Select by Filter may indeed be the way to go. It all depends on what the dupe events look like, and whether they can be consistently distinguished form events you want to keep. One way to avoid problems is to cut the selected events, and drag or paste them to another track so you can see what your filter "caught" before you delete it. Just make sure the Now time is at the start of the first event before you paste or use Shift+Drag to preserve the timing. Scanning what gets selected in the Event View before cutting may also be helpful.
 
I'm not especially advocating the use of Undupe. I've never had occasion to undupe a track in anger, and have only run the CAL to see how it works. But I am a long-time fan of Select by Filter and its cousin, Interpolate (now Find/Replace).

Yes Interpolate was a good tool. Good tip to add the drag and paste step as well - I neglected to mention it, thanks.

I often encounter the same problem Pete.It would be brilliant to have a cal script that will delete duplicate notes of different lengths (ie, they have the same start time but note length varies) Surely this is not that much of a programming jump from undupe?

trnfoot
I often encounter the same problem Pete.It would be brilliant to have a cal script that will delete duplicate notes of different lengths (ie, they have the same start time but note length varies) Surely this is not that much of a programming jump from undupe?

I haven't looked at the script, but I just did a quick test and Undupe worked on notes with different durations. It appears it's programmed to delete the later of two notes of the same note number that start within the defined window (i.e.. ± half the window size).
 
But it left behind the first dupe event in the clip so it's got at least one issue with that scenario.
 
EDIT: I originally thought it deleted the shorter of two events, but it appears it deletes the later of two events. It would be easy to add more rules and user choices to it. But since I have no use for it, myself, I won't be the one to do that.

Joden your Edit>select suggestion is the right way to go, but if you don't know the durations of notes that in some instances, you cannot see then it's a bit difficult to set the parameters. If for some unknown reason one midi track of the same instrument and same channel has been merged on top of an existing track, how do you remove all the notes behind which are of varying start points and durations? Just to qualify my dilemma, I have been programming backing tracks for my various bands since the eighties, when sequencing and MIDI were first born (no Internet). Dinosaurs walked the street and .... just kidding. The fact is that I don't have to spend many hours programming a song if I can find a decent midifile on-line. Now, there are some amazing midifiles out there but all too often there are some that are a joke. Then there are those that are pretty good and worth fixing, but this is where the hidden note issues come in. I always say "don't re-invent the wheel". This post has gone way past the point but back in the day I had an MC500 sequencer running every keyboard that I had in my studio including a Roland S10 sampling keyboard. Those that weren't midi had a mono CV (control voltage) connection which required a midi to CV interface. My first midi module, a Roland MT32 and a Roland MC-202 handled additional instruments and The Roland TR-505 drum machine did the percussion. I remember programming Ultavox's 'Vienna'. The result, lots of analogue gear all going through various amps. Fat, fat, fat is the only way to describe it. 
Melancholy Pete :)

TBH Pete, with all that experience and knowledge I am a little surprised you are even posting...MIDI is pretty much the same as it always has been (with some additional functions in GM2). To be blunt, if you have accidentally merged two tracks with the same channel (very unusual) and the same instrument, and you want to "undo the damage" I think you are, essentially, screwed!
 
You could try re-downloading the SMF, and extract the relevant tracks to import into your project...unless of course you kept a copy of the original  

petgod1
If for some unknown reason one midi track of the same instrument and same channel has been merged on top of an existing track, how do you remove all the notes behind which are of varying start points and durations?

Hmmm... maybe I need to start writing in all caps.    Undupe,CAL will do this for you. It's "dumb" in the sense that it pays no attention to duration, and always deletes the later of two notes. But if the originally merged tracks are so similar that they can't easily be de-duped manually, using Select by Filter, this is probably okay. I'd have to see exactly what you're dealing to come up with a full solution that might involve multiple steps/phases.

Well what I was alluding to was the fact that it may well have been there in the downloaded file. Admitted, I could have stuffed up and inadvertently done it myself. I do not now work on stage with midifiles. Everything is bounced down to audio. That said, the thing is, when I am hours into a project and come across the hidden notes I need to find a way of sorting it out. The question is how do I delete one layer? Common sense tells me that if it's merged, how can you? Perhaps if you could split the overlaps then at least I could make a decision on what to keep. Event view can show notes on the same track having different midi channels assigned but Event filter doesn't give you a midi channel filter. I post here never being scared to ask a question in the hope that I may get a resolve, then move back to my project and perhaps saving myself a long time looking for an answer that doesn't exist
Pete.

Hey brudlefly, even if you write in caps, "there's none so deaf as those that will not hear"- LOL. Seriously though, Undupe was always my first choice, so important that I have my own keybinding for it. It's what to do when that doesn't work.

petgod1
Event view can show notes on the same track having different midi channels assigned but Event filter doesn't give you a midi channel filter.

The discussion seems to be getting a little circular. If the parts are on different channels, Select by Filter will separate them in a jiffy. And the effect of Select by Filter will show up in the Event List and PRV as highlighting that will help you determine if the settings are picking up what you need.
 
At this point, I'm really curious to see the clip that's posing all these challenges. Any chance you could post a copy somewhere? Or P.M. me, and I'll give you an e-mail address.