Filters
A filter is a manipulation tool which can alter the relative balance of rates within a sound.
What is a filter?
A filter changes the frequency of making a sound by making parts of it. Filters allow you to focus on these parts of the world, or to take away parts that you do not like, such noise or ‘hiss’. As we learn in Pitch and Soundscape Music , sounds are often made up of many different frequency parts.
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
Listen and then compare this with the filtered sound.
1. Filtered Sound
How does it compare with the unfiltered sound?
2. Original Sound
Listen and then compare this with the filtered sound.
2. Filtered Sound
How does it compare with the unfiltered sound?
3. Original Sound
Listen and then compare this with the filtered sound.
3. Filtered Sound
How does it compare with the unfiltered sound?
4. Original Sound
Listen and then compare this with the filtered sound.
4. Filtered Sound
How does it compare with the unfiltered sound?
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, as shown 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 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 the low frequency portions of a sound.
You can hear only low frequencies, all of the key jangles have been removed.
Composition Tip
Low-Pass Filters can be useful when we want to highlight 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 the high frequency portions of a sound.
All the parts of the sound have been removed, leaving only the jangling of the keys. We no longer hear the closing thump of the door.
Composition Tip
High-Pass Filters can be very useful for removing 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.
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.
Composition Tip
Being able to focus on a 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 at a specific frequency. The quality of the filter will affect its width.
In this example, only a narrow band of sound is removed. We can see this clearly in the spectrogram and we hear that this part of the sound is missing.
Composition Tip
The Band-Reject Filter may be useful for removing hum or noises that fall into the mid frequency range of a recording.
Fact
The bass and treble controls on your stereo radio are filters.
When to Use Filters?
Filters allow us to transform the frequency of makeup of sounds. They can be very useful. We can use filters to balance noise, removing very large portions of the frequency or Combined with automation , filters can be very useful in creating gesture and a sense of movement. We can use a filter sweep to draw people ‘s attention to different parts of sound and to carry the listener on a journey into sounds.
Activity
Load up a session in Compose with Sounds . Try to make use of filters in a composition.
