Module 1047 is a functional circuit package designed for use
in the ARP Series 2000 electronic music synthesizers. The
unit consists of a highly resonant filter with voltage controlled
frequency and resonance, and provides high pass, band pass,
low-pass, and notch outputs. 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 instrumental timbres. In
addition, the high degree of stable resonance and frequency
tracking accuracy attainable enables the filter to perform
precise, narrowband spectrum analysis of audio signals.
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 may be set by the frequency knob over
the range of 16 Hz to 16 KHz. Control signals applied to any
Fc input will change the center frequency from the knob setting
by 1 octave per volt when the knob above the control input
is at maximum. Control signals from the individual inputs
are summed with the Fc knob controls, and may be positive,
negative, or audio.
the RESONANCE (Q) knob at minimum and the RESONANCE switch
set to "NORM", the band-pass output has a gain of
0.5 at Fc and attenuates 6 db per octave above and below Fc.
The high pass output has unity gain from Fc to 20 KHz and
attenuates 12 db per octave below Fc. The low pass output
has unity gain from DC to Fc and attenuates 12 db per octave
above Fc. The notch output has flat response everywhere except
for a deep (40 db) notch at a frequency determined by the
NOTCH FREQ knob with this knob set to 1, the notch occurs
at Fc. NOTE: The notch output is effective only at low Q.
the RESONANCE (Q) knob is turned up, a resonant peak occurs
at Fc in all four outputs, except in the notch output when
the notch frequency is at Fc. The gain at this peak is numerically
equal to the "Q",and the 3 db bandwidth of this
peak is equal to Fc/Q. Thus, as Q is varied from V2 to 512,
the bandwidth varies from 2 Fc (2 octaves) to Fc/512 (1/32
of a semitone). When using high resonance, the audio input
control may have to be turned down to prevent overload. The
Q may be controlled by external signals. The Q control characteristic
is exponential; that is, each volt applied to a "Q"
input doubles the Q when the input knob is at maximum.
Some things not included in
the 1047E compared to the original 1047:
The keyboard percussion - can
be easily reproduced on the 1047E by feeding a pulse such
as an ADSR (with all controls set to zero) into the audio
input to "ping" the filter. The highly resonant
circuit generates a sine wave that decays at the rate determined
by the Q setting.
The final Q - is almost always
used along with the keyboard percussion. It's function can
also be easily realized on the 1047E by modulating the voltage
controlled resonance input by a keyboard gate or an ADSR.
When the key is released the resonance drops to the "final
Q". There was really no critical need to have any of
this, if you know how to patch the module correctly. These
2 features are in reality, just patching conveniences.
The limited resonance - is a
weak sounding version of the normal resonance, same sound,
just at really low volumes, sounds quite bad, so we intentionally
left that out.
We really wanted to have the
overload light, but there was no freaking room left!