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Category Archives: Aliasing
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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A closer look at upsampling filters
Interpolation type: None Zero-order hold Linear Sinc 1 Sinc 2 Sinc 3 Show impulse response Sweep! In this demonstration, we generate a sine wave sweep from low in the audio band to near the Nyquist Frequency, which is half the … Continue reading
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, FIR Filters, Filters, Sample Rate Conversion
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What is aliasing?
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
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Oversampling
In this discussion, “oversampling” means oversampling on output—at the digital to analog conversion stage. There is also a technique for oversampling at the input (analog to digital) stage, but it is not nearly as interesting, and in fact is unrelated … Continue reading
Posted in Aliasing, Digital Audio, Sample Rate Conversion
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Digital audio: theory and reality
The promise of perfect audio—the Nyquist Theorem Most people who’ve look at digital audio before know about the Nyquist theorem—if you sample an analog signal at a rate of at least twice its highest frequency component, you can convert it … Continue reading
Posted in Aliasing, Digital Audio, Dither, Jitter, Phase
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