EARS 2

Discover the exciting world of electroacoustic music and learn to make music with sounds.

Filters

FilterCombi

A filter is a manipulation tool which can alter the relative balance of frequencies within a sound.

What is a filter?

A filter changes the frequency makeup of a sound by making parts of it weaker.

Filters allow you to focus on parts of a sound that are of interest to you, or to take away parts that you don’t like, such as noise or ‘hiss’.

As we learnt in Pitch and Soundscape Music, sounds are often made up of many different frequency parts.

Different Frequency Parts – Clock Spectrogram

Spectrogramme d'une horloge

By viewing the SpectrogramA way of visualising sounds that provides information about the frequencies that make up the sound.More infospectrogram of a sound, it is easy to see the different frequency parts which make up that sound.

Using filters, we can change the balance of these frequency parts, removing some to make others stand out.

Filters in Action

Below are some sounds which have been filtered.

  • Can you hear the difference between the sounds before and after filtering?
  • What has changed?

1. Original Sound

Unfiltered

Listen and then compare this with the filtered sound.

Aeroplane


1. Filtered Sound

Filtered

How does it compare with the unfiltered sound?

Aeroplane_bp



2. Original Sound

Unfiltered

Listen and then compare this with the filtered sound.

CarPass


2. Filtered Sound

Filtered

How does it compare with the unfiltered sound?


CarPass_hp



3. Original Sound

Unfiltered

Listen and then compare this with the filtered sound.

GravelCrunch


3. Filtered Sound

Filtered

How does it compare with the unfiltered sound?

GravelCrunch_LP



4. Original Sound

Unfiltered

Listen and then compare this with the filtered sound.

DryLeaves


4. Filtered Sound

Filtered

How does it compare with the unfiltered sound?

DryLeaves_bp



Filter Properties

Filters have two main controls:

  • Frequency: The frequency at which the filter operates.
  • Quality: The width and shape of the filter (narrow or wide/gentle or steep).

By altering these controls, we can change the output sound, as demonstrated in the video:


Filter Types

There are several types of filter, and each creates a different type of effect.

Each type is explained below, with the same original sound being transformed by the different filters.

Original Sound - Keys and Door

This sound contains many different parts - the high jangle of the keys and the low thud of the door closing. Listen and compare it with the following filtered versions of the same sound.

 

Low-Pass Filter:

Allows all frequencies lower than its cut-off point to pass (for example, if the cut-off frequency is set at 500 Hertz (Hz), all of the frequencies over 500 Hz will disappear). Does not allow any higher frequencies to pass. This filter is best used to remove unwanted high sounds, or to highlight only the low frequency portions of a sound.

KeysAndDoor_lp

Low-Pass Filter

You can hear only low frequencies, all of the key jangles have been removed.

LP

Composition Tip

Low-Pass Filters can be useful when we want to highlight only the bass frequencies of a sound.

 

High-Pass Filter:

Allows all frequencies higher than its cut-off point to pass. Does not allow any lower frequencies to pass. This filter is best used to remove unwanted bass sounds, or to highlight only the high frequency portions of a sound.

KeysAndDoor_hp

High-Pass Filter

All low parts of the sound have been removed, leaving only the jangling of the keys. We no longer hear the low thump of the door closing.

HP

Composition Tip

High-Pass Filters can be very useful for removing low background noise, like the rumble of traffic from recordings.

 

Band-Pass Filter:

Allows one band of sound to pass through. Best used to highlight frequencies of sound in a specific area. The quality of the filter will affect its width.

KeysAndDoor_bp

Band-Pass Filter

Only a narrow band of sound is allowed through the filter. This means that we lose both the high and low frequency parts of the sound.

BP

Composition Tip

Being able to focus on one specific area of the sound allows us to highlight a specific aspect that might be unique.

 

Band-Reject Filter:

Will not allow a certain band of sound to pass through. This filter is best used to remove sounds at a specific frequency. The quality of the filter will affect its width.

KeysAndDoor_br

Band-Reject Filter

In this example, only a narrow band of sound is removed. We can see this clearly in the spectrogram and we hear that this middle part of the sound is missing.

BR

Composition Tip

The Band-Reject Filter can be useful for removing hum or noises that fall within the mid frequency range of a recording.

 

Fact

The bass and treble controls on your stereo or car radio are filters.


When to Use Filters?

Filters allow us to transform the frequency makeup of sounds. They can therefore be very useful to us.

We can use filters to balance sounds, removing very loud portions of the frequency range or boosting areas of interest which are quiet.

Combined with AutomationA tool that allows you to change the variable parameters of a sound over time.More infoautomation, filters can be very useful in creating GestureA Gesture is an energy trajectory (pathway), moving from one point to another.More infogesture and a sense of movement.

We can use a Filter SweepThe combination of Automation and a Filter, creating a dynamic sound gesture.More infofilter sweep to draw people’s attention to different portions of sound and to carry the listener on a journey into sounds.

Activity

Load up a session in Compose with Sounds and begin to explore filters yourself.

Try to make use of filters in a composition.