In TabTrax you can play back the drum tab at any speed and if mp3 overlay or mp3 sync mode is enabled, the mp3 audio will slow down or speed up to match the speed of the drum track. However, simply slowing down or speeding up a song is probably not want you want to do because that will also change the pitch and make it hard to understand what is happening with the music.
Fortunately, TabTrax (v4.0.20 and above) and Audacity has a cool feature that allows you to slow down a drum track and mp3 audio and keep the same pitch. When you have an mp3 file assigned to a drum track, you can open Audacity by going to the Controls tab and clicking Audacity.
In ‘Change Pitch…’, choose Percent Change: 100% and hit OK. This will double the pitch and allow TabTrax to slow down the song by 50% while keeping the same pitch. Note that only 50% slowing down is supported in this mode. If you feel that other speeds are necessary, please email me.
Now if you play it back it will sound like the band is on too much caffeine and helium but no problem, it will sound fine when slowed down. Now you need to save that, so go to File menu and choose ‘Export…’. Export the file as mp3 but change the name of the mp3 file by adding ‘-pitch100’.
Now you can close Audacity and go back to TabTrax. On the Controls tab, select ‘Pitch Shift’ in MP3 extras. Now when you change tempo, you will only get 2 choices, 50% and 100%. If you choose 50%, TabTrax will load the audio for THE_SONG-pitch100.mp3 and the drum track and the audio will play back at 50% tempo BUT because of the pitch shift, the mp3 audio will sound the same as the original, only slower.
Note that in all other respects it will be as the original, the tempos, time codes etc. will all be as the original 100% tempo song, only playback speed is altered.
Playing the drum track sound with the slowed down mp3 can sound very confusing. It is probably better to mute the drum track (MIDI) in slow speed mode and just use the mp3 audio and visual clues to find check the drum hits are in the correct position.
There is a video here http://youtu.be/Sg0WK4Ly_Jg that shows slow play in action.