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View Full Version : Shelf filter support for biquad



Ben
07-19-2016, 12:34 AM
Hi,

I added support to configure biquad stages with shelving filter response: Link to GitHub (https://github.com/Ben-Rheinland/Audio/commit/e8783ef6b87c50e448be819c1a89e68ff129dbed).

The functions are
setLowShelf(stage, frequency, gain, slope);
and
setHighShelf(stage, frequency, gain, slope);

This picture describes what is what:
7680
The frequency describes the slopes midpoint, the amplitude at this point is always (gain/2), independent of the slope parameter.
Gain is specified in dB and can be positive or negative.
The slope parameter configures how steep the change in amplitude will be, gain=1 is maximum steepness without overshoot/undershoot in the frequency response. gain < 1 is a less steep curve, gains > 1 have even steeper transitions at the specified frequency at the cost of over-/undershoot.

Ben

Ben
07-19-2016, 02:38 PM
I added documentation to the Design Tool (GUI): Link (https://github.com/Ben-Rheinland/Audio/commit/d16055bfbd6dd92fbb751663d5b9a5a0cb61854c)
I tested both low and high shelf filters with various frequencies, gains and slopes and checked with the FFT function of my oscilloscope. The filters work as intended.

steven32bits
10-13-2016, 07:27 AM
Is it possible to add gain to the band pass or notch filters?

steven32bits
10-14-2016, 05:49 AM
Hi Ben,

I decided to run each filter into another mixer and use the gain functions of the mixer. This is certainly not easy with a simple gain input of 1 to 1dB. I am curious is there documentation on the transfer function for the bandpass and notch/band stop filters?

steven32bits
10-14-2016, 11:04 PM
Is there documentation on the transfer function for the bandpass and notch/band stop filters?