Search Results for: filter

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

Cascading filters

Posted on September 29, 2016 by Nigel Redmon

Sometimes we’d like to cascade biquads to get a higher filter order. This calculator gives the Q values for each filter to achieve Butterworth response for lowpass and highpass filters. Order: 234567891011121314151617181920 Q values: You can calculate coefficients for all biquad … Continue reading →

Posted in Biquads, Filters, IIR Filters, Widgets | 38 Comments

Filters for synths—the 4-pole

Posted on February 22, 2016 by Nigel Redmon

The last post noted that the two most popular synthesizer filters are the 2-pole state variable, and the 4-pole “Moog style”. And we started with the state variable—simple, popular, and delivering multiple filter outputs (lowpass, bandpass…) simultaneously. Here, we’ll follow … Continue reading →

Posted in Digital Audio, Filters, IIR Filters, Synthesizers | 5 Comments

Filters for synths–starting out

Posted on February 21, 2016 by Nigel Redmon

We haven’t developed a synth filter here yet… Filters we’ve presented Biquads. While they are useful for many simple cases of filtering, they are not a good choice for analog synthesizer emulation. Most notably, they are poorly suited to time-varying … Continue reading →

Posted in Digital Audio, Filters, IIR Filters, Synthesizers | Leave a comment

A one-pole filter

Posted on December 15, 2012 by Nigel Redmon

Here’s a very simple workhorse of DSP applications—the one-pole filter. By comparison, biquads implement two zeros and two poles. You can see that our one-pole simply discards the zeros (the feed-forward delay paths) and the second pole (feedback path): We … Continue reading →

Posted in DC Blocker, Digital Audio, IIR Filters, Source Code | 40 Comments

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

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

The digital state variable filter

Posted on March 2, 2003 by Nigel Redmon

The digital state variable filter was described in Hal Chamberlin’s Musical Applications of Microprocessors. Derived by straight-forward replacement of components from the analog state variable fiter with digital counterparts, the digital state variable is a popular synthesizer filter, as was its … Continue reading →

Posted in Digital Audio, Filters, IIR Filters | 22 Comments

Analog digital continuous discrete

Posted on January 16, 2023 by Nigel Redmon

Digital and analog. We often think of them, mistakenly, as equivalent things in different domains. But that’s a misunderstanding, and we often use the terms incorrectly. For instance, run a mic through a preamp and get a signal, we know … Continue reading →

Posted in Digital Audio, Fun Facts | Leave a comment