With both types of modulation sidebands are generated and this results in a change in the harmonic content of the waveform. This means that there can be sudden changes in the direction of the waveform (in addition to it being sped-up/slowed-down) but without the potential jumps at the point of inversion that can occur with bipolar AM. In the case of TZFM it is not the amplitude that is inverted but the phase of the waveform: In the Learning Modular video Chris Meyer describes this inversion as the oscillator вЂrunning backwardsвЂ™ while in his Audulus demonstration talks of a reversal of the direction in which the waveform is being read. Both do this by inverting the waveform in question. One aspect that through-zero FM and bipolar AM modulations have in common is that they donвЂ™t freeze (or shut-off) output when the modulation signal falls below zero. Learning Modular has a nice post on Understanding the Differences Between Exponential, Linear, and Through-Zero FM, and from there I revisited Know your Nodes video on Comparing different types of FM. Following on my post on bipolar VCAs: Since there are some similarities between whatвЂ™s going on with bipolar amplitude modulation and through-zero frequency modulation I thought IвЂ™d take another look at these topics in a little more detail.

Audulus muffwiggler