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Author Archives: Nigel Redmon
Building a windowed sinc filter
As promised, here’s our windowed sinc calculator for building a 2x oversampling filter: Factor Length Rejection Gain Notes: Use the Tab or Enter keys to effect changes (most browsers), or press Calculate. The frequency axis is in multiples of the … Continue reading
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
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Blog birth
Sometimes I get email asking a question—a question that I think others might have. Sometimes I’d like to write some helpful notes, but maybe it doesn’t warrant a full article. Or sometimes I’d like to address a subject in pieces. … Continue reading
Posted in Uncategorized
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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
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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
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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
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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
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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 Digital Audio, Filters, IIR Filters
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Pole-Zero placement
Here’s a Java applet that illustrates pole-zero placement. It lets you design a filter with two poles and two zeros, while showing the resulting frequency response and filter coefficients. It’s also handy for learning more about how poles and zeros … Continue reading
Posted in Digital Audio, Filters, IIR Filters
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