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Author Topic: Filter Algorithms  (Read 7356 times)

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phate

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Filter Algorithms
« on: September 22, 2008, 05:04:34 »

Milkytracker has a nice set of filters, and I know there are people around here who know a thing or two about audio processing, so I was wondering if any of you know where I can find decent resources on writing filtering algorithms. I have a decent background in digital signal processing, and I've been using Max/MSP for a few years now, but I still don't know much about the inner workings of FIR filters and Fourier transforms.

So I was wondering, what would any of you suggest for learning more about this sort of thing? I'd like to begin work on some cross-platform synthesis/audio editing tools, but until I have a firm grasp on how this stuff works, I can't really do much.
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pailes

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Re: Filter Algorithms
« Reply #1 on: September 22, 2008, 18:11:54 »

I recommend reading the first chapters of the DSP Guide: www.dspguide.com
No need to dig through the entire book, but it's worth reading the first few chapters.
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phate

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Re: Filter Algorithms
« Reply #2 on: September 22, 2008, 21:46:01 »

Thanks a ton. This is an incredible resource.

I'll probably read most of it simply because I'm interested.
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urban soul

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Re: Filter Algorithms
« Reply #3 on: September 24, 2008, 03:38:36 »

The simple biquad formula found in max is one of the best sounding filters here. Dont waste your time with pseudo analogue crap as long as your name is propeller_heads. Good sounding resonance type LP filters are hard to get close to. Nobody will tell you how to do it. For good sounding resonance you will need an overdrive/saturation module before the filter.

dspguide is fine. Pohlmann "Principles of Digital Audio" is better ($$$).

edit: Good luck.
As mentioned Reason is state of the art. To get close to that a lot of work will be necessary: responses of knobs are not linear - sometimes it is as simple as that. They use a homegrown filter formula too, i am pretty sure. Knowledge of tube design and a pair of good ears would be helpful in this respect. Tube design is BTW a fairly deep topic. Learn how to program a good K2. (Tubes have a quadratic characteristic + complicated saturation) I can send you papers if you are interested.
« Last Edit: September 24, 2008, 03:56:04 by urban soul »
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phate

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Re: Filter Algorithms
« Reply #4 on: September 24, 2008, 05:14:03 »

I need a bunch of filters. I'm working on a sample-based synthesis toolkit, so I'll need every bit of DSP code I can get my hands on. Right now though, I'm just trying to get some functional HP/LP/BP filters set up. Maybe a nice graphical EQ.

Also, what is all of this about Reason? There are a number of DAWs and VSTs that offer great sounding filters, but I'm confused as to how this is relevant to my question. I'm not trying to do anything terribly fancy ATM, I just need some basic filters for sound sculpting.

Thanks for the recommendation though. I'm a bit strapped for cash right now, but maybe I'll look into it later.
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urban soul

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Re: Filter Algorithms
« Reply #5 on: September 24, 2008, 13:15:09 »

Bits of (c/c++) code can  be found all over the net... e.g.

http://www.dspguru.com/

What environment are you using for development?

What about Reason? Nothing. I disagree that there are a number of DAWs and VSTs that offer great sounding filters, but I am not interested in that sort of discussion.
« Last Edit: September 24, 2008, 13:27:41 by urban soul »
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phate

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Re: Filter Algorithms
« Reply #6 on: September 24, 2008, 18:34:17 »

I'm using standard C and the Nintendo DS. The idea is to get a decent audio editor/sample-based synthesis toolkit going so that the people using Nitrotracker and other sample-based DS music apps will have something nice to prepare their sample material, without having to run to a computer to do it.
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urban soul

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Re: Filter Algorithms
« Reply #7 on: September 24, 2008, 22:05:19 »

most pd externals are written in plane C (open source). http://maxobjects.com/
Audacity code may also be worth a look.
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pailes

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Re: Filter Algorithms
« Reply #8 on: September 24, 2008, 22:12:18 »

Bits of (c/c++) code can  be found all over the net... e.g.

http://www.dspguru.com/

I would suggest reading the basics of DSP first (e.g. in DSP guide) and then start with FIR filters. There is a chapter about constructing FIR high/lowpass filters. This is very interesting reading, especially when you have never constructed a filter kernel for a basic FIR filter before.
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urban soul

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Re: Filter Algorithms
« Reply #9 on: September 24, 2008, 22:35:31 »

yes, dspguide is great stuff and its free. Just want to mention that FIR and IR filters are different concepts. This is all very clear described in dspguide. I personally avoid realtime implementations which depend on FFT because of artifacts in the time domain (windowing), but this is sort of OT here. 
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