011 – filters – one of three

In the next few blog posts, I will briefly explain and offer some use case examples for a selection of tools and techniques which I find to be rather misunderstood. These tools will also combine together nicely, so in a few weeks’ time, you’ll have a better understanding of where to go with some of your creative and mixing decisions.

This week we will begin with filters, and next week I’ll finish on that theme by running through equalisers.

Filters are incredibly simple at first, and equally, incredibly important. As with all effects, they can be used both creatively and technically; correct use will not only clean up your mixes but can also add much more depth and interest. Filters usually come in four primary types and a few other flavours which are combinations of the four basic ones. A low pass filter is used to remove higher frequency content, thus the name; the lows pass. Conversely, there is also the high pass, which cuts out low frequencies. The next two can be viewed as combinations already, a notch filter allows all frequencies to pass except for a specified band; the notch. A band pass is the opposite, and will only allow a specified frequency band through. Your standard filter will have a few basic settings, filter type, cutoff frequency, resonance, and slope. More controls can be added when the filter is more advanced or designed for different purposes.

How do I decide which filter to use and where? As with any effect, the first thing to ask is, what would I like to do? It seems completely obvious, but it is completely common for many people to throw on a filter or eq, and a compressor, onto every channel – either because they can or someone told them that was a good idea. Some tracks and styles may need all that, sure, but most don’t. So start by deciding what you want to do, and if a filter helps you get there, we can move on. If it’s a simple cut of offending or muddying frequencies, we can simply make that cut, but we don’t have to stop there. Filters have always been used as creative tools as well as precise technical tools. For my ears, this means using specific analogue-modelled filters to achieve a certain colour or distortion to the sound. Clean digital filters are fantastic for clean adjustments to sounds, but analogue-modelled plugins (or better yet, the real thing, if you can afford it) can add that last little bit to bring a sound out of the mix or give it a little something extra. The classic example of this is the classic Moog filter. Depending on the model and derivation of the particular plugins you have available, the two key parameters for such colouration are the resonance, that is the emphasis placed on the cutoff frequency, and the filter drive if available. The character of the sound will change with modifications to these parameters and will depend on the analogue model used. As an easy way to play around with the different modelling types, Live’s built-in auto filter device uses a few, which are also available in the filter sections of the operator, simpler, and sampler midi instruments. Ableton themselves are a little skittish about saying exactly which filters they modelled, which include the famous ms-20 and moog designs.

As a final note, I will briefly cover some of the inherent issues with filters. They cannot cut absolutely surgically, for example, a sound cannot be at 0dB at 400Hz, and cut to -∞dB at 410Hz. Filters need some space to cut, and that is called the slope. Slopes generally range from -6dB per octave to -48dB/oct. The steeper you go, the more phasing issues can occur, as the wave phase at the cut frequency range is affected by the filter. For this reason, cutting too steeply, with too many consecutive filters, or at very low frequencies can be very detrimental to sound quality. In most cases, it is not a huge issue, but something to be aware of.

Next week we will continue on this theme with how equalisers work and how to best use them.

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