We introduce a time-domain model for the synthesis of attack and release parts of musical sounds. This approach is an extension of a spectral synthesis model we developed: the Reduced Parameter Synthesis Model (RPSM). The attack and release model is independent from a preceding spectral analysis as it is based on the time domain sustain part of the sound. The model has been tested with linear and polynomial shaping functions and produces good results for three different instruments. The time-domain approach overcomes the problem of synthesis artifacts that often occur when using spectral analysis/synthesis methods for sounds with transient events. Moreover, the model can be combined with any synthesis model of the sustain part and offers the possibility to determine the duration of the attack and release parts of the sound.