Master Volume Recalibration

1. Press the Master key.
2. Press the Utilities function key (F1).
3. Press the Recal… function key (F4).
4. Adjust the volume knob to the minimum position, then press OK.
5. Move the control to the maximum position, then press OK.
6. Press OK to store values in Flash RAM.

Source: Emulator IV — e-mu-emulator-iv-manual (manual)