This is aimed specifically at the stock 1 Pole High Pass Filter. What it is and what it’s useful for.
What is the 1 Pole HPF useful for?
Although it doesn’t have a steep cut off slope, and has no feedback/resonance control, this filter still has it’s uses. The idea of this filter is that all frequencies below the cutoff (pitch) frequency are attenuated by 6dB for every octave below the cutoff frequency. If for any reason you need a steeper cutoff slope just combine two or more in series. The only settings of note are;
Frequency Scale (Properties): Set to either 1 V/Octave or 1V/kHz.
Pitch: The cutoff frequency. Below this frequency the audio is attenuated with a slope of 6 dB/Octave.
1 DC Blocking.
Some structures may, due to the way they work may generate a DC component in their output audio. An example of this could be a waveshaper. This is undesirable as it can cause all sorts of issues such as assymetric clipping.
If you have an audio signal output at +/-5 volts peak to peak, and you have a +3 volts DC component, your +ve peal voltage is going to be 8 volts rather than 5, and if a sudden increase in audio occurs then you’ll quickly hit the +10 volts maximum for audio, and run into harsh, digital clipping. In the example below you can see where I have used (albeit a rather extreme wavshaping shape) a waveshaper and there is a noticeable peak showing at 10 Hz, which on it’s own could cause some audio issues, but also if you look at the voltmeter on the signal out plug of the wavehsaper we have 2.061 volts DC, which is exactly what we want to avoid. At the output of the 1 pole HPF (which I set to 100 Hz) however the 10 Hz peak in the spectrum is gone along with some others being much reduced, and we also lose that 2.061 V DC component.
2 Effects such as Reverb.
Effects such as Reverb, Echo, Phasing and Chorus all sound much better if we apply a high pass filter to the audio input of the effect, it will sound much cleaner if a wide range of frequencies is being fed into the effect. Allowing lower bass (below 100- 200 Hz) frequencies into Reverb and Echo quickly makes the sound muddy, or even overpower the higher frequencies.
3 EQ and Mixing Plugins
There are several uses here, getting rid of low frequency rumbles, and hum which can quickly overwhelm a mix, or cause clipping. Use of High Pass filters on some instruments can also improve the clarity of a mix when used well.
Always include high pass filtering in any Mixer VST, Mixer Channel Strip VST etc.