Filters in action – Part 2

There’s a little bit more sound shaping you can do with filters. I will be explaining about resonance and the key track button in this  post.

You’ve seen how modifying the cutoff frequency can make changes the sound. What we were doing was adjust the position of the cutoff line horizontally. Now imagine what would happen if the line moved vertically? Look at the picture below.

I’ve explained before how if the line is above the middle, the frequency at that position will be boosted by that much. Here, the filter is actually making a high cut, but it is boosting the frequency just before the frequency that is being cut .

Try this on Clearsynth now. Sweep the cutoff to a saw wave downwards, and leave the cutoff knob somewhere in the middle. Gradually increase the value of the resonance knob. Don’t turn it to the max though. Leave it somewhere in the middle as well. Now do the cutoff knob sweep back upward. As you can hear, not only does the sound change, the sweep also sounds more pronounced this time. This is because the frequency point where the cutoff is happening is now emphasised. Actually, this is one of the uses of resonance. You can hear cutoff sweeps on synth lines in songs sometimes, with an increased resonance to emphasise the sweep. There are other uses of resonance that’ll be explained once we start the sound tutorials.

That leaves us with the last button, key track. Try this excercise. Select saw oscillator, set the cutoff knob to the middle and resonance to zero. Start playing notes from C4 upwards on your keyboard. Notice what happens as you reach C5. The higher notes sound different, and by the time you get to A5, you’ll not hear any sound at all. It’s almost as if you’ve modified the cutoff frequency gradually! Actually, the cutoff frequency hasn’t changed. The frequency of the input signal has! Lower notes have lower frequencies and higher notes have higher frequencies, remember?

Now we have a problem! What filter frequency do we set? Should we change the cutoff for every note that’s played. Yes, you should! But you don’t have to. Key track button does all that for you! If this button is selected, Clearsynth checks the frequency of the signal from the oscillators, and automatically adjusts the cutoff frequency so that the intended sound is retained. Turn the button on and repeat this excercise and you’ll hear exactly what’s going on.

Congrats! You’ve learnt quite a lot so far. In the next post, I’ll be explaining about using the second oscillator, and you’ll be able to use all the controls in the top half of the synth! Keep reading!


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