RELATIVE Q FACTOR VST OCTAVE HOW TO

It should be a small leap to see that we can combine a low-pass filter and a high-pass filter to create another type of filter found on many synthesizers: the band-pass filter. Figure 6: An idealised RC band-pass filter. And, once again, the cutoff frequency is simply proportional to 1/R.įigure 5: A simple RC high-pass filter. As you can see, it has the same two components as the variable low-pass filter, but they are swapped around in the circuit. You can compare the different frequency responses of low-pass and high-pass filters in Figure 3 and Figure 4.įigure 5 shows the simplest high-pass filter with a variable cutoff frequency. This is a device that, instead of attenuating high frequencies, attenuates the low ones. The same is also true of a high-pass filter. But the principle remains the same: by adjusting the value of one or more components in a given filter circuit, you can adjust the cutoff frequency. Of course, this is an example of a passive filter, and almost every analogue synthesizer filter is active (ie. In this case, it's the filter cutoff knob (or slider). And what would a synthesist use to control the potentiometer that lets you do this.? Answer: a knob or a slider. Conversely, if you reduce the resistance, the cutoff frequency rises. In other words, if you increase the resistance, the cutoff frequency drops. Figure 4: The gain response of a 6dB/octave high-pass filter. The relationship is so simple that I can write it like this:įigure 3: The gain response of a 6dB/octave low-pass filter. Now, I have done my best to avoid any maths, but there's something you ought to know about this filter: the cutoff frequency is directly related to the amount of electrical resistance provided by the resistor, and the capacitance of the capacitor. We then get the circuit shown in Figure 2. Let's consider what happens if we replace the resistor at the top of the diagram with a variable resistor, more commonly known as a potentiometer. We'll start, as usual, with our simple 6dB/octave low-pass RC filter (see Figure 1). So let's introduce another handful of vitally important ideas, tie up a few loose ends, and bring ourselves to the point where we can, finally, get twiddling. No matter how you use them, you will eventually end up with something that sounds about as interesting as a documentary on last year's party political broadcasts. Figure 2: An RC low-pass filter with variable cutoff frequency.No! All the filters we've discussed so far have been static, acting just like tone controls, albeit rather powerful ones. Yes?įigure 1: A passive 6dB/octave RC low-pass filter. So now we can start talking about winding up the resonance to 11, overdriving the input and creating some classic tearing analogue filter sweeps. You will also be able to appreciate how that filter messes around with the phases of the harmonics within any signal you pass through it.

RELATIVE Q FACTOR VST OCTAVE HOW TO

If you have read the most recent two parts of this series you'll now know (at least in principle) how to construct a 24dB/octave filter and define its cutoff frequency. In this Part, he considers what happens when you make the design more sophisticated.

As Parts 4 & 5 of Gordon Reid's series showed, even the simplest analogue filters mess with your sound in complicated ways.

Relative q factor vst octave