rj_filter4 BETA ---------- This is an audio-range filter module with about 76 different low-pass filter configurations based on different arrangements of up to 5 filter stages, including many which model analog component variations, based on the Stilsen/Smith Moog design with Q compensation. It is an updated version of RJ_FILTER3 with * internal use of 64-bit floating point * various optimizations * additional high-pass filter versions on the Complex filters * negative frequency CV input protection guards against some pops * FM distortion for better emulation of transistor/diode ladder/chain/bridge filters The Input pin is the audio signal from the Oscillator or other well behaved signal. The filter has been designed to provide warm distortion early. (If the signal is not within the normal range, there may be clipping.) The Output pin is the filtered signal. The Frequency pin is the cutoff frequency of the filter. This more or less follows the 1V per 8ve rule for synthedit. (You may find it useful to use a clipper set, say, to 0V min and 11V maximum, if your synth configuration would cause such values) so that out-of-range variation to the frequency are not passed on to the filter: changes to the filter frequency are quite expensive for CPU.) The Resonance pin controls the resonance from 0 to 10. Typically self resonance will occur around 9V input, but each filter's response is different. The Type pin select high pass or low pass. Not every low pass filter has a high pass equivalent and some of the high-pass filters have odd responses: they are provided as a bonus: use your ears. The Poles pin selects the different number of filter stages used for filtering: the values are 2 (i.e. approx 12db/8ve cut) to 5 (i.e. approx 30db/8ve cut). The value "Complex" selects various asymmetrical band-pass configurations, for example 4 low pass stages and 1 high pass stage. Low numbers of filter stages do not resonate strongly; high numbers of filter stages can selef resonate. The QTap pin selects the number of stages at which the feedback circuit (used for resonance) is tapped at. The values are from 2 to 5. The Emulate pin selects either Digital emulation (simple distortion, and exact alignment of the frequency responses of each stage) or Analog emulation (multiple saturation with asymetrical and symetrical distortion, and small variations in the responses of each stage.) Analog emulation requires more CPU. The warmth/bite and tone of the filter will be different depending on whether the signal is overdriven or underdriven. The Bass-boost pin increases the output level as the cutoff frequency goes low. At mild settings this simulates a compression effect that might occur on some under-powered circuits. The FM Distortion pin selects various small levels or kinds of frequency modulation by the carrier wave. A vale of None selects no modulation. The three levels of "Chain" select different levels of frequency modulation: the cutoff frequency of the filter is modulated by the input (plus resonance) signal of the the filter. The three levels of "Ladder" select different levels of modulation: the cutoff frequency of the filter is modulated by the maximum (absolute) value of the raw input and the input+resonance, where both are of the same sign, or 0 where they differ. The FM Distortion pin is intended to simulate a postulated effect on diode/transistor ladder/chain/bridge filters where both the control current (as a DC signal) and the input current (as a small signal AC) are fed into diodes/transistors to provide a variable resistance for an RC filter: in this topology (as distinct from, say, a transconductance implementation) the input signal will also modulate the frequency to a small extent. This may be a subtle effect, most noticeable at high settings, with a large number of resonance stages, rich input waveform, high resonance and high input levels. The Zing pin adjusts how much resonance changes depending on the frequency pin from 5 to 15. 10v is typical for flat response, but each filter's response is different. For example, the famous minimoog filter has less resonance at lower frequencies. (Note that in general, the cutoff rate in db/8ve decreases as the frequency rises in this filter's design, and the Zing pin helps this kid of interesting variation.) This pin is probably not suitable for presentation to end-users. IMPORTANT NOTE: If you have a problem where the filter seems to keep awake too long, consider putting a VCA before the filter or using an rj_sleeper module. Available for unrestricted use. No warranty of quality or fitness for purpose made. No promise of maintenance. Please include an acknowledgement to me (Rick Jelliffe) in the GUI, docs or website, as appropriate (however this is not a condition of use, just politeness and so I can track usage). Copy it into Modules/MyModules