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Books on Digital Filters

I need to implement a cut-off filter of an old analogue synthesizer as a digital filter. Since standard simple IIR filters aren't good enough, I'm looking for a good book on the subject so I could design the filter myself. The book should have a thorough discussion of IIR filter design (second-order and higher) and it should be readable to some extent. :-)

I already own a copy of DSP First by McClellan etc, which is very readable but too simple. Most books also just give a few examples of second-order filters without explaining their design, which doesn't help me much.

Any recommendations? Thanks in advance.

Frederik Slijkerman
Friday, March 07, 2003

Analogue synths used low pass resonant filters for that wah wah effect.

Matthew Lock
Friday, March 07, 2003

I know, but simple second-order resonant digital filters that you find on the web sound too harsh and "digital". This is because the peak in the frequency spectrum that they create is too narrow.

Frederik Slijkerman
Friday, March 07, 2003

Pretty good book. And free:

http://www.dspguide.com/pdfbook.htm

Sergio Massara
Friday, March 07, 2003

Well the first thing is to establish what the analogue filter is that you are trying to emulate. What is the original design (get circuit diagrams if you can) Does it get driven into non-linearities? (that's analogue "warmth") How does cutoff frequency track through the range (otherwise sweeps will sound different), and so on.

Sometimes the architecture of the analogue filter will make the choice of digital filter pretty obvious (say in the case of State Variable Filters), but the devil is in the details, and the only way to get those is a lot of simulations, measurements and listening.

Jon Hodgson
Sunday, March 09, 2003

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