12
Mar
10

From How and What to When and Why – Part 2

In Part 1, we discussed about oscillators, what characteristic sounds they have, and what to select when making different sounds. In this tutorial and the next, we’ll focus on filters and volume envelopes. Both of these are fairly straightforward, and if you’ve been following along, you should have already tried out different settings for the filter and volume envelopes.

Let’s start with filters. You must know the concept by now. Generally, you’d use a high pass filter to cut out low frequencies, and increase the brightness of the sound. And low pass filters to cut out the high frequencies, to make the sound duller or bass-heavy. As long as you know this basic idea, you are well set to use filters. You’ll obviously know what type of filter to set depending on how you want the sound to be modified. And the cutoff frequency is usually adjusted by sweeping through gradually, till the sound is just right. After that, you can add resonance to taste depending on what it does to the sound at the cutoff frequency you’ve set.

All these are very dependent on the sound you are trying to make, so it’s hard to give you any rules or guidelines to follow. However, since the usage is obvious, no rules are necessary. But there are a couple of special applications of filter that you should know.

As a mixing utility

When a mixing engineer mixes a song, it is common practice to filter out some low-end from each of the tracks. The reason for this is:

a. We do not have the equipment to both reproduce (speakers) or hear (our ears) such low frequencies.
b. Having a lot of unnecessary low frequencies have the effect of “muddying” up a song.

For a song in the mixing stage, if the individual instruments have to sound clearly, there shouldn’t be any frequencies in there that isn’t required and that makes no difference to the perception of sound. High and low pass filters do a good job of elimination such unwanted frequencies from both ends. If you are making a screaming synth lead patch, there is no need of low frequencies in the sound. But some of them might come up, especially if you use an oscillator waveform that has lot of harmonics (like saw). So, it’s a good idea to high-pass the sound with a suitable cutoff (One that does not take essential frequencies away and change the sound). Just make sure you use the keyboard track feature on your synth, so that the cutoff is uniform across notes.

To add interest to the sound

We already discussed filter sweeps in the filter tutorial. The idea is to have a small amount of resonance, and to change the cutoff frequency while the sound is playing. This leads to different movements of sound.

If you sweep a low pass or high pass filter, you can get a sound that starts off too dull or too bright, but then adds on frequencies to finally get to the original sound.

If you sweep a band pass, you get different types of sound ranging from dull (when cutoff is in the low-end) to telephone like sound (when cutoff is in the middle) to sharp shrill sounds (when cutoff is in the high-end).

These effects are usually achieved by automating the cutoff frequency on your DAW. Consult your DAW manual on how to automate plugin parameters on your DAW’s track.

Note 1: I still haven’t talked about band-cut or notch filters. One way you can use them is to remove particular frequencies in your sound that you don’t need. Automating them is also possible, but the effect is not as dramatic as the other filters, and could almost go un-noticed in a busy mix. There are times when it comes to good use. We’ll see that soon.

Note 2: Be careful about the resonance knob. When you set a resonance value, what you ask the synth to do is to boost the cutoff frequency by that much, irrespective of how loud the frequency already is. If the sound from the oscillators already have predominance in that frequency, the resonance can easily over-boost, resulting in extremely loud sounds, and may even damage equipment (your speakers or ears!). So, avoid setting extreme values. Resonance is anyway to be used just like a sprinkling of salt. Too much of it rarely sounds good.

Okay… on to part 3. We’ll next learn what volume envelopes to use when.

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