[music-dsp] Newbie Q: how to implement a real-time high freq remover?

[Lance Boyle]

Google digital filter design interactive

The top hit looks wonderful.

Jerry

On Feb 1, 2005, at 12:25 AM, Qiangning Hong wrote:

> I am developing a real-time recording application.  I am only 
> interested in signal below 6KHz so I want to apply a low-pass filter 
> on the input.  As I know little about DSP, I copied the following 
> filter from internet:
>
> y(n) = x(n) * a0 + x(n-1) * a1 + y(n-1) * b1
>
> with:
>    w = 2 * framerate
>    cutoff = 6000 * 2 * PI
>    norm = 1 / (cutoff + w)
>    b1 = (w - cutoff) * norm
>    a0 = a1 = cutoff * norm
>
> It works but the output is not ideal.  The signal above 6KHz is still 
> too high and the output sounds a bit different with the original one.
>
> Can anyone point me to a correct way?
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