This code is also dangerous "LGPL" :-)

Seriously, I'm afraid this is also too much for him. Code is not really good to explain solutions. I prefer the clarification and let people code themselves.

Let's try it this way:

1. Apply an anti aliasing filter with an edge frequency of about 2..3kHz and a stop frequency of not more than 4kHz to meet the 8kHz sampling rate. Do not use only linear interpolation but CIC + FIR. For simple approaches use an IIR. A nice filter was a 6x4 TAP FIR Filter and a 3kHz edge.

2. Pick up every 6th sample to get 8kHz

3. Appreciate a dark sound without any "s", "t" ... :-)

To transform back to 48kHz

1. use a linear interpolation with a one stage CIC. Do not use the often proposed filling with zeros. For simple solutions use the smaple 6 times.

2. Apply a short 12 TAP - FIR filter with an edge frequency of 16kHz which has easy coefficients for 48kHz and reduces artifacts from the linear interpolation.

3. This should maintain the 8kHz quality without new degradation


Am 23.07.2018 um 03:08 schrieb Henrik G. Sundt:
This solution, without using any low pass filters before and after the desimation, will generate a lot of aliasing frequencies, Kjetil!

Here is another solution:


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