The Monte Carlo program ISIDE, which simulates the operation of any semiconductor detector with associated electronics, has been recently improved and applied to the well-known material CdTe. The program has been used for investigating the influence of various parameters, such as bias voltage, polarity, time constants, etc. on the spectra obtained with low energy sources, in particular with 57Co. Electronic noise has been generally neglected in order to study, for instance, peak tailing in some detail. Some spectra are presented, however, which can be successfully compared with experimental ones by considering a reasonable electronic noise. Some considerations are given particularly concerning the effect of time constants on energy resolution at low gamma energies.