Good shout. That sounds roughly like a pre-emphasis filter, as is commonly used in mobile radio applications. Rolloff for those on the bottom end is usually ar

Good shout. That sounds roughly like a pre-emphasis filter, as is commonly used in mobile radio applications. Rolloff for those on the bottom end is usually around 300Hz (the CTCSS block filter), and around 3kHz (channel bandwidth limit) on the top end. Often those filters were implemented as analog designs, so a FIR with -10dB/dec rolloff would be closer to real-life. An FFT filter can be configured to act like a brickwall, which will sound subtly different.