If you need a certain resolution and a certain speed then it's going to result in a certain number of "counts" per second (ie a certain number of interrupts per second) no matter if you're doing x1 or x4 decoding, won't it?

The difference is that with the former you need an encoder with 4 times the number of cycles compared to the latter. As far as the number of interrupts that micro needs to service there's no difference.

In this particular case we don't know what the speed is but we know that Chris needs (or wants) a resolution of the 0.25 degrees, which his 360CPR encoder will provide with x4 decoding. He could exchange his encoder for one with 1440CPR and do x1 decoding but given that the speed at which the enocder is being moved is the same there will be an equal number of "counts" per second. Doing the x4 decode in software is however a bit more complicated than x1, I'll give you that :-)

As far as noise goes I don't see the difference in running a 360CPR encoder doing x4 decoding and running a 1440CPR encoder doing x1 decoding.

And if using an external decoder circuit, like the one you linked to, there's no need for any interrupts at all, just have two counters count the up/down pulses and differentiate periodically.

/Henrik.