Author Archives: Nigel Redmon

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 | 25 Comments

Biquads

Posted on February 28, 2003 by Nigel Redmon

One of the most-used filter forms is the biquad. A biquad is a second order (two poles and two zeros) IIR filter. It is high enough order to be useful on its own, and—because of coefficient sensitivities in higher order … Continue reading →

Posted in Biquads, Digital Audio, Filters, IIR Filters | 34 Comments

Pole-Zero placement

Posted on February 27, 2003 by Nigel Redmon

Use the new, improved pole-zero calculator—but be sure to read the “Experiments with standard biquads” section below for tips on placing poles and zeros for standard filters. Here’s a Java applet that illustrates pole-zero placement. It lets you design a … Continue reading →

Posted in Biquads, Digital Audio, Filters, IIR Filters, Widgets | 8 Comments

A gentle introduction to the FFT

Posted on August 31, 2002 by Nigel Redmon

Some terms: The Fast Fourier Transform is an algorithm optimization of the DFT—Discrete Fourier Transform. The “discrete” part just means that it’s an adaptation of the Fourier Transform, a continuous process for the analog world, to make it suitable for … Continue reading →

Posted in Digital Audio, FFT | 11 Comments

A bit about reverb

Posted on January 19, 1997 by Nigel Redmon

Reverb is one of the most interesting aspects of digital signal processing effects for audio. It is a form of processing that is well-suited to digital processing, while being completely impractical with analog electronics. Because of this, digital signal processing … Continue reading →

Posted in Convolution, Digital Audio, Impulse Response, Reverb | 11 Comments

The Fourier series

Posted on November 14, 1996 by Nigel Redmon

(Java is no longer supported by many popular browsers, and can be difficult to enable others…) Experiment with harmonic (Fourier) synthesis with this Java applet! The sliders represent the levels of the first eight harmonics in the harmonic series. The second harmonic … Continue reading →

Posted in Digital Audio, FFT, Fourier, Widgets | 3 Comments

A question of phase

Posted on October 21, 1996 by Nigel Redmon

If you’ve paid attention for long enough, you’ve seen heated debate in online forums and letters to the editor in magazines. One side will claim that it has been proven that people can’t hear the effects of phase errors in … Continue reading →

Posted in Digital Audio, Phase | 5 Comments

The jitters

Posted on October 21, 1996 by Nigel Redmon

When samples are not output at their correct time relative to other samples, we have clocatz jitter and the associated distortion it causes. Fortunately, the current state of the art is very good for stable clocking, so this is not … Continue reading →

Posted in Digital Audio, Jitter | 2 Comments

What is aliasing?

Posted on October 20, 1996 by Nigel Redmon

It’s easiest to describe aliasing in terms of a visual sampling system we all know and love—movies. If you’ve ever watched a western and seen the wheel of a rolling wagon appear to be going backwards, you’ve witnessed aliasing. The … Continue reading →

Posted in Aliasing, Digital Audio | 16 Comments

What is dither?

Posted on October 20, 1996 by Nigel Redmon

To dither means to add noise to our audio signal. Yes, we add noise on purpose, and it is a good thing. How can adding noise be a good thing??!!! We add noise to make a trade. We trade a … Continue reading →

Posted in Digital Audio, Dither | 43 Comments