Interface Manual: Polaris Structure
The intent of this section is to describe the way the Polaris appears through the computer interface, and to relate the way a computer deals with the Polaris to the way a human performer or programmer deals with the Polaris. A computer has a much greater range of control over the instrument than a human, as it is capable of communicating with it much faster than a human could ever punch buttons. What a human sees of the Polaris' inner workings is a subset of what the computer sees, and it is important to understand both in order to fully exploit the capabilities of the interface.
A person sitting at the Polaris and manipulating the controls on the Chroma's panel has a certain view or the inner workings of the Chroma. This view has the following characteristics:
- There are up to 132 programs in the Polaris' memory that can be called upon at any time, numbered A1, A2 ... K12. Each one can either exist or not exist.
- There are up to 3 logical instruments within the Polaris that can be used to play music with different sounds. Two, the Main Instrument and the Link Instrument, are playable from the keyboard. The third, the Sequencer Instrument, is playable by the sequencer. The Main Instrument always exists, and the other two may or may not exist.
- Each instrument that exists contains a copy of a program that determines its sound. The 132 programs stored in memory do not directly control the sound of anything.
- Selecting a program causes one of the 132 stored programs to be copied into the Main Instrument, and storing a program causes the program within the Main Instrument to be copied into one of the 132 storage locations.
- All creating and editing of programs is done to a copy while it is held in a a logical instrument,and then stored someplace else. The program in any logical instrument can be edited.
- while it is held in
- The performance controls affect both the main and link sounds. The notes played on the keyboard are assigned to the main and/or link sounds according to the link mode and keyboard split.
The Chroma uses the terms "board" and "channel" to refer to the sound generation circuitry. The Polaris uses a single term, "voice," to refer to the sound generation circuitry. Unlike a "board," which can be split into two "channels," a "voice" cannot be split.
The boards in the Chroma are allocated to logical instruments as the instruments are defined. Boards can, therefore, be thought of as being parts of the instruments. In the Polaris, voices are allocated dynamically among the instruments as notes are played. Voices, then, must be thought of as separate entities that are used by instruments, not parts of Instruments.
A computer "looking into" the computer interface port on the Polaris has a much more detailed view of the inner workings of the Polaris than a person sitting at the controls:
- The Polaris can contain up to eight logical instruments. The Main. Link and Sequencer instruments are numbered 0, 1 and 2 through the interface. Although they do not necessarily exist, RAM is reserved for them so that they can always be created if they do not exist. Instruments 3 through 7, however, do not exist until created through the interface. Since RAM is not reserved for them, there is a chance that the creation will fail if the Polaris' memory is too full.
- The inside of the Polaris consists or a number of software "objects" that can be accessed through the interface. There are the 132 program objects, the eight instrument objects and the twelve sequence objects. The computer can create, open, read, write and delete objects in a manner similar to the way disk files are accessed.
When controlling the Polaris from its control panel and keyboard, three sounds can be played at a time. The actions of setting up a link or a keyboard split work just like they do in the Chroma with the following exceptions:
The Link Mode and Link Program Number parameters only take effect when a program is selected from the panel. Using the interface to set the Link Mode in the Main Instrument does not cause the link to be changed.
Performance Control Initialization
When a program is selected from the panel, the Main (and possibly Link) Instrument is defined, and their performance control inputs are initialized as follows:
- The volume input is initialized to its nominal value of 255, as the Polaris does not have a volume performance control. (The Volume parameter in a Polaris program is not a performance control.)
- The pedal input is initialized according to the Pedal Initial parameter in the program. (This parameter is the pedal setting that was in effect when the program was stored.) The physical position of the pedal is ignored.
- The lever and footswitch values are initialized to zero. Then, if the actual controls are not in their zero states, additional commands set the control inputs to the correct values.
The Polaris never generates pressure information (unless its sequencer recorded pressure information received over the interface). If Pressure commands are received, however, they are applied to the Pedal input to each voice. That is, the Pedal related parameters determine how pressure will affect the sound. (If Pedal and Pressure commands are used together, they will fight with each other.)
The sequencer can generate parameter changes on the Sequencer Instrument. In addition. the programming controls can be temporarily connected to the Link or Sequencer Instrument, allowing parameter changes to be generated manually for all three predefined instruments.
When a performer selects a program and then alters a parameter, this change is recorded in the Main Instrument: but not in the original stored program. Therefore, every time the same program is selected, the changes made last time it vas selected are usually not still there. If the computer interface is used to play back several concurrent tracks, each containing parameter changes, each track will play on a separate logical instrument, and each logical instrument contain its own copy of a program. Thus, parameter changes sent to one instrument will not affect any other instrument, even if they were defined by the same program.
Whenever an instrument is defined through the computer interface, the performance control inputs must be initialized. To this end, the Define command includes operands that represent the positions of the levers: pedal and footswitch. There is also a volume operand that acts as a master volume control. The volume is also controllable separately through the use of the Volume command. An instrument's volume is not accessible from the panel.
Unlike the Chroma, when the Polaris generates a Define command, it does not use the lever, pedal and footswitch operands of the Define command. Rather, it sets these to zero, and then, if the physical levers and footswitch are not in their zero positions, additional commands are generated. As mentioned before, the instrument automatically sets its own pedal input according to the Pedal Initial parameter. Therefore, the physical pedal position is completely ignored when an instrument is defined, and no Pedal command ever follows the Define command.
When playing the Polaris through the interface, the computer may use the operands in the Define command to initialize the performance inputs, or it may do as the Polaris itself does and follow the Define command with additional commands that set the performance inputs. The pedal input to the instrument may be initialized in three ways, though:
- If the Define command is followed by a Pedal command, the Pedal command will of course take effect.
- If the Define command is not followed by a Pedal command, but contains a non-zero pedal operand, that operand will take effect.
- If the Define command is not followed by a Pedal command and contains a zero pedal operand, the Pedal Initial parameter initializes the pedal.
Therefore, data recorded from the Polaris can be played back verbatim, and sound the same as when it was recorded. The Pedal Initial parameter allows the playback to function properly even if the recording was made with the pedal all the way back but the playback sound requires that the pedal be all the way forward.