Author Archives: Nigel Redmon

Evaluating filter frequency response

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 | 18 Comments

Cascading filters

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 | 15 Comments

Filters for synths—the 4-pole

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

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

Audio Signal Processing for Music Applications

I’d like to recommend this excellent—and free—online course: Audio Signal Processing for Music Applications by Prof Xavier Serra, Prof Julius O Smith, III The brief: In this course you will learn about audio signal processing methodologies that are specific for music … Continue reading

Posted in Uncategorized | 1 Comment

Dither—The Naked Truth video

This video presents the “naked truth” on dither and truncation error, by stripping away the original signal of a musical clip and listening at different bit levels. I boost the error to a normalized audio volume for easy comparison of … Continue reading

Posted in Digital Audio, Dither, Video | 2 Comments

Dither widget

Posted in Digital Audio, Dither, Widgets | Leave a comment

Audio Dither Explained video

This video discusses the how and why of dither.

Posted in Digital Audio, Dither, Video | 1 Comment

More about source code

I was admonished (in not a nice way—not terribly rude, but quite to the point that I don’t know what I’m doing) by an anonymous visitor, who concluded that I don’t know much about C++ and maybe should have written … Continue reading

Posted in Source Code | 7 Comments

Pole-Zero placement v2

Pair Pole mag Pole angle Pair Zero mag Zero angle Sample rate (Hz) linearlog Plot A new pole-zero calculator An JavaScript remake of the old Java-based pole-zero placement applet—visit that page for tips on pole-zero locations for standard biquads. The … Continue reading

Posted in Biquads, Digital Audio, Filters, IIR Filters, Widgets | 13 Comments