Click button "Produce items..." or type cmd-r. (Old-timers will remember the "Run" command in Basic!). You see messages indicating that BP2 is computing the item. (Don't hurry to read messages: there is a command in the "Windows" menu recalling the latest 30 messages.) Eventually an item will be displayed.

Produce more items in the same way. The sequence shown below is dependent on the random sequence generator, and may not be the same on different machines.

Fig.15 Four items have been produced by "-gr.koto3"

These items are in text format, not conventional musical score notation, but BP2 will later manage to convert them to sounds on the basis of information contained in the "-mi.abc1" sound-object file.

While BP2 is at work it may be interrupted by keeping the mouse button down. A small window appears with "Resume" and "Stop" buttons allowing to continue the job or abort it. "Resume" and "Stop" commands appear in the "Action" menu as well. You may also type cmd-r or cmd-<period>. During the interruption you are allowed to do almost anything, for example edit the alphabet and grammar, change options, etc. This may be necessary if the computation has become too slow and you want to understand why it is taking such a long time: select for instance "Step-by-step produce" and then click "Resume" or type cmd-r . (Note that options are related, therefore if you select "Step-by-step produce" then "Display production" will also be selected.) If the computation is looping you may modify the subgrammar to find your way out. Understandably, BP2 might decide to recompile the current grammar before resuming computation.

Because of this possibility of "doing almost anything" while a process is interrupted, you may sometimes enter into unpredicted situations in which BP2 is not able to resume the process properly. Many unusual situations have already been encountered and are handled by BP2, but it is virtually impossible to check all possible combinations. Therefore if you are in the course of an important process it is safe to start afresh before making radical changes.

Let us assume that a few items have been produced in the "Data" window, as shown on Fig.15. Each item is actually displayed as a single line, more precisely a "paragraph" terminated with a carriage return. You may of course type items yourself if you know the alphabet of terminal symbols recognised by the "-mi." sound-object file.

For the next experiments it will be more practical to use the Control panel (see Fig.14) than to pull down menus. Type cmd-= or select "Control panel" in the "Windows" menu.

Select one or several item(s) with the mouse. Click button "Play selection" or type cmd-p. First, BP2 loads the "-mi." sound-object file whose name is specified on top of the "Alphabet" window. The "-mi.abc1" file is loaded forever except if you make changes in the alphabet, in which case BP2 must look for definitions of new sound-objects which the modified alphabet might be refering to.

After a short while you see the sound-object structure (the musical item) displayed in the graphic window while the resulting sound is played on the MIDI output.

Below is the graphic display of item

_vel(127) _volume(40) b b <<f>> {5,a c b,f - f} a <<chik>> b <<sync>>

which was produced by this grammar.

Fig.16 Graphic representation of sound-object structure:
_vel(127) _volume(40) b b <<f>> {5,a c b,f - f} a <<chik>> b <<sync>>

This graphic is a kind of musical score with objects represented as rectangles. Background blue lines are streaks of the time structure and red arrows mark the pivots of sound-objects. (See §2.1 or §3 of the reference manual; read Bel 1992a for a detailed presentation) A tail-less arrow denotes a relocatable object, i.e. one whose pivot may not coincide with a time streak. If a sound-object is truncated the deleted part is displayed with dotted lines.

Simple notes (see §1.3, §1.11) are also represented with rectangles and with no pivot since they are relocatable.

Note that you can modify colours by selecting "Change colours" in the "Layout" menu, and save the new options along with "-se.koto3" settings. Again, users of black and white monitors should uncheck the "Use color" option in the same menu.

A scale of physical time appears on top of the window. Here the tempo was 400 beats per minute, therefore 400/60 = 6.66 beats per second.

You may change the graphic scale of graphics by selecting "Graphic scale" in the "Misc" menu. You must play the item again so that the effect of colour or graphic scale changes become visible.