Category Archives: Digital Audio

Biquad calculator v2

Posted on October 13, 2013 by Nigel Redmon

Type:lowpasshighpassbandpassnotchpeaklow shelfhigh shelfone-pole lpone-pole hp Plot:linearlog Sample rate (Hz) Fc (Hz) Q Gain (dB) Here’s an update of the biquad calculator. It adds one-pole highpass and lowpass filters, and frequency, Q, and gain sliders. The sliders cover the range of … Continue reading →

Posted in Biquads, Digital Audio, Filters, IIR Filters, Widgets | 98 Comments

Envelope generators—ADSR Part 1

Posted on June 1, 2013 by Nigel Redmon

After discussing the exponential decay of the one-pole filter in a recent article, I couldn’t help but think about envelope generators. Besides, it would be handy to have one to test out some of these other components I’ve been writing … Continue reading →

Posted in Envelope Generators, IIR Filters, Synthesizers | Tagged | 1 Comment

Wavetable oscillator video

Posted on May 27, 2013 by Nigel Redmon

If you find this video helpful, let me know, and I’ll work more video demonstrations into articles.

Posted in Aliasing, Synthesizers, Video, Wavetable Oscillators | Tagged | 6 Comments

Perspective on dither

Posted on March 24, 2013 by Nigel Redmon

Recently, I’ve had lengthy discussions on the topic of dither with a couple of different people—of opposite views. One believes that everything should be dithered, including truncations to 24-bit. The other feels that dither is a waste of time even … Continue reading →

Posted in Dither | 4 Comments

Replicating wavetables

Posted on March 3, 2013 by Nigel Redmon

My WaveTableOsc object uses a series of wavetables that are copies of single-cycle waveforms pre-rendered at a progressively smaller bandwidth. By “replicating wavetables” I mean taking a full-bandwidth single cycle waveform, and using it to make a complete set of … Continue reading →

Posted in Oscillators, Source Code, Wavetable Oscillators | Tagged | 53 Comments

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 note about de-normalization

Posted on December 3, 2012 by Nigel Redmon

One ugly thing that we need to be aware of, especially for filters, is the de-normalization of numbers. Basically, computer processors try to keep floating point numbers normalized—they try to keep them in the binary form 1.xxxxxx (where each x … Continue reading →

Posted in Digital Audio, Math | 1 Comment

Biquad C++ source code

Posted on November 26, 2012 by Nigel Redmon

I don’t want to get into the business of teaching people how to code—there are a huge number of free resources available on the internet to that do that. But I’ll give a small taste for those trying to get … Continue reading →

Posted in Biquads, Digital Audio, Filters, IIR Filters, Source Code | 99 Comments

A wavetable oscillator—end notes

Posted on November 18, 2012 by Nigel Redmon

I wrote the wavetable oscillator code from scratch as I wrote this series of articles, using just the thought process I gave. Hence, no references to other articles on wavetable oscillators. The concept of a phase accumulator is fairly obvious; … Continue reading →

Posted in Digital Audio, Oscillators, Wavetable Oscillators | Tagged | 13 Comments

A wavetable oscillator—the code

Posted on May 25, 2012 by Nigel Redmon

The wavetable oscillator code follows the basic structure of most audio processing blocks, with three types of functions: at the start: initialization—create the oscillator and its wavetables as needed: control—change the oscillator frequency, and pulse width for PWM every sample: … Continue reading →

Posted in Digital Audio, Oscillators, Source Code, Wavetable Oscillators | Tagged | 27 Comments