Monthly Archives: December 2010

A biquad calculator

Posted on December 20, 2010 by Nigel Redmon

Something useful: a biquad filter coefficient calculator… Continue reading →

Posted in Biquads, Digital Audio, Filters, IIR Filters | 11 Comments

Sample rate conversion: down

Posted on December 20, 2010 by Nigel Redmon

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 | Leave a comment

A closer look at upsampling filters

Posted on December 11, 2010 by Nigel Redmon

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 →

Posted in Aliasing, Digital Audio, Filters, FIR Filters, Impulse Response, Sample Rate Conversion | Leave a comment

Sample rate conversion: up

Posted on December 5, 2010 by Nigel Redmon

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

Building a windowed sinc filter

Posted on December 5, 2010 by Nigel Redmon

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 →

Posted in Digital Audio, Filters, FIR Filters, Impulse Response, Sample Rate Conversion | 2 Comments