For example normally the passband passes frequencies that allow you to listen to 500 through 3000 Hz. So this example would effectively narrow the frequencies to 1500 through 3000 Hz. IF shift normally doesn't show the frequencies. Other radios may actually change the width of the filter with similar listening results. Passband tuning and IF shift filters normally narrow the passband from one side only, eliminating either some of the high frequencies or some of the low frequencies.
Some radios allow selection of narrower passband filters.
Narrow filters are often 2000 Hz or 500 Hz wide. These filters are often only available when the TNC is wired to the radio's FSK jack and the radio's Rtty mode is selected. Modern filters often use DSP technology. While the passband tuning, IF shift, and narrow filters work on the signal before it enters the audio stages of the radio, the audio filters work on the signal after it has passed through the radio's audio circuits. Efficient use of spectrum.