Prerequisites: understanding of basic mixing techniques, relationship between frequency in Hertz and notes in a scale, fundamental frequencies, etc.
Filters are recording and mixing tools that adjust the volume of specified frequencies in a specified manner. They are found in many different places; mixing consoles, microphones, and preamplifiers are just a few examples in terms of recording audio. However, filters are also found in many consumer electronics devices.
Filters work by cutting a specified frequency range at a (usually) predetermined rate. For example, most High Pass Filters will have a degree of attenuation of about 3 dB per octave all the way down the frequency spectrum. The point where attenuation begins is called the Cutoff. More often than not, the Cutoff frequency itself will often be attenuated slightly, as well as the frequencies above or below it.
 Types of Filters and Examples of use
- High Pass - High Pass Filters will filter out frequencies below a specified cutoff frequency and allow the high frequencies to pass through. High Pass Filters are often used on vocals at around 100 Hz to cut out unnecessary low end from the voice, remove air conditioner noise, and provide more clarity.
- Low Pass - Low Pass Filters are the reverse of High Pass Filters and will filter out frequencies above a specified cutoff frequency while allowing the lower frequencies to pass through. Low Pass Filters are often used to remove hiss and noise from tracks.
- High Cut - High Cut Filters are similar to Low Pass Filters. The difference is that High Cut Filters have a much sharper degree of attenuation, and can sound harsher.
- Low Cut - Low Cut Filters are similar to High Pass Filters. Again, the difference is that Low Cut Filters have a much sharper degree of attenuation, and can sound harsher.
- Band Pass - Band Pass Filters combine High Pass Filters and Low Pass Filters to allow a specified range in the middle of two selected frequencies to be boosted or cut. This can be used to create a "Megaphone" effect on a vocal track. "Loudness" buttons also act as Band Pass Filters.