On Monday I successfully got my computer to play drums using Reaper. So far it works with a MIDI pro adapter but I have not had any success with a Guitar Hero drum set yet. I have made usable charts for a few Guitar Hero Van Halen songs, Brain Stew/Jaded, Raining Blood, and Tre's Greatest Hits. All of them are able to hit 100% of notes in a song, except for Tre's Greatest Hits, assuming I hit play at the right time in Reaper. It seems that each fill is played back in the game at a different speed than the MIDI file plays back in Reaper so it will take some experimenting to get the right playback speeds, however, it is definitely doable. In my experiments I was able to hit 99% of Cool Solo Pt. 2 on more than one occasion and it was more than likely my timing that prevented it from hitting 100%.
Although Reaper playing back the MIDI files I converted will hit 100% of notes 100% of the time it does not make the achievements as easy as I thought it would. Because of the way Rock Band and Guitar Hero work sometimes notes in fast sections of songs will be missed if the start time of the Reaper playback is not perfectly synced with Rock Band. For some reason it will play the slow part of the song perfectly but as soon as it speeds up it will begin missing entire sections of notes (a similar problem can occur when auto kick is turned on in Guitar Hero in a fast double bass section). Even though this happens when the timing is slightly off, as long as it is synced near perfectly it will hit 100% of the song and unlock the desired achievement.
I had a much more difficult time with Rock Band than I did with Guitar Hero because of the smaller timing window. It took me about an hour to unlock "Louder Than Bombs and Eternity" but I usually unlocked the Guitar Hero achievements on my third or fourth try. I would expect to put 30-90 minutes into each achievement because timing can be quite annoying.
I'm going to try make charts for most or all of the miscellaneous Guitar Hero and Rock Band drum achievements some time this week as well as make a video walkthrough of how to set up and use Reaper to play the MIDI files. For anyone who wants to prepare in advance you will need a MIDI to USB cable, a PC or Mac computer with a free USB port and enough hard drive space to download a free trial of Reaper, and a MIDI pro adapter. I hope to add support for Guitar Hero drums in the future as well. I will make another blog post with instructions when I complete my guide and create some more charts.