Category Archives: FIR Filters

Filter frequency response grapher

Posted on December 8, 2016 by Nigel Redmon

Here’s a tool that plots frequency response from filter coefficients. Hz linearlog 10log 2 Plot auto40 dB30 dB20 dB10 dB0 dB-10 dB-20 dB-30 dB-40 dB Max 60 dB80 dB100 dB120 dB140 dB160 dB180 dB Range a coefficients (zeros) b coefficients … Continue reading →

Posted in Biquads, Filters, FIR Filters, IIR Filters, Widgets | 15 Comments

Evaluating filter frequency response

Posted on December 1, 2016 by Nigel Redmon

A question that pops up for many DSP-ers working with IIR and FIR filters, I think, is how to look at a filter’s frequency and phase response. For many, maybe they’ve calculated filter coefficients with something like the biquad calculator … Continue reading →

Posted in Biquads, FFT, Filters, FIR Filters, IIR Filters | 27 Comments

Convolution—in words

Posted on March 5, 2012 by Nigel Redmon

Convolution is a convoluted topic—and that’s what it means (convoluted, from Merriam-Webster : “Extremely complex and difficult to follow. Intricately folded, twisted, or coiled.”). Really, it’s more difficult to explain why you would want to use convolution than it is … Continue reading →

Posted in Convolution, Digital Audio, FIR Filters, Impulse Response, Reverb | Leave a comment

A closer look at upsampling filters

Posted on December 11, 2010 by Nigel Redmon

Interpolation type:NoneZero-order holdLinearSinc 1Sinc 2Sinc 3  Show impulse response Sweep! In this demonstration, we generate a sine wave sweep from low in the audio band to near the Nyquist Frequency, which is half the sample rate. You can view it … Continue reading →

Posted in Aliasing, Digital Audio, Filters, FIR Filters, Impulse Response, Sample Rate Conversion, Widgets | 1 Comment

Sample rate conversion: up

Posted on December 5, 2010 by Nigel Redmon

Once we have a suitable set of FIR filter coefficients from our windowed sinc calculator, it’s time to apply them. Again, our recipe for doubling the sample rate: 1) Insert a zero between existing samples. (This is the upsampling step, … Continue reading →

Posted in Aliasing, Convolution, Digital Audio, Filters, FIR Filters, Sample Rate Conversion | 7 Comments

Building a windowed sinc filter

Posted on December 5, 2010 by Nigel Redmon

As promised, here’s our windowed sinc calculator for building a 2x oversampling filter:  Factor  Length  Rejection  Gain Notes: Use the Tab or Enter keys to effect changes (most browsers), or press Calculate. The frequency axis is in multiples of the … Continue reading →

Posted in Digital Audio, Filters, FIR Filters, Impulse Response, Sample Rate Conversion, Widgets | 14 Comments

Towards practical resampling

Posted on November 23, 2010 by Nigel Redmon

In a previous article, we looked at sample rate conversion in the frequency domain. Let’s take a quick second look in the time domain as reinforcement of principles behind sample rate conversion, before developing a practical rate convertor. In an … Continue reading →

Posted in Digital Audio, Filters, FIR Filters, Impulse Response, Sample Rate Conversion | 7 Comments