An exponential signal refers to a control voltage (CV) or modulation signal that has an exponential relationship with the parameter it controls. This means that as the voltage increases, the effect of the control signal on the parameter it modulates increases exponentially, rather than linearly.
Exponential signals are particularly relevant in the context of frequency control and pitch modulation for oscillators. Our perception of pitch is logarithmic, meaning that an octave increase in pitch corresponds to a doubling of frequency. Therefore, using an exponential signal to control the frequency of an oscillator results in a more natural and musically useful response, as it aligns better with our perception of pitch changes.
Some modules, like envelope generators or LFOs, may offer an option to switch between linear and exponential response curves. Additionally, modules like exponential converters or voltage-controlled amplifiers (VCAs) with an exponential response curve can be used to convert a linear signal into an exponential one.