Filters

Digital Signal Processinghakon.kvidal@nmh.no

To filter

• To filter is to select certain elements with desired properties from a larger set.

• A filter will modify the amplitude of the partials according to their frequency

Lowpass (HP)

• Attenuates frequencies above cut-off frequency fc

• Sometimes lowpass filters are called highcut.

Highpass (HP)

• Attenuates frequencies below cut-off frequency fc

• Sometimes highpass filters are called lowcut.

Bandpass (BP)

• Select frequencies between a lower cut-off frequency fcl and a higher cut-off frequency fch

• Frequencies below fcl and higher than fch are attenuated

Bandreject (BR)

• attenuate frequencies between a lower cut-off frequency fcl and a higher cut-off frequency fch

• Frequencies below fcl and higher than fch are passed

Resonance

• Amplifies the frequencies around the cutoff frequency

Stepness

• First-order: 6 dB roll-off pr. octave• Second-order: 12 roll-off pr. octave

Equalizer

• a series of shelving and peak filters, which are controlled independently

Practice your listening skills

• Harmans How to Listen• Free application for Windows and OS X. • Download from

http://harmanhowtolisten.blogspot.no/

References

• Filter design, http://en.wikipedia.org/wiki/Filter_design

• Low-pass filter, http://en.wikipedia.org/wiki/Low-pass_filter

• Zölzer, Udo (2011): DAFX Digital Audio Effects. Second Edition.