A bitcrusher is basically another form of distortion. This reduces the sample rate or the resolution (bit rate) of the audio. When you lower the sampling rate, high-frequency information is lost and the waveform becomes much coarser. Reducing the sampling rate drastically results in a very metallic sound.
If you reduce the resolution of the audio material, the waveform becomes step-shaped, because the information about amplitude curves is lost. Reducing the bit count to a minimum results in a crackling sound, as the waveform only jumps between very coarse levels and no uniform progression can be mapped.
A chorus is a stereo effect that duplicates a given signal and delays it in time or phase by about 15 ms. This short time interval means that the signals are not perceived as separate sound events - ie as echoes - and that a sound in the stereo base is broadened. Incidentally, the delay time is modulated, that is slightly varied, resulting in a pitch difference. A chorus is suitable for expanding the stereo image of a sound.
In addition to the reverb, a delay is a further processing that has an effect on the spatial sensation. Similar to the effects already mentioned, there are also delayed delays of a signal, the time interval being so high that the sound sources are perceived separately from one another. One form of delay is e.g. an echo. A stereo effect of a delay arises from the fact that time-delayed signals are distributed in the panorama.
Similar to the Chorus, the Flanger also works with a duplicate of the signal, with the delay times being shorter and leading to a comb filter effect with spacey character via feedback of the effect signal. Here, the sound intervention is slightly stronger than the chorus. Flange effects can therefore not only lead to the processing of the stereo impression, but at the same time be used via an automation for slight variations in the song.
The phaser effect is based on the flanger, but works with more complex comb filter effects, resulting in a different sound. The copy of the input signal is passed through a series of all-pass filters that result in a variation of time delays.
To add artificial spatial information to a signal, a reverb is usually used. This reverb generates reflections and simulates a room in which the corresponding signal is heard. The room characteristic or the reverberation time can be changed via corresponding parameters. Since the human ear is used to such spatial information, an effect leads to a perceived naturalness.
In summary, the three effects mentioned are distortions that vary from subtle overdrive intervention to an extreme sonic result of the fuzz. The respective distortions result in additional harmonics being added to the output signal.