The FX-25 is a forgotten cousin of the popular DOD 440 envelope filter. It is a righteous envelope filter with a good amount of quack. The advantage of the FX-25 is that it uses less expensive parts compared to the 440. The 2022 version has no circuit changes from the 2019 version.
The FX-25 has three controls:

1. SENSE: This control adjusts the overall sensitivity of the envelope detector. It can be adjusted from least to greatest sensitivity.

2. RANGE: This control adjusts the resonant peak of the swept filter. It can be adjusted from low to high.

3. BP/LP: This switch allows you to select between low-pass and band-pass filtering. The low-pass option is on the left side of the switch, while the band-pass option is on the right side.

Overall, the FX-25 is a versatile envelope filter that offers a range of filtering options. It is a cost-effective alternative to the DOD 440 and has been used by musicians like Flea.

Summary created by AI from the original source.