Signal Processing

The MACD is a filtered measure of the velocity. The velocity has been passed through two first order linear low pass filters. The "signal line" is that resulting velocity, filtered again. The difference between those two, the histogram, is a measure of the acceleration, with all three filters applied. The "MACD crossing the signal line" suggests that the direction of the acceleration is changing. "MACD line crossing zero" suggests that the average velocity is changing direction.