Category Archives: Digital Audio

Sampling theory, the best explanation you’ve ever heard—Prologue

Posted on August 15, 2017 by Nigel Redmon

I’ve been working on a new video, with the goal of giving the best explanation of digital sampling you’ve ever heard. The catch is I started on it three years ago. I’m not that slow, it’s just that I’ve been … Continue reading →

Amp simulation oversampling

Posted on May 27, 2017 by Nigel Redmon

In tandem with our last article on Guitar amp simulation, this article gives a step by step view of the sampling and rate conversion processes, with a look at the frequency spectrum. From guitar to digital The first two charts embody the … Continue reading →

Posted in Digital Audio, Effects, Guitar Amp Simulation, Sample Rate Conversion | 4 Comments

Guitar amp simulation

Posted on May 26, 2017 by Nigel Redmon

In this article, I’ll sketch a basic guitar amp simulator. For one, questions on the topic come up often, and also, it will be a good example of a typical use of working at a higher sample rate. The most … Continue reading →

Posted in Aliasing, Digital Audio, Sample Rate Conversion | 3 Comments

About coefficient conventions

Posted on January 4, 2017 by Nigel Redmon

It’s been asked many times, so it’s worth an article explaining the conventions used on this site for transfer functions, and why they may differ from what you see elsewhere. People run into this most often with biquads: I use … Continue reading →

Posted in Biquads, IIR Filters | 7 Comments

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 | 13 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 | 32 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

Dither—The Naked Truth video

Posted on January 22, 2015 by Nigel Redmon

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