Message Creation and Delivery

When a segment is played, most of its tracks generate messages containing information about events that are to take place during playback.

A few tracks send more than one kind of message. For example, a style track sends note messages and time signature messages. In such cases, an application can disable certain kinds of messages in the track. For more information, see Disabling and Enabling Track Parameters.

The performance engine determines when each message is to be processed in clock time. In the case of channel messages, the performance also determines which performance channel gets the message. This information, along with other data—including the message type, its source track, and pointers to the first toolgraph and tool that are to receive it—is stored in the message structure.

Certain messages, such as tempo and time signature changes, are immediately processed and freed by the performance. Other messages, such as notes and patch changes, are placed in a queue and processed in order of time stamp.

Note   There is no guarantee that messages with the same time stamp will be processed in any particular order.

Time signature messages are purely informational. The time signature is built into the segment and cannot be changed.

Ultimately, unless a message has been discarded, it arrives at the DirectMusic output tool, which converts all the data it receives into standard MIDI messages and delivers these to the synthesizer through the port buffer.

For an illustration, see Overview of Audio Data Flow.