MIDI Interceptor comprises the following 3 major functions:-

1. 16-channel Trigger Input Scanner
2. 16-channel Trigger Output Driver
3. MIDI Note to Output Trigger conversion

The combination of these main functions allows the MIDI Interceptor to be 'inserted' in to the control chain of an instrument such as a drum machine (Figure 1) and allows the instruments voices to be controlled by both the instruments own internal controller and an external MIDI controller (Figure 2).

The Output Triggers are all velocity controlled and so will respond to the Velocity byte in the associated MIDI Note message. By default MIDI Interceptor converts the equipments own internal controller trigger detections in to a fixed Velocity value output of 100 unless the ACCENT input is detected in which case the output is set to a value defined by the ACCENT trimpot.
 
Channel #16 is permanently assigned to ACCENT control leaving the remaining 15 channels available for assignment to any MIDI Note and instrument. The period of the trigger-on time can be adjusted using the onboard trimpot (P101) from approximately 2mS to approximately 30mS. The polarity of the triggers can also be set by an onboard jumper to either positive-going or negative-going logic. This setting is implicitly assigned to both the Trigger Input scanner and the Output Trigger driver.

MIDI Interceptor has 16 LED’s which indicate the status of each of the output triggers and are also used during LEARN mode to assist the user whilst programming the board by indicating which TRIGGER output is being programmed.

ACCENT Control

When under MIDI control, the ACCENT output is controlled by either a MIDI Velocity value for any of the Instrument Trigger outputs being greater than 100, or on receiving a Note-ON or Note-OFF message for TRIGGER #16.

When triggered by a MIDI Velocity value of greater than 100, the ACCENT output has the same pulse period as the Instrument Triggers and so will turn ON and OFF in parallel with the Instrument Trigger that initiated the ACCENT.When triggered by a TRIGGER #16 MIDI message, the ACCENT output is turned ON in response to a Note-ON message and turned OFF in response to a Note-OFF message. This mode allows the ACCENT output to be held ON for a controlled period of time.

If the ACCENT control has been turned 'ON' by a #16 command, then the ACCENT output voltage is defined by the ACCENT trimpot. If the ACCENT has been 'triggered' by an Instrument Trigger Velocity being greater than 100, then the ACCENT output voltage is that set by the Velocity value.