ARP 2500 module 1047 Multimode filter |
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This module is a combination low-pass, high-pass, band-pass
and notch-pass filter. The filter is capable of providing a wide variety
of formant shaping and tonal modulation. The band-pass response is
that of a natural acoustic resonator, and is most useful in synthesizing
instrument timbres.
The center frequency of the band-pass output is the cutoff frequency of the high-pass and low-pass outputs and is referred to as Fc. Fc is determined by the sum of the external control signals and the front panel "Coarse" and "Fine" adjustments. The response to the unattenuated control signals is 1 volt per octave. Fc is variable from 16Hz to 16KHz. With the "Resonance (Q)" knob at minimum, the band-pass output has a gain of 0.5 at Fc and attenuates 6dB per octave above and below Fc. The high-pass and low-pass outputs attenuate at 12dB per octave beyond the cutoff frequency. The notch output has a flat response everywere except for a deep 40dB notch. The notch frequency can be moved two octave to either side of Fc. As the "Resonance (Q)" control is turned up or an external control voltage applied to the "Q" inputs, a resonant peak occurs in all outputs except the notch. The bandwidth of this peak is equal to Fc/Q. Thus as the Q is varied from its minimum of 1/2 to its maximum of 512 the bandwidth varies from 2 octaves to 1/32 of a semitone. The "Keyboard Percussion" feature permits the filter to be used as a tone source or resonator. By applying a keyboard trigger pulse to the audio input, decaying sinusoids are produced at the band-pass, high-pass and low-pass outputs. (The module however, is prone to overloading, hence the inclusion of a helpful indicator lamp!) |
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