Specifications
16 
Filter 
Mopho x4 features a selectable 2- or 4-pole, low-pass filter per voice. 
4-Pole—Selects the filter configuration. When lighted, the filter is in 4-pole 
mode. A 4-pole, low-pass filter rolls off frequencies above the cutoff frequency 
at a slope of 24dB/octave. When the light is off, the filter is in 2-pole mode and 
has a slope of 12dB/octave and a more gradual rolloff of the higher frequencies. 
Frequency: 0...164—Sets the base filter cutoff frequency over a range of more 
than 13 octaves.  
Resonance: 0...127—Emphasizes a narrow band of frequencies around the 
cutoff frequency. In 4-pole mode, high levels of resonance can cause the filter to 
self oscillate. In 2-pole mode, resonance is much more subtle and self oscillation 
does not occur. 
Audio Mod: 0...127—Controls the amount of audio from oscillator 1 used to 
modulate the filter cutoff frequency. For filter-only audio, set the oscillator Mix 
to 127, oscillator 2 Shape to Off, and oscillator 1 Shape to the desired 
waveshape. This is useful for bell-like FM sounds. A wide range of sounds can 
also be made using A
UDIO MOD with the oscillators routed normally through the 
filter. 
Key Amount: 0...127—Sets the amount of modulation from the keyboard to the 
filter cutoff. A setting of 64 will step the filter in one semitone increments for 
each note, 32 would be quartertones, and so on. 










