| A filter allows you to remove unwanted frequencies | | | | can give the vocals more brightness and you can also |
| and also allows you to boost certain frequencies. | | | | use it on any recordings that have a low frequency |
| Which frequencies are removed and which | | | | hum or sound that is dirtying the sound, although, in this |
| frequencies are left depends on the type of filter you | | | | instance it would be a limited tool, as you could also cut |
| use. | | | | out the lower frequencies in the sound itself, but still a |
| Before we can list the different types of filters and | | | | tool that has many uses. |
| what they do, there are a few terms and definitions | | | | Band Pass-BPF |
| we need to cover. These are crucial and are used all | | | | This is a great filter. It attenuates frequencies below |
| the time so it is important that you know what these | | | | and above the cut-off and leaves the frequencies at |
| terms are and what they mean. | | | | the cut-off. It is, in effect, a low pass and a high pass |
| Cut-off frequency This is the point (frequency) at | | | | together. The cool thing about this filter is that you can |
| which the filter begins to filter (block or cut out). The | | | | eliminate the lower and higher frequencies and be left |
| filter will lower the volume of the frequencies above or | | | | with a band of frequencies that you can then use as |
| below the cut-off frequency depending on the type of | | | | either an effect, as in having that real mid range type |
| filter used. This 'lowering of the volume of the | | | | of old radio sound, or use it for isolating a narrow band |
| frequencies,' is called Attenuation. In the case of a low | | | | of frequencies in recordings that have too much low |
| pass filter, the frequencies above the cut off are | | | | and high end. Sure, it's now really made for that but the |
| attenuated. In the case of a high pass filter, the | | | | whole point of synthesis is to use tools because that's |
| frequencies below the cut off are attenuated. Put | | | | what they are, tools. Breaking rules is what real |
| simply: in the case of a low pass filter, we are trying to | | | | synthesis is all about. Try this filter on synthesizer |
| block the (higher) frequencies above a certain point | | | | sounds and you will come up with some wacky |
| and allow the lower frequencies through. In the case of | | | | sounds. It really is a useful filter and if you can run |
| a high pass filter, the opposite is true. We try to cut out | | | | more than one at a time, and select different cut-offs |
| or block frequencies below a certain point and allow | | | | for each one, then you will get even more interesting |
| the higher frequencies through. On analogue | | | | results. |
| synthesizers this cut-off was called the slope or | | | | Interestingly enough, band pass filtering is used on |
| gradient. The actual terminology was more accurately | | | | formant filters that you find on so many softsynths, |
| described as the RC (resistor/capacitor). Don't worry | | | | plugins, synthesizers and samplers. Emu are known for |
| about this for now. What you do need to know is that | | | | some of their format filters and the technology is |
| on analogue synthesizers, the filter behaves differently | | | | based around band pass filters. It is also good for |
| to modern synthesizers that use algorithms. | | | | thinning out sounds and can be used on percussive |
| Analogues use circuitry and for that reason alone, it | | | | sounds as well as creating effects type of sounds. I |
| takes time for the filter to attenuate frequencies, in | | | | often get emails from programmers wanting to know |
| proportion to the distance from the cut-off point. | | | | how they can get that old radio effect or telephone |
| Today's technology allows for instant cut-off as the | | | | line chat effect or even NASA space dialogue from |
| filter attenuation is determined by algorithms as | | | | space to Houston. Well, this is one of the tools. Use it |
| opposed to circuits. That is why the filters off an Arp | | | | and experiment. You will enjoy this one. |
| or Oscar etc, are so much more expressive and | | | | Band Reject Filter-BRF-also known as Notch |
| warm as they rely completely on the resistors and | | | | This is the exact opposite of the band pass filter. It |
| capacitors to, first warm up, then to work but in a | | | | allows frequencies below and above the cut-off and |
| gradual mode(gradual meaning sloped or curved as | | | | attenuates the frequencies around the cut-off point. |
| opposed to instant). Depending on how well a filter | | | | Why is this good? Well, it eliminates a narrow band of |
| attenuates or the way it attenuates gives us an idea | | | | frequencies, the frequencies around the cut-off, so, |
| of the type of sound we will achieve with an analogue | | | | that in itself is a great tool. You can use this on all |
| filter. You often hear someone say 'That Roland is | | | | sounds and can have a distinct effect on a sound, not |
| warm man' or 'Man, is that Arp punchy'. These are | | | | only in terms of eliminating the frequencies that you |
| statements that explain how a Roland's filters sound or | | | | want eliminated, but also in terms of creating a new |
| how potent the Arp's filters are. So, the speed at | | | | flavour to a sound. But its real potency is in eliminating |
| which the filter attenuates is called the slope or | | | | frequencies you don't want. Because you select the |
| gradient. Another point to raise now is that you will | | | | cut-off point, in essence, you are selecting the |
| often see values on the filter knobs on analogue | | | | frequencies around that cut-off point and eliminating |
| synthesizers that have 12dB or 24dB per octave. That | | | | them. An invaluable tool when you want to hone in on |
| basically means that each time the frequency doubles, | | | | a band of frequencies located, for example, right in the |
| the filter attenuates by 12dB or 24dB everything at | | | | middle of a sound or recording. I sometimes use a |
| that frequency. These are also known as 2 pole or 4 | | | | notch filter on drum sounds that have a muddy or |
| pole filters (fig 2), each pole represents 6dB of | | | | heavy mid section, or on sounds that have a little noise |
| attenuation. This is how analogue circuits were built, the | | | | or frequency clash in the mid section of a sound. |
| number of circuits being used by the filter to perform | | | | Comb |
| the task at hand. | | | | The comb filter is quite a special filter. It derives its |
| Although this is a general belief, it is one that is not | | | | name from the fact that it has a number of notches at |
| entirely accurate and we will come to that later, as this | | | | certain distances (delays), so it looks like a comb. The |
| is tied into the topic of roll-off. I do not expect you to | | | | Comb filter differs from the other filter types, because |
| understand the concept of 2 or 4 pole at this stage. I | | | | it doesn't actually attenuate any part of the signal, but |
| am just throwing it in for tagging purposes. Since the | | | | instead adds a delayed version of the input signal to |
| term has been mentioned, it will stay in your mind and | | | | the output, basically a very short delay that can be |
| when we come to tackle this area, you will say 'Yeah, | | | | controlled in length and feedback. These delays are so |
| I remember the dude saying something about that'. The | | | | short that you only hear the effect rather than the |
| best way, and one that I always sign off with, is to | | | | delays themselves. The delay length is determined by |
| experiment. Sweep that filter. Sweep is another one of | | | | the cut-off. The feedback depth is controlled by the |
| these funky words we programmers or engineers use | | | | resonance. Don't worry about resonance for now as |
| and all it really means is grab the filter knob and twist it. | | | | we will cover this extensively in the next installment of |
| Yes, I know, we like to be a bit flash, but it sounds | | | | these ongoing tutorials. |
| cool.... | | | | This filter is used to create a number of different |
| If you delve into the filters that Emu provide on their | | | | types of effects, chorus and flange being two of the |
| synthesis engines, then it could go into pages, if I had to | | | | regulars. But the comb filter is more than that. It can be |
| list them all. | | | | used to create some incredible dynamic textures to an |
| But for now I am keeping it simple and listing the | | | | existing sound. When we talk of combs, we have to |
| standard filter types and what they do. | | | | mention the Waldorf synthesizers. They have some of |
| Low Pass-LPF | | | | the best comb filters and the sounds they affect are |
| As mentioned earlier, this filter attenuates the | | | | so distinct, great for that funky metallic effect or |
| frequencies above the cut-off point and lets the | | | | sizzling bright textures. |
| frequencies below the cut-off point through. In other | | | | Parametric |
| words, it allows the lower frequencies through and | | | | This is also called the swept eq. This filter controls |
| blocks the higher frequencies, below and above the | | | | three parameters, frequency, bandwidth and gain. You |
| cut-off (the frequency at which the filter begins to kick | | | | select the range of frequencies you want to boost or |
| in). The low pass filter is one mutha of a filter. If you | | | | cut, you select the width of that range and use the |
| use it on a bass sound, it can give it more bottom and | | | | gain to boost or cut the frequencies, within the |
| deep tones. If used on a pad sound, you can have the | | | | selected bandwidth, by a selected amount. The |
| filter open and close or just sweep it and it gives that | | | | frequencies not in the bandwidth are not altered. If you |
| nice closing and opening effect. You can also use this | | | | widen the bandwidth to the limit of the upper and |
| filter cleverly by removing higher frequency sounds or | | | | lower frequencies ranges then this is called shelving. |
| noise that you don't want in your sound or mix. | | | | Most parametric filters have shelving parameters. |
| Because it blocks out higher frequencies at the cut off | | | | Parametric filters are great for more complex filtering |
| you set, then it's a great tool if you want to remove | | | | jobs and can be used to create real dynamic effects |
| hiss from a noisy sample or, if you use it gently, you | | | | because they can attenuate or boost any range of |
| can remove tape or cassette hiss. | | | | frequencies. |
| High Pass-HPF | | | | Well, I hope this has helped to demystify the confusing |
| This is the opposite of the low pass filter. This filter | | | | world of filters for you and I suggest that you ignore |
| removes the frequencies below the cut-off and allows | | | | the filters on your synthesizers, be they hardware or |
| the frequencies above the cut-off through. Great for | | | | software, at your own peril, because they are truly |
| pad sounds, gives them some top end and generally | | | | powerful sound design functions. |
| brightens the sound. It's also really good on vocals as it | | | | |