G-Area and I-Blocks

Like Csound score files, nGen files contain two main data areas -- the global area (g-area) and the instrument block (i-block). Anything not in an i-block is in the g-area. The g-area is used for global declarations (any global level statements or functions such as tempo statements or macro definitions, etc.) and the i-block for anything relevant to the particular note-list being generated. An obligatory feature of the i-block is the use of "p-fields" (parameter fields). P-fields are analogous to those used in a Csound score file; however, while Csound parses an event at a time, nGen (like Score11) parses by the p-field -- the entire "score" for p2 is read then the entire "score" for p3, etc.. This allows for shortcuts to be used while specifying what will happen to the data throughout the duration of the current i-block. For example, you could specify that the p-field is to "move" over the duration of the entire i-block from a specific starting value to a specific ending value using exponential interpolation. In this manner, you only have to specify the staring and ending value perhaps having several thousand values calculated by the program!

P-fields and MIDI files
If you are going to be creating MIDI files, only 4 p-fields apply:

p2: always the start time of the event (as usual).
p3: always the duration of the event (as usual).
p4: For MIDI this should always be amplitude (0-32767). The value in p4 will be scaled to the range 0-127 automatically. If you happen to use 0-127 it will still be scaled, so stick with 0-32767 always. While this may seem strange, it exists so that Csound files will always convert to MIDI.
p5: For MIDI this should always be pitch. Again these values will be converted to MIDI code automatically. For example, C4 (stored internally by the program as 60), will convert to 48.

All p-fields above p5 will be ignored when creating MIDI files.

I-Block Header
Each i-block must contain a header in the following format:


      i<number> = <# of p-fields> <start time> <X>
      {
      ...p-field data...
      }

where:

<number> = the instrument number
<# of p-fields> = the number of p-fields used in the instrument. This is identical to Csound where P1 is the instrument number. The highest P# used in your instrument will be the number of p-fields in your i-block.
<start time> = the global start time for the instrument (in beats).
<X> = the duration of the instrument. If X is a positive real number, it denotes the number of beats for the duration of the i-block's material. If X is a negative integer, it denotes the number of events that will be calculated. IMPORTANT: If the data in any p-field is less than that specified in the instrument header's duration (total time or number of events), the last value in the p-field will be repeated until the end of the note-list. If this is not desired see the <> delimiters. If you have included too much data in a particular p-field for the duration of the i-block, it will be truncated (a warning message will be printed when this occurs).

I-Block Body
Each i-block must also contain a body, after the header; the body is enclosed in {}s. There are only two obligatory p-fields in the i-block's body: P2 (start times) and P3 (durations). The current limit on the number of p-fields that can be contained within a single i-block is 256 (but this may be significantly more than Csound can realistically accept). The only limitation on the size of an expanded i-block or the number of i-blocks in a file is machine specific memory.