The Model 129’s compact size, rugged construction, and simple controls made it a popular choice among musicians and audio professionals alike. The MXR Model 129’s pitch transposition was achieved using a voltage-controlled oscillator, which could be adjusted using a control knob on the front panel of the unit.
The MXR Model 129 Pitch Transposer was particularly well-suited for use in the studio, where it was used to create harmonies and other effects. It was also popular among guitarists, who used it to create a range of different sounds, from subtle pitch bends to extreme transpositions. Despite being produced in the late 1970s, the Model 129 remains a popular piece of equipment among musicians and audio enthusiasts today, and its simple yet effective design has made it a classic piece of audio equipment.