Álvaro Castro hat gesagt: // Álvaro Castro wrote:

Finally, I would like to know what's the best way to work with pure (or almost pure) frecuencies. That's the reason I want to build an equalizer. I would like to add, increase, delete or decrease specific frecuencies. Is that posible with Pure-data??

I am contemplating something similar for some days now: I would like to have something like Native Instruments "Spectral Delay" in PD. Using the fourier transformation is the way to go. But this is non-trivial mathematics and DSP programming stuff and I am still in the research phase. You might want to look at all the patches in 4.fft.examples and for some theory read www.dspdimension.com.

Basically you should be able to analyze audio data into the frequency domain, cut out or change some frequencies and resynthesize this sound with an inverse fft. 07.tinbell.pd shows how to boost certain frequencies with fft. I don't know if this would be appropriate for an equalizer, though, as the sound could get changed (frequency smear etc.) But in a spectral delay I could live with this.

But I still don't know how to cut out the frequencies :(

Maybe some dsp guru can show this? If you find out how this is done please post it here.

bye,

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On Tue, 28 Aug 2001 02:42:12 +0200 (CEST) Álvaro Castro alvcastro@yahoo.es wrote:

Hi all!!

Some days ago I posted an e-mail asking for help for building an equalizer. I didn't get many help, that's the reason I write again. If I'm writing to the wrong list, please tell me. I just want to know the basics of an equalizer so I can start working. As you see, I'm a beginner, but I don't know how to start.

the main reason you probably haven't received much help is because this is not really a pd question but a general dsp question. so ideally you would look into some dsp resources, where you will find that you need to know a fair amount about digital filtering to make an equalizer, then maybe you would get some help on building filters in pd.

I choosed to learn PD instead of other sound programs or programming languages because I thought it was very powerful and not very difficult to learn. But when I started working with PD I discovered that one of the most important things for me (the low and high pass filters) don't work very powerfully. I tried filtering a sample and I realized that the filters didn't cut TOTALLY the frequencies they just decreased the amplitude a little bit.

this is common with digital filters... to get a really sharp roll off you normally need a more complicated filter... you can also try recursively applying the same filter...

Finally, I would like to know what's the best way to work with pure (or almost pure) frecuencies. That's the reason I want to build an equalizer. I would like to add, increase, delete or decrease specific frecuencies. Is that posible with Pure-data??

well, adding frequencies is easy... [osc~] and [+~] :)

Thank you very much for your time! I will appreciate any answer, because I don't know what to do now!!

there is a dsp book available for download at www.dspguide.com, it's reasonably accessible as an introductory text.

pix.