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Category Archives: Aliasing
A wavetable oscillator—Part 2
From Part 1, we have an oscillator. But we need to broaden it to allow scaling of harmonic content based on pitch so that we have all the harmonic content we need at the low frequency end, and, as we … Continue reading
Posted in Aliasing, Digital Audio, Oscillators, Wavetable Oscillators
11 Comments
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, Filters, FIR Filters, Sample Rate Conversion
4 Comments
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
8 Comments
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
3 Comments
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
6 Comments