted to the MIDI output. Transmission may be necessary if BP2 is part of a chain of MIDI devices -- unless you connect other devices to the "MIDI thru" output of the computer's interface.

If a box is checked in the right column the corresponding box is automatically checked in the left column, because a message cannot be transmitted unless it is received.

Settings shown Fig.25 are the default settings recorded in "-se.startup". If you load project "-gr.koto3" the MIDI filter dialog will display the settings found in "-se.koto3". Clicking the "Reset" button makes it possible to retrieve start-up settings.

BP2 keeps receiving and transmitting messages (at idle time) provided that the "Use MIDI in/out" button is checked on the top "Settings" dialog (type cmd-option space, see Fig.24). If the option is not checked you will be prompted to turn it on when displaying the MIDI filter dialog.

6.3 The "Interaction" window

Suppose that the project "-gr.koto3" has been loaded. Before playing the first item, BP2 loads interactive code file "-in.abc1" that contains the actual information the project needs for external control. The file is loaded just before the first item is played if "Interactive (use input)" is checked on the "Settings" dialog.

This file is actually a script. Instructions appearing in the "Interaction" window belong to the subset of well-formed script instructions. (See the entire set in the "Script" menu.)

The order of instructions in the "Interaction" window is not relevant. The only instructions that should appear on top are "BP2 script" and "Note convention = ..." indicating the convention used for interpreting the following instructions. If another note convention is selected in the "Misc" menu, the content of the "Interaction" window is automatically translated to the new convention, and the second instruction is modified or created accordingly. In this way, interactive files remain consistent with projects using different note conventions.

The compiler checks the consistency of instructions: if for instance the same key or controller is assigned several tasks, an error message will be displayed.

New instructions are entered by pulling down the "Script" menu when the "Interaction" window is active. Slots may then be filled with the required values. Remember that you can enter note names by hitting a key on the MIDI keyboard once "Type from MIDI [toggle]" (cmd-j) is active. All instructions are documented on-line: type cmd-? and pick an instruction in the "Script" menu.

6.4 Distributed improvisation

Interactive controls make it possible for several BP2's and other MIDI devices to collaborate on the same MIDI 'network'. Communication is generally done on a reserved MIDI channel, here for instance channel 15. You must set the MIDI keyboard to channel 15 to be able to interact with project "-gr.koto3".

The first instruction (a toggle command) assigns key F#4 to instruct BP2 to accept or ignore 'Start play' instructions. When BP2 starts improvising, its response to 'Start play' depends on the setting of radio button "Synchronize start" on the "Settings" dialog. (It might also have been changed by script instructions "Synchronize start ON" or "Synchronize start OFF".) It will be changed again by key F#4 channel 15.

The second instruction is the 'Start play' definition itself: BP2 should wait for a NoteOn of key C5 channel 15. If this instruction is missing, then instead of waiting for a NoteOn BP2 will wait for a 'Start' or 'Continue' MIDI message.

Note that this amounts to the same as inserting a performance control "_script(Wait for C5 channel 15)" or "_script(Wait for Start)" in the beginning of each item. However, once defined in the "Interaction" window, the 'Start play' instruction may be deactivated and reactivated by key F#4.

'Start play' is useful for synchronising the beginning of a musical item accurately. The 'start' message may be sent from a MIDI keyboard or from any other MIDI device, including another BP2. For instance it could be (it is!) the 'sync' sound-object terminating every production in grammar "-gr.koto3". With two computers connected to MIDI, you may run project "-gr.koto3" on both and see how they collaborate... Don't forget to set up "Interactive (use input)" on both machines. Then modify the grammars to give an 'individuality' to each one. It works? You've entered the world of distributed improvisation! Can you figure out a set-up with more computers, including humans messing around?

Sending a NoteOn on key C5 channel 15 otherwise prompts BP2 to play an item immediately. If BP2 is still busy computing the item, several flags will be set so that production is terminated as quickly as possible (by-passing all constraints). This is an equivalent of "it's up to you now" signals used by jazz musicians in a band.

6.5 More interaction!

Here are a few hints for using the interactive features of BP2 in a set-up that would comprise several computers with various MIDI software, and human musicians interacting with keyboards or MIDI instruments.

Limitations are mainly with MIDI channels: several channels are required to play different instruments or to connect different keyboards, and a few remaining channels may be assigned to "non-musical" communication. Don't forget to set MIDI devices to OMNI OFF so that control messages are not audible.

instructs BP2 that every NoteOn received on F4 channel 15 assigns a limit value to the computation time of the current item. The limit is a function of the NoteOn's velocity. This is a way to tell BP2 it should come up with an item ready to play before some other process has been completed. (For instance another BP2 is currently playing the preceding item and it is able to figure out its maximum duration.) If v is the velocity of the NoteOn on key F4, computation time may not exceed 472 v (in milliseconds).

instructs BP2 that all keys between C6 and C7 on channel 15 contain a new setting of its time base (and metronome). Here, C6 will set the time base to 10 ticks in 3 seconds, and C7 to 20 ticks in 3 seconds. Keys between C6 and C7 will assign interpolated values.

A 'change tempo' instruction could be imbedded in a particular musical item. Thus, BP2 may instruct its neighbours that the metronome has changed. It may also change its own metronome using "_script(Tempo ... ticks in ... secs)". A good idea is to follow the 'change tempo' instruction with a 'skip next item' instruction using key D4 channel 15 as instructed by

The "Set tempo" controller is a MIDI pedal changing the metronome speed. "Range 4.5" is the ratio between the maximum value and the minimum value. If the controller is in its medium position (64) then the metronome value is the default one.

These instructions allow the setting of control parameters K10 and K1, respectively, by MIDI devices: K10 is set to the velocity of a NoteOn message on key C8, channel 15, and K1 is set to the value of MIDI controller #7, channel 15.

Remember that K1,... are global variables that may be used as weights in grammar rules, arguments of performance controls (e.g. _volume(K10), see §1.10), or comparison values in flags (see §11.2).

6.6 Synchronisation tags

When BP2 finds a tag within a structure of sound-objects it stops everything (including its internal clock) until the input sound-object is received, i.e. the corresponding NoteOn is received or the mouse is clicked. This allows you to synchronise any performance on notes or sequences of notes expected at a particular time.

(Use example in file "-da.trytags") BP2 will play 'a' and 'b' normally, then it will display a message indicating that it is waiting for "D3 channel 15", i.e. the <<W7>> tag. You may actually depress the "D3" key , send a NoteOn or simply click the mouse. BP2 will then continue playing 'c' and hang again waiting for C3, the <<W1>> tag. Now it must stand on the <<W3>> tag, which is not defined, so it prompts you to send a mouse click. Eventually, it will hang on <<W8>>, prompting you to play D#3 or send a mouse click. When done, BP2 will play 'd'.

Synchronisation tags may appear in polymetric expressions as well. Each tag relates to the sound object immediately following it in the same sequence. For instance, the item

yields exactly the graphic output shown Fig.17, but the <<W8>> synchronisation tag will force BP2 to wait for a click or D3 channel 15 before it performs the second occurrence of 'f'. The score table below (Fig.26) makes it clear that the actual interruption separates the item in two parts:

Synchronisation tags are processed as out-time sound-objects but they represent "input" instead of "output" sound-objects. They are also less complex than other out-time objects because they may only be defined as NoteOn's. Undefined tags react to mouse clicks.

Synchronisation tags have been implemented in an earlier version of BP2, at a time scripts and performance controls were not available. A tag like <<W8>> could equivalently be replaced with any variable rewritten as:

6.7 Apple Events -- BP2 in a client-server environment

First of all, BP2 can run in background. For instance, after launching an improvisation or a script, clicking outside BP2 (in the Finder or any other application window visible in the back) sends BP2 to background. This means, it continues its job, including playing sounds through the MIDI output, while the user is doing (almost) anything else on the same computer. Indeed, running several applications implies that enough RAM space is available and the machine is good at sharing resources in an efficient way.

In addition, BP2 responds to Apple Events, i.e. events that enable communication between different applications under MacOS. A typical "client" application is supplied to show the range of possibilities. It is a Claris® FileMaker Pro database named "TryAppleEvents.fm", which contains scripts telling BP2 to do certain things, and explanations on the actual operation.

If it does not work, check Apple Events created by the FileMaker scripts (call "ScriptMaker" in the "Script" menu of FileMaker 3.0). Each event appearing in the script should show "BP2.9.3" as the target, not "<unknown>". If it shows "<unknown>" it probably means that "TryAppleEvents.fm" is not in the same folder as "BP2.9.3", or the desktop needs to be rebuilt.

Note that FileMaker Pro 3.0 does not recognise an application on a remote disk, which means it is not able to send a remote Apple Event even though BP2 would be able to process it.

The environment should be arranged properly when BP2 is used as a server. It is recommended that no client application hides the bottom part of the screen on which BP2 displays messages. The top left part is also useful to see that BP2 has received a "pause" event and is waiting for "resume" or "stop". Doing so, its activity can be controlled without bringing BP2 to the foreground.

The list of currently available Apple Events is found in the on-line documentation under the "Apple Events" entry accessed in the "Frequently aked questions..." dialog. The current version processes events sending musical 'scores' in text format, BP2 scripts, and various tasks such as loading a settings file or changing the note convention.

The client-server technology has tremendous potential. BP2 is so far a unique MIDI software able to handle musical material as text (scores and processes such as grammars or scripts). This data may be stored in the fields of a standard database working as a client of BP2.

Note that in the current version, the target application must already be opened, failing to which the Apple Event won't be able to reach it; in other words, BP2 does not launch applications.

If you are working in the field of graphic animations you may take advantage of BP2 as a server for producing high-quality music on MIDI devices. Random improvisation may be an important asset: each time the animation is played part of the music track will be composed afresh.