It's short for tracking level D.

Class d is to change the audio signal into PWM, so that the whole circuit of the power amplifier works in the switch state. Achieve high efficiency and energy saving. However, some columns of audio signals are distorted and cannot meet the needs of high fidelity.

Tracking class D converts the power supply into PWM to realize voltage supply similar to the input audio signal waveform. Ensure that the audio loop is still in a pure analog state.

At the same time meet the requirements of high efficiency and high fidelity.

Class H is generally set with positive and negative voltages. It can be approximately understood as an automatic car with two forward gears, which has a large shift impact and unstable work.

Tracking class D is equivalent to CVVT CVT.