12.25

DR. OCTO REX LOOP PLAYER713
D Activate or deactivate the filter completely by clicking the Filter On button.
The filter is active when the button is lit.
Mode
With this selector you can set the filter to operate as one of five different types of filter. These are as follows:
•Notch
A notch filter (or band reject filter) could be described as the opposite of a bandpass filter. It cuts off frequencies
in a narrow midrange band, letting the frequencies below and above through.
• High-Pass (HP12)
A highpass filter is the opposite of a lowpass filter, cutting out lower frequencies and letting high frequencies pass.
The HP filter slope has a 12 dB/Octave roll-off.
• Bandpass (BP 12)
A bandpass filter cuts both high and low frequencies, while midrange frequencies are not affected. Each slope in
this filter type has a 12 dB/Octave roll-off.
• 12 dB Lowpass (LP 12)
This type of lowpass filter is also widely used in classic analog synthesizers (Oberheim, early Korg synths, etc.). It
has a gentler slope (12 dB/Octave), leaving more of the harmonics in the filtered sound compared to the LP 24 fil-
ter.
• 24 dB Lowpass (LP 24)
Lowpass filters lets low frequencies pass and cuts out the high frequencies. This filter type has a fairly steep roll-
off curve (24dB/Octave). Many classic synthesizers (Minimoog/Prophet 5 etc.) used this filter type.
Filter Frequency
The Filter Frequency parameter (often referred to as “cutoff”) determines which area of the frequency spectrum the
filter will operate in. For a lowpass filter, the frequency parameter could be described as governing the “opening” and
“closing” of the filter. If the Filter Freq is set to zero, none or only the very lowest frequencies are heard, if set to max-
imum, all frequencies in the waveform are heard. Gradually changing the Filter Frequency produces the classic syn-
thesizer filter “sweep” sound.
! Note that the Filter Frequency parameter is usually controlled by the Filter Envelope (see “Filter Envelope”) as
well. Changing the Filter Frequency with the Freq slider may therefore not produce the expected result.
Resonance
The filter resonance parameter affects the character of the filter sound. For lowpass filters, raising the resonance will
emphasize the frequencies around the set filter frequency. This produces a generally thinner sound, but with a
sharper, more pronounced filter frequency “sweep”. The higher the resonance value, the more resonant the sound be-
comes until it produces a whistling or ringing sound. If you set a high value for the resonance parameter and then vary
the filter frequency, this will produce a very distinct sweep, with the ringing sound being very evident at certain fre-
quencies.
• For the highpass filter, the resonance parameter operates just like for the lowpass filters.
• When you use the Bandpass or Notch filter, the resonance setting adjusts the width of the band.
When you raise the resonance, the band where frequencies are let through (Bandpass), or cut (Notch) will become
narrower. Generally, the Notch filter produces more musical results using low resonance settings.