Massive Midi Sync Problem!

Hi!

I got a massive Midi Timing or Midi Sync problem. The file here shows you what´s the problem. The kick is an audiofile programmed in cubase. The bass is an external Midi synthesizer. The bass gets slower an slower… You don´t believe me? Listen to this:

http://www.sendspace.com/file/505iez

Any idea?

I checked 4 computers (Apple Macbook Pro, 2,6 GHz, Intel Core 2 Duo, 4 GB Ram; 2 x Macbook 2 Ghz, Intel Core 2 Duo, 2 GB Ram & Apple iMac 2 Ghz, Intel Core 2 Duo, 4 GB Ram), lots of external hardware synths and samplers (Akai S3200, S950, Roland MKS-80, Roland Juno-106, Ensoniq ASR-10, Waldorf Microwave, E-Mu e4xt ultra, Oberheim Matrix 1000, Roland JV-1080, etc) and 3 different soundcards (Presonus Firestudio, M-Audio Lightbridge & Focusrite Saffire 56). Doesn´t matter which cubase 5 version i use: Always the same problem. If it would be just a simple and constant delay i could work with it. but this way it´s unable to work with…

thx in advance for help!