!"#$%&'()*(+,-%&'.(

! "#$!

Chapter 7 – Filters

When we think of filters we think of equalisation and how the two are so easily

interchanged and linked to each other. If anything, this direct relationship has

led to a lot of confusion. I have covered the subject of equalisation in one of my

other books ‘Sound Equalisation Tips and Tricks’ so I do not want to explore how

equalisation works and where filters feature in its makeup. What I do want to

concentrate on is the synthesizer type of filter and how it has now become an

incredibly useful tool and one of my favourites sound manipulation tools. I will

cover the basic types of filters but will go into a great deal of detail when coming

to using them in working examples.

Let us briefly look at the terminology used and what they mean along with the

most basic filter types.

Cut-off frequency

This is the point (frequency) at which the filter begins to filter (block or cut out).

The filter will lower the volume of the frequencies above or below the cut-off

frequency depending on the type of filter used.

Attenuation

This ‘lowering of the volume of the frequencies,’ is called Attenuation. In the

case of a low-pass filter, the frequencies above the cut-off are attenuated. In the

case of a hi-pass filter, the frequencies below the cut-off are attenuated.

Resonance

Boosting the narrow band of frequencies at the cut-off point is called resonance.

Also known as Q and bandwidth, in effect, he higher the resonance, the

narrower the bandwidth.

!"#$%&'()*(+,-%&'.(

! "#$!

Q

Also known as ‘width of the filter response’, this is the ‘centre frequency’ of

the bandwidth and is measured in Hz. Also know as bandwidth and resonance.

A high Q value denotes a narrow filter width (bandwidth). A low Q value denotes

a wide filter width (bandwidth).

This is actually a very important piece of information because with the Q control

alone you can make your audio sound high and brittle or warm and musical. This

does not mean that you must use low Q values all the time, in the hope of

attaining warmth, but you must understand what frequencies need filtering. If

your intent is to use EQ as a musical tool, then be aware of what the Q value can

do to audio. For creative EQ, this is a weapon often ignored.

Slope

The rate at which a high or low frequency EQ section reduces the level above or

below the cut-off frequency is termed as the ‘Slope’ and the shape and

parameters are denoted as dB per octave and are usually: 6, 12, 18 or

24dB/octave. Slope also determines the characteristic of the filter and can range

from smooth to extreme (gentle to aggressive).

Pole

You will often come across the terms 2 pole or 4 pole. This refers to the number

of circuits filters used to attenuate the signal with each pole referring to a value

of 6db.

!"#$%&'()*(+,-%&'.(

! "#$!

Low pass filter

Hi pass filter

In the low-pass filter diagram the frequencies below the cut-off are allowed to

pass through whereas the frequencies above the cut-off are attenuated.

In the hi-pass filter diagram the frequencies below the cut-off are attenuated

and the frequencies above the cut-off are allowed to pass through.

!"#$%&'()*(+,-%&'.(

! "#$!

Band pass filter

This is a great filter. It attenuates frequencies below and above the cut-off and

leaves the frequencies at the cut-off. It is, in effect, a low-pass and a hi-pass

together. The great thing about this filter is that you can eliminate the lower and

higher frequencies and be left with a band of frequencies that you can then use

as either an effect, as in having that real mid-range type of old radio sound, or

use it for isolating a narrow band of frequencies in recordings that have too

much low and high-end.

Try this filter on synthesizer sounds and you will come up with some wacky

sounds. It really is a useful filter and if you can run more than one at a time,

and select different cut-offs for each one, then you will get even more

interesting results. Interestingly enough, band-pass filtering is used on formant

filters that you find on so many soft synths, plug-ins, synthesizers and samplers.

Notch Filter – also know as Band Reject Filter

The inverse of a band-pass is the notch filter.

This is a very potent EQ/filter. It can home in on a single frequency band, and

cut/boost it. Used specifically for ‘problem’ frequencies, the notch can be one of

the most useful filters. This is the exact opposite of the band-pass filter. It

allows frequencies below and above the cut-off and attenuates the frequencies

around the cut-off point.

In terms of the diagram shown for band-pass filtering, the area in between the

two arrows is rejected (cut out) as opposed to allowed to pass through and the

remaining frequencies below and above the cut-off are allowed to pass through.

This is the exact opposite of band-pass filtering.

In the early days of analogue synthesizers we were lucky we had a single low-

pass filter and there was a good reason for this. The low-pass filter allowed the

fundamental frequency to pass through unless the filter was closed completely

!"#$%&'()*(+,-%&'.(

! "#$!

(cut-off taken down to 0). For this reason alone it was the most commonly used

filter.

For the purposes of this book we do not need to look beyond the filter types and

how they behave. However, as this book is about effects, we will explore how a

filter can be used as an effect as opposed to simply filtering frequencies and the

best way to do this is to use modulators to affect the varying filter parameters.

The most basic form of affecting a filter is to use an envelope to shape the

filter’s response. An envelope denotes a shape and the most common envelope

parameters are ADSR (attack, decay, sustain and release); please reference the

chapter for modulators for more information on ADSR. Using an envelope and

targeting the filter we can shape the behaviour of the filter over time. The

following example uses a simple ADSR to shape filter1.

Starting with a simple waveform from Strobe it is easy to demonstrate how the

filter opens using an ADSR (envelope) and in this case it is the mod env

(modulation envelope) much as we did in the chapter on modulation.

strobe tone dry.wav

A combination of saw and sine waveforms are run through the filter with no

modulation of any sort. The next step is to assign the mod env to modulate the

filter cut-off.

!"#$%&'()*(+,-%&'.(

! "#"!

strobe tone mod env cut off.wav

The mod env is shaped to start with a slow attack and the filter cut-off responds

to the shape of the envelope. Although a similar example has been covered in

the modulation chapter I thought it prudent to create a similar example because

the next step is to modulate the resonance and the two examples together

should help in understanding the workflow.

strobe tone res.wav

The mod env is not modulating the filter resonance and this can be heard quite

distinctly.

strobe tone res lfo.wav

The LFO is set to a sine shape and it is used to modulate the filter resonance.

Quite a distinct sound.

That covers the basic envelope modulators for filter cut-off and resonance. Let

us now take this into a sound design concept and have more dynamic movement

and variety.

pad clean.wav

A nice pad without any filter shaping that goes through its natural progression

!"#$%&'()*(+,-%&'.(

! "#$!

using basic effects. Now, let us reshape the filter behaviour using the filter1

ADSR of a wonderful vsti called Albino made by Rob Papen.

pad filter adsr.wav

The filter stays closed and then opens up to allow the filter characteristics to

pass through. This gives the sound a nice swelling texture. The area we are

concerned with is the filter envelope on the left of the GUI. Here is the envelope

parameter in isolation.

A long attack value with a full decay and sustain and a midway release gives this

wonderful swelling effect. Because the attack starts later this means that the

filter opens up later. Using envelopes to shape filters is one of the most useful

ways of creating movement. We can also create the same effect opening and

then closing just by using the filter ADSR.

!"#$%&'()*(+,-%&'.(

! "##!

pad filter adsr open close.wav

By removing the sustain and shortening the decay time we have the filter

opening for a short period, then closing as the decay leads into a non-existent

sustain.

Let’s do one more example using the filter ADSR to shape the filter on pink

noise.

pink noise.wav

pink noise filt opening.wav

I have included the whole GUI here so you can evaluate the filter selection and

the ADSR. The filter is a low-pass 24dB with the cut-off set at 0 with no tracking

or resonance and the filter is wholly controlled by the filter1 ADSR; the env

(envelope) function controls the mix of the audio going through directly and

using the filter ADSR envelope, a bit like a wet/dry mix control. I have it set to

!"#$%&'()*(+,-%&'.(

! "#$!

completely use the filter1 ADSR envelope. We can take this a step further and

have the ADSR sweep the filter resonance as well as opening the filter.

pink noise filt res.wav

The resonance is now being affected by the filter1 ADSR and using the same

settings as the previous example the time taken for the filter to open and the

resonance to be swept is governed by the attack parameter of the filter1 ADSR.

However, why end there? Let’s assign a LFO to modulate the filter panning and

assign another modulator to control the rate/speed of the LFO. Basically, this

means that the frequency of the LFO will determine the speed of the filter

panning and by having another modulator, in this case filter2 env, control the

LFO rate we can create a really interesting effect whereby the filter pan will

progressively speed up and pan faster and faster.

The image above shows the settings for LFO1 using a triangle shaped LFO with a

peak frequency setting that will be achieved when the filter2 ADSR sweeps

through the frequencies by modulating the LFO rate.

!"#$%&'()*(+,-%&'.(

! "#$!

The filter 2 envelope (F2) shows a long attack value and the modulation matrix

on the right shows how the source and destinations have been assigned with

LFO1 controlling the filter1 panning but with the filter2 envelope controlling the

rate/speed of LFO1. The filter2 envelope gradually speeds up the LFO speed

which in turn speeds up the filter panning.

pink noise filt pan speed.wav

With the next example I am going to load up one of the presets from my Dark to

Light sound bank I created for Albino. The filter pans are controlled by two

different LFOs and the filter resonance is controlled by velocity. Additionally, the

filter is set to a band pass and a mix of both the direct signal and filter1

envelope shape the filter response.

albino fil res and pans.wav

Although not complicated, the use of source modulators controlling

predominantly the filter cut-off and resonance we are able to create a really

dynamic and ambient texture. It is the selection of the band pass filter that gives

this particular sound its very resonant edge.

By layering two sounds and using different modulators to control varying filter

and pitch destinations we can create large evolving sounds. I will use only the

filter and mod screen captures for the next example otherwise I will end up with

page after page of routings.

!"#$%&'()*(+,-%&'.(

! "#$!

Evolving pad layer1

Evolving pad layer2

evolving pad albino.wav

LFOs have been used for filter panning, filter resonance, oscillator pitches and

symmetries. By varying the LFO shapes and frequencies, and creating filter

envelopes, we can control varying destination parameters to create a complex

evolving sound over time.

It is now time to get a little more adventurous and use a dedicated filter device

and use different types of modulators to control varying parameters on the filter.

Using drum beat2 dry.wav and the Blue Filter we can assign a LFO to

modulate the filter frequency and create some dramatic and interesting effects.

drum beat2 bl lfo filter.wav

If you look at the image above you will see that 4 poles have been selected with

an extremely high slope, and a triangle shaped LFO has been used as the source

modulator with freq (frequency) as the destination, and because the mix is set

to fully wet (filter) we get that lovely squelchy and bouncy effect. This is a nice

and simple vst that can be used to modulate a filter but I like to go even more

!"#$%&'()*(+,-%&'.(

! "#$!

extreme and for the purposes of serious mangling I cannot think of a better vst

than Camel Audio’s Camel Phat3.

Let’s go a little extreme here and use a source modulator, in this case a square

shaped LFO, to modulate the cut-off frequency of a low-pass filter.

drum beat2 camel mad filter.wav

The lower middle section of the GUI shows that the LFO is switched on and the

‘shape’ is a square and the ‘target’ is the MMFilterCutoff (multi-mode filter cut-

off). On the right of that is the multi-mode filter and I have selected a low-pass

filter with an extremely low cut-off value with very high resonance and you can

see the basic envelope follower (env) that is reliant on the attack and release

values when fine tuning the incoming audio signal.

The env knob is an amount/intensity knob (the more you turn it clockwise the

higher the env amount/intensity). The mix has been set to fully ‘wet’. The sound

has completely changed and the loop information has been ‘smeared’ by the LFO

rate and depth amounts. Truly mad, truly lovely.

In the following example I am going to stay with the same drum loop but thin it

our using a high-pass filter but with the right modulation settings I can take this

a step further and make it musical and the real secret here is in the treating of

the kick drum and that has everything to do with timing.

!"#$%&'()*(+,-%&'.(

! "#$!

drum beat2 camel hp.wav

This time a triangle shape LFO is used to modulate the high-pass filter’s cut-off.

Leaving the attack and release values short with a small amount of env we can

get the drum loop to sound bouncy and squashed. The LFO depth and rate are

relatively high but not high enough to cause complete timing mayhem.

How about routing the LFO to modulate the env amount whilst using a band pass

filter? This will make for an interesting sound.

!"#$%&'()*(+,-%&'.(

! "#$!

drum beat2 env amt bp.wav

The ramp down shape for the LFO gives us a nice instance of a modulator ‘going

downhill’ for use of a better phrase. This allows us to have varying textures over

time which then repeats itself when retriggered. The band pass filter can be

made to sound very resonant if the bandwidth is made smaller and with the

envelope follower being pushed and controlled by the ramp down LFO we are

guaranteed to have some very interesting results.

We can use filters on evolving sounds or static sound. In the next example I will

reshape a kick drum using both band pass and notch filters.

big kick1.wav

!"#$%&'()*(+,-%&'.(

! "#$!

big kick1 camel grease.wav

The LFO shape is a ramp up (think of going uphill), which is the opposite of a

ramp down and this is routed to control the band pass filter’s low filter cut-off.

The multi-mode filter is also activated with a very low cut-off and high

resonance. The two together result in this lovely and greasy drum sound.

No example would be complete without processing a snare.

acu snare dry.wav

!"#$%&'()*(+,-%&'.(

! "#"!

acu snare camel filter.wav

Using a ramp down shaped LFO routed to the multi-mode filter cut-off with

moderate settings for env, resonance and cut-off we can create this nice funky

slap down type of effect.

Using filter modulation on any sound can work wonders and can offer a huge

range of different textures. Using the acoustic bass dry.wav sample we can

completely change the tonal quality and afford us a new texture to use in our

productions.

!"#$%&'()*(+,-%&'.(

! "#$!

acoustic bass camel dark.wav

Using both filters, band pass and low-pass, we can shape and modulate the low-

pass filter cut-off while running the signal through the band pass. Triangle

shaped LFO works really well with this sound and has changed the bass into

another very usable and distinct texture; a great way to synthesize an acoustic

sound into a more synthetic one.

Using the same bass sound we can manipulate it even further.

!"#$%&'()*(+,-%&'.(

! "#$!

acoustic bass camel phat.wav

Using a very low rate for the sine shaped LFO we can make the bass wobble and

by driving the resonance on the band pass filter and coupling it with the

modulation over the high-pass filter cut-off we get the aggressive and fat bass

texture.

Let’s try another example by reshaping the electric keys.wav line into a

completely different colour.

!"#$%&'()*(+,-%&'.(

! "##!

electric keys camel trem.wav

The settings speak for themselves but what is important is the use of a sine

shaped LFO because it is this smooth cyclic shape that makes the ‘tremolo’ effect

sound so fluid.

I will end this chapter with a few more preset examples taken from my Albino

sound bank as they provide a good insight into what can be achieved with

modulators controlling filter cut-offs, pans and resonances.

albino filter efx.wav

Only one filter is being used here, band pass, but the real heart of this preset is

!"#$%&'()*(+,-%&'.(

! "#$!

the use of LFOs to modulate oscillator pitch, filter cut-off and resonance, and a

single LFO used to control the rate/speed of another LFO. The result is a

dynamic sound effect.

I mentioned earlier that anything, within reason, could be used as a source

modulator and one of the most potent is an arpeggiator. An arpeggiator is the

equivalent of a sequence of notes, chords or modulator being played back at a

defined speed and division. Think of it as a short repeated sequence.

The following are a selection of arpeggiator pre3sets that have the arpeggiator

modulating filter cut-offs, resonances, pitch and so on. I won’t list each and

every one but provide a screen shot of the mod matrix so you can ascertain

what is routed where. Never ignore the power of an arpeggiator as anything that

can be used as a source modulator that varies over time has to be a really useful

tool.

Here is a nice little scratch effect using only noise and a simple mod matrix

where two filters are used and two arpeggiators are routed to control the cut-

offs of each at varying time divisions. Additionally, two LFOs are used to

modulate the filter pans.

albino filter scratch.wav

Here is another that uses an arpeggiator to control filter cut-off. The use of

additional LFOs to control pans makes this an interesting repeated sequence.

!"#$%&'()*(+,-%&'.(

! "#$!

albino filter hook.wav

We can also create interesting sweet sequences by assigning the arpeggiator to

modulate the cut-off at varying values.

albino swt seq.wav

The next example is actually a cute variation of a chord using one LFO to control

the filter pan and the arpeggiator to control the filter cut-off and symmetry.

!"#$%&'()*(+,-%&'.(

! "#$!

albino weeping pans.wav

Let’s end with a throbbing synth line that uses the arpeggiator to control filter

cut-off and symmetry.

albino throb synth.wav

Filters and their modulation have been firm favourites with sound designers for a

long time and with the advent of dedicated filter devices the realms of

production have now embraced this wonderful process.

!"#$%&'()*(+,-%&'.(

! "#$!

Vocoder

Vocoders have been around for a long time and there has now been a

resurgence of this effect/process. I was in two minds as to which chapter to put

the vocoder section in but came to the conclusion that as we are dealing with

filters we might as well go the whole way and include vocoders as an effect

within this chapter.

A vocoder allows the sound character of the source (modulator) to affect a

destination sound (carrier). In other words, the characteristics of one sound are

used to modulate the characteristics of another sound. The modulator is fed

through a bank of filters that analyse the response and frequency characteristics

and this in turn controls the level of carrier signal which is also fed through a

bank of filters (the level of signal going into each filter is controlled by the

modulator). The more filter bands the more control and definition over the

signal.

The classic case of using a vocoder is to use a voice (fed through a microphone)

to modulate the carrier which can be anything that has a nice sustained

character and pad sounds came top of the list. However, today we use vocoders

with varying modulators and carriers and create some of the most innovative

and interesting sounds.

For the next few examples I will use vocal samples and modulate them with

Midi. I would like to take this opportunity to thank Tanikye and GAM for use of a

variety of vocal lines sung by Tanikye.

tanikye vocals bv1.wav

A not too complex vocal line sung dry.

!"#$%&'()*(+,-%&'.(

! "#$!

Using Cubase SX3 as the DAW and routing the vocoder on the Midi output

channel and using it as an insert on the audio channel where the vocal sits we

can modulate the vocal line by using Midi; in this instance I am playing two

minor chords and have used the standard vocoder in Cubase set to play 7ths.

vocoder tanikye1.wav

Using the various filters and assigning specific parameters to further modulate

the carrier we can create really evolving sounds and textures. By using the

minor chords to modulate the carrier we can literally change the harmonic

content of the carrier.

We can also modulate the carrier using an audio file. We are not limited to just

trigger by Midi. I will use a drum beat to modulate a pad sound to create a

completely new texture, and one that I quite like as it has kept the ‘vocal’ aspect

of the filters.

We will use the following two audio files:

vocoder drum beat 140 bpm.wav

vocoder pad 140 bpm.wav

!"#$%&'()*(+,-%&'.(

! "#$!

vocoder audio to audio.wav

The drum beat is the modulator and the pad sound is the carrier. You can still

hear some of the drum elements and the varying triggered levels that go into

the filter bank are quite evident.

Using the same setup and playing around with the vocoder parameters we are

able to create a more musical line without the drums being evident.

!"#$%&'()*(+,-%&'.(

! "#"!

vocoder audio to audio 2.wav

Extending the bandwidth and setting minimum and maximum frequency ranges

and using the noise parameter we can create this lovely harmonic texture. If

look at the bottom right of the GUI you will see that I have selected 10 filter

bands to play with. I will use one more example of this setup but alter the noise

parameter and drop down to 8 filter bands and you will notice the difference in

texture and definition.

vocoder audio to audio 3.wav

A slightly less detailed but meatier texture that sounds as if it could sit behind a

beat and add some colour to a mix.

In the following example we will use the vocal line to modulate the pad line

(carrier) and apply a lot of filtering with the existing reverb to create a

‘whispering’ effect.

!"#$%&'()*(+,-%&'.(

! "#$!

vocoder audio to audio 4.wav

A really filtered and breathy effect by having the vocal line modulate the carrier

which is a pad sound. The use of 24 bands of filters makes all the difference here

as more detail and ‘warmth’ can be applied as there are more filters to use. The

bandwidth and frequency ranges give us additional control over the behaviour of

the modulator and carrier.

It is also possible to have both the modulator and carrier signals playing

together by using the talk thru function. Using the following as the carrier and

modulating it with Midi:

vocoder bass dry.wav

A 94 BPM bass line with no effects applied.

vocoder talk thru.wav

Dirty yet dynamic and this is achieved with selecting the desired min and max

frequencies whilst mixing it with the talk thru function.

The final example uses the more traditional vocoder sound but is mixed with the

original to allow for a slightly thicker and more interesting texture.

!"#$%&'()*(+,-%&'.(

! "#$!

vocoder talk thru trad.wav

This is a little more like the talk box type of effect and features a narrower

frequency range but with a full bandwidth. The talk thru allows the mixing of the

modulator signal with the carrier and a little high thru brings in the more raspy

flavour.

This chapter has dealt with the subject of filters and their manipulations using

varying source modulators but nothing is more educational and fun than you

exploring this wonderful process and trying different source modulators to

varying destinations.