Metrical properties of sound-objects

The position of an object in relation to time streaks is calculated on the basis of some properties introduced now. We use the names of properties as per previous publications. These appear more explicitly in the new BP2 interface.

Property PivBeg means that the streak position is the first MIDI message of the object prototype. PivEnd means the last message. PivCent means the centre. PivBegOn means the first NoteOn. PivEndOff the last NoteOff. PivCentOnOff means the centre of the time-span interval starting on the first NoteOn and ending on the last NoteOff. PivSpec is a general case in which the time offset between the first MIDI message and the streak is specified. These properties are explicitly shown in the dialog Fig.2.

Fig.2 Editing metrical sound-object properties

Fig.2 shows that the pivot location may either be defined absolutely (in milliseconds) or as a percentage of the object's duration. In the latter case, it will be modified according to the current time base of the performance if the object has properties OkRescale, OkCompress or OkExpand.

OkRescale means that this object may be expanded or compressed according to the time base. FixScale means it can't. OkCompress means it can be compressed, OkExpand that it can be expanded. (See explicit representation on Fig.2) Indeed, if OkRescale is true, then all other properties except FixScale are made true. The scaling of an object is expressed by the dilation ratio α. If α > 1 then the sound-object is performed slower than its prototype. The dilation ratio may be confined to a range deemed acceptable for the sound-object (see Fig.2). Periodical sound-objects are handled in a different way, see §2.5.

The value of α may be sent to the MIDI device (before the sound-object is performed) in case the sound processor is able to make sense of it for modifying parameters in synthesis algorithms. (Most commercial synths don't.) The current value of α is encoded logarithmically in range 0.01 to 100, and the MIDI controller value is

so that α = 0.01 will yield 0 and α = 100 yields 128. If you want this value to be passed to the sound processor each time this particular sound-object is performed, then check "Send dilation ratio to controller".

"Relocate at will" ( Reloc) means that the pivot of the object may be located far from the time streak if necessary. "Never relocate" forces location on the time streak. Relocation may also be allowed within specific limits (see Fig.2).