Any moving average is an oscillator, and a bandpass filter can be generated by combining low-pass and high-pass filters. Converting a low-pass filter to a bandpass filter is more practical, while converting a high-pass filter to a bandpass filter may not be as practical. The conversion process is irreversible. John F. Ehlers has developed many technical indicators based on digital signal processing, including low-pass, high-pass, and bandpass filters.
This article introduces the common types of filters used in technical analysis, including low-pass filters, high-pass filters, band-pass filters, and notch filters. Although pure notch filters are not commonly seen in technical indicators, some indicators, such as the high-low difference, can be approximately considered as having notch characteristics. Additionally, the article lists some common technical indicators and explains their relationship with filters.