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Category Archives: Digital Audio
Towards practical resampling
In a previous article, we looked at sample rate conversion in the frequency domain. Let’s take a quick second look in the time domain as reinforcement of principles behind sample rate conversion, before developing a practical rate convertor. In an … Continue reading
The sound of dither
Dithering is about spreading errors out, so that they aren’t related to the sampled signal. A constant background hiss is easier to ignore than tones that change depending on signal frequencies and amplitude. Here’s a fixed-frequency sine wave, truncated to … Continue reading
Posted in Digital Audio, Dither
7 Comments
Sample rate conversion
Here we explain how sample rate conversion works. As an essential prerequisite, you must understand the principals of sampling. Even if you understand sampling already, read our explanation of the process here. The viewpoint and terms used there are mirrored … Continue reading
Posted in Digital Audio, Sample Rate Conversion
16 Comments
Sampling in-depth
Here we lay the foundation. We’ll look at analog to digital conversion, and we’ll look at the spectrum of the resulting digital signal. We’ll use that knowledge to help understand the conversion process back to analog. Though we can build … Continue reading
Posted in Digital Audio, Sampling Theory
2 Comments
The bilinear z transform
The bilinear transform is the most popular method of converting analog filter prototypes in the s domain to the z domain so we can implement them as digital filters. The reason we are interested in these s domain filters is … Continue reading
Posted in Digital Audio, Filters, IIR Filters
29 Comments
The digital state variable filter
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
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
A gentle introduction to the FFT
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
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