DSP - Filtering frequencies using DFT

Posted by Trap on Stack Overflow See other posts from Stack Overflow or by Trap
Published on 2010-05-20T16:58:45Z Indexed on 2010/05/21 11:50 UTC
Read the original article Hit count: 337

Filed under:

dsp

|

dft

|

fft

I'm trying to implement a DFT-based 8-band equalizer for the sole purpose of learning. To prove that my DFT implementation works I fed an audio signal, analyzed it and then resynthesized it again with no modifications made to the frequency spectrum. So far so good.

I'm using the so-called 'standard way of calculating the DFT' which is by correlation. This method calculates the real and imaginary parts both N/2 + 1 samples in length. To attenuate a frequency I'm just doing:

float atnFactor = 0.6;
Re[k] *= atnFactor;
Im[k] *= atnFactor;

where 'k' is an index in the range 0 to N/2, but what I get after resynthesis is a slighty distorted signal, especially at low frequencies.

The input signal sample rate is 44.1 khz and since I just want a 8-band equalizer I'm feeding the DFT 16 samples at a time so I have 8 frequency bins to play with.

Can someone show me what I'm doing wrong? I tried to find info on this subject on the internet but couldn't find any.

Thanks in advance.

© Stack Overflow or respective owner

Related posts about dsp

any good free C DSP library?

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi everybody I am developing an application to process geophysical signals; Right now I have done everything in octave and its digital signal processing toolbox, speed is not bad, however the application specifications say I need to port to the final algorithm to C; I am doing lots of filtering,… >>> More
DSP - How are frequency amplitudes modified using DFT?

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to implement a DFT-based equalizer (not FFT) for the sole purpose of learning. To check if it works I took an audio signal, analyzed it and then resynthesized it again with no modifications made to the frequency spectrum. So far so good. Now I tried to silence some frequency bands, just… >>> More
Embedded Systems using FlowStone DSP Programming Language for Windows

as seen on Code Project - Search for 'Code Project'
Developing Embedded Systems Using FlowStone DSP >>> More
TMS320C64x Quick start reference for porgrammers

as seen on Stack Overflow - Search for 'Stack Overflow'
Hello Is thare any quickstart guide for programmers for writing DSP-accelerated appliations for TMS320C64x? I have a program with custom algorythm (not the fft, or usial filtering) and I want to accelerate it using multi-DSP coprocessor. So, how should I modify source to move computation from main… >>> More
Is Objective C fast enough for DSP/audio programming

as seen on Stack Overflow - Search for 'Stack Overflow'
I've been making some progress with audio programming for iPhone. Now I'm doing some performance tuning, trying to see if I can squeeze more out of this little machine. Running Shark, I see that a significant part of my cpu power (16%) is getting eaten up by objc_msgSend. I understand I can speed… >>> More

Related posts about dft

Hitachi DFT hangs - Causes and workarounds?

as seen on Super User - Search for 'Super User'
Hitachi DFT hangs (it gets all the way to "Loading DFT" and hangs with a blinking cursor) when I use it on various computers (the latest computer to hang being a Dell Vostro 1000 laptop) and works on others. What determines when it will hang and when it won't? What similar program can I use (boot… >>> More
DSP - Filtering frequencies using DFT

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to implement a DFT-based 8-band equalizer for the sole purpose of learning. To prove that my DFT implementation works I fed an audio signal, analyzed it and then resynthesized it again with no modifications made to the frequency spectrum. So far so good. I'm using the so-called 'standard… >>> More
DSP - How are frequency amplitudes modified using DFT?

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to implement a DFT-based equalizer (not FFT) for the sole purpose of learning. To check if it works I took an audio signal, analyzed it and then resynthesized it again with no modifications made to the frequency spectrum. So far so good. Now I tried to silence some frequency bands, just… >>> More
Simple in-place discrete fourier transform ( DFT )

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm writing a very simple in-place DFT. I am using the formula shown here: http://en.wikipedia.org/wiki/Discrete_Fourier_transform#Definition along with Euler's formula to avoid having to use a complex number class just for this. So far I have this: private void fft(double[] data) { … >>> More
DSP - Problems using the inverse Fast Fourier Transform

as seen on Stack Overflow - Search for 'Stack Overflow'
I've been playing around a little with the Exocortex implementation of the FFT, but I'm having some problems. First, after calculating the inverse FFT of an unchanged frequency spectrum obtained by a previous forward FFT, one would expect to get the original signal back, but this is not the case… >>> More