Downsampling and applying a lowpass filter to digital audio

Question

I\'ve got a 44Khz audio stream from a CD, represented as an array of 16 bit PCM samples. I\'d like to cut it down to an 11KHz stream. How do I do that? From my days of engine

Answer 1

The process you're after called "Decimation". There are 2 steps:

1. Applying Low Pass Filter on the data (In your case LPF with Cut Off at Pi / 4).
2. Downsampling (In you case taking 1 out of 4 samples).

There are many methods to design and apply the Low Pass Filter.

You may start here:

http://en.wikipedia.org/wiki/Filter_design