Before I talk about filters, let me quickly introduce you to the concept of the frequency spectrum.

As I’ve written before, sound that we can hear consists of a mix of lots of frequencies, ranging from the low boomy and bassy frequencies to the high shrill and airy treble frequencies.

 It’s standard convention to show these frequencies as a graph, like this.

The bass frequencies are to the left, and the treble frequencies are to the right.

Why is it that way? Well… they have no relation to the placement of those frequencies in a sound. They are this way because the frequency spectrum is actually a graph. The x-axis denotes the frequencies, and the vertical y-axis the volume of each frequency. And as with any graph, the numbering starts from lesser numbers, increasing upwards.

If you’ve used the equalizer on your stereo, you’ve already worked with the frequency spectrum.

This is how the very common V curve setting looks like.

What this is doing is boosting the volume of the low and high frequencies and reducing the volume of the middle frequencies. Wherever the line is above middle, it’s boosting the frequency by that much. Where it’s below middle, it’s cutting the frequency. Where the line is in the middle, those frequencies are unaffected.

Look at the curve below. What’s happening here?

As you can see, the higher frequencies are being cut, but the others are unaffected. Notice the amount of cut. It’s not a slight dip in the curve like the V shape in the previous example. It’s actually a complete removal of frequencies beyond a particular point to the right. So, there is actual filtering action happening here. The technical term for this is high-cut (because it is cutting the higher frequencies), and it also called low-pass (because it is allowing the frequencies on lower side of the curve to pass).

Okay… how about this one?

This time, the lower frequencies are cut. This is called low-cut filtering or high-pass filtering.

Look at the curve below. This is actually doing both low-cut and high-cut. It allows just a narrow band of frequencies in the middle to pass through. This is thus called band-pass filtering.

Okay. Enough theory for now. Let’s open up Clearsynth and have a look at the filter panel.

See the four buttons? Don’t they look familiar? 🙂

Yes, they are the low-pass, high-pass, band-pass and the V curve (the technical term for this one is notch filter).

But how do they sound like? Now that you know what they do, let’s hear them in action in my next post. Once you see the effect of these filters on the oscillator’s sound, the filter concept will become clear to understand.


6 Responses to “Filters”

  1. 1 agf
    December 29, 2009 at 9:07 pm

    Great tuturials for now keep the good work.

    Many thanks.

  2. 3 Thiago Sobral
    December 30, 2009 at 3:57 am

    This will be my new classroom now. This will be my opportunity to learn about synth.
    Please keep the good work!

  3. 4 Richard
    January 9, 2010 at 9:38 pm

    Great work!

  4. 5 liam west
    January 28, 2010 at 1:04 am

    this is brilliant, in the 1 and a half years of looking at websites and guides etc. i have found the most simplistic and natural feeling approach towards synth, i will certainly be showing other people of your work thank you so vey much.

  5. 6 Jay
    April 28, 2010 at 12:37 pm

    This is the most straight forward, easy to follow approach to synthesis I have read anywhere, web or books, very enjoyable to follow …..really excellent stuff – thankyou

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