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Author Archives: Nigel Redmon
Sample rate conversion: down
In doubling the sample rate, we inserted zeros between existing samples, then used a lowpass filter to remove the resulting alias in the audio band. To resample at half the current rate, we use a lowpass filter to remove audio … Continue reading
Posted in Aliasing, Digital Audio, Filters, Sample Rate Conversion
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Sample rate conversion: up
Once we have a suitable set of FIR filter coefficients from our windowed sinc calculator, it’s time to apply them. Again, our recipe for doubling the sample rate: 1) Insert a zero between existing samples. (This is the upsampling step, … Continue reading
Posted in Aliasing, Convolution, Digital Audio, Filters, FIR Filters, Sample Rate Conversion
7 Comments
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
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
3 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
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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
29 Comments