- One voice per channel
    - channel 0 : tempo & infos
    - ch 0 : soprans
    - ch 1 : alti
    - ch 2 : tenor
    - ch 3 : bass
    - ch 12 : beat
    - ch 14 : accompagnment
    - ...

- In each channel : change time of first event is = 0.000
    - change to 0.001
    - This to avoid problem of fisrt note not played