Auto-Tune is a pitch-correction tool. It was originally developed by software company Antares for correcting minor tuning problems, meaning a singer didn't need to rerecord an otherwise good performance because of a solitary bum-note. However, when Cher's "Believe" came out in 1999, Auto-Tune made its mark as a creative tool. The dramatic and artificial sounding pitch adjustments achieved with Auto-tune have become a prominent production feature in contemporary pop music. By selecting "Baritone" or "Bass" in the "Input Type" tab on the Auto-Tune interface, you can set the tool to move all of your vocal into a lower register.
This is a similar effect to Auto-Tune, but it lacks the characteristically artificial feel. Rather than automating the correction, you set a degree by which you want to shift the pitch. Each note you sing subsequently is shifted by the pre-determined amount. Alternatively, you can adjust each note manually by selecting the note and inputting a new destination pitch.
Rather than dealing with pitch, equalization deals with frequency. By enhancing the lower frequencies in the voice, equalization can give your voice a deeper resonance. Everyone has a different tone to their voice; a natural bass baritone will sound deeper, even if he sings the same melody as a tenor. Equalization lets you bring out those deeper frequencies to add body to your voice.
Compression deals with dynamics. By cutting the volume peaks, it tempers the dynamic range of the audio and lets you boost the base level of the volume higher. If your natural vocal range doesn't permit you to sing powerfully in a low register, your voice will sound weaker when you sing low notes. Compression lets you boost the volume of the lower notes to the same volume as the more powerfully delivered high notes.
Reverb enhances the ambiance of a sound. It is similar to an echo, but distinct in that there is no repetition of sound, just persistence of the resonance. By adding reverb, you make a voice sound larger and more powerful. The reverb teases out the natural qualities of the voice and expands them. However, there needs to be a deepness to the voice initially for reverb to increase it.
Because humming doesn't require the same projection as singing, you can achieve a lower pitch. This trains the throat muscles to relax, enabling your voice to hit a lower pitch.
Your posture influences the amount of air that can pass from your diaphragm out of your mouth. Raise your chin and relax your shoulders to enable more air to pass during vocal projection. The more air you can force outward, the more power you have to project lower notes.