Thank you IR Master Dave for your response. I downloaded the documents and program you referenced but unfortunately I don't see where the duty cycle is stated for a given protocol. For example, the IrpProtocols.ini file describes the NEC 1&2 protocols as follows:

[protocol]
name=48-NEC1
irp={38.4k,564}<1,-1|1,-3>(16,-8,D:8,S:8,F:8,~F:8,E:8,~E:8,1,^108m,(16,-4,1,^108m)*)\
[D:0..255,S:0..255=255-D,F:0..255,E:0..255]
EFC_translation=LSB comp
[documentation]
This protocol signals repeats by the use of dittos.

[protocol]
name=48-NEC2
irp={38.4k,564}<1,-1|1,-3>(16,-8,D:8,S:8,F:8,~F:8,E:8,~E:8,1,^108m)+ \
[D:0..255,S:0..255=255-D,F:0..255,E:0..255]
EFC_translation=LSB comp
[documentation]
This protocol signals repeats by the use of dittos.

The documentation also states:

1. General principles of IRP notation
1.3 The execution process
...The carrier frequency was described in 1.1. The duty cycle is the percentage of the cycle time that the IR light is on. A carrier frequency of 40kHz means that there are 40000 cycles per second, so each lasts 25μs. If each cycle consists of the IR light being on for 9μs and off for 16μs then the duty cycle is 9/25, or 36%. The frequency varies substantially between one protocol and another and is given in the IRP notation. The duty cycle is a matter for the implementation and is not given in the IRP notation. Duty cycles are typically around 33%. A larger value means that the batteries in a remote control will last less long but the range of the signal will be greater.

14. Execution model
14.1 Introduction
... Also set externally is the duty cycle of the carrier generator. This is typically 33% or thereabouts, but again it is outside the scope of the IRP notation.

14.4 Execution
... By means outside the scope of IRP notation, this binds certain names to values in the global environment and sets the carrier generator duty cycle.

Would you be so kind as to point out where the duty cycle is defined or how it can be calculated in the above NEC protocol examples? TIA

- IR Padawan