difference between boost and gain of Medium EQ

wangea Question

Nov 7, 2024 00:00

Hello All,

I got one question with the parameters of Mid EQ filter. In the Wiki, the parametric gain is to set the overall gain while the parametric boost controlling the level of the filtered portion.

I made a test to check the difference, one filter :boost 0,gain 1; another one: boost 1,gain0; shown as below:

and i found the result was the same, but the parametric b0,b1,b2,a1,a2 is quite different, what is the calculation formula of these five parametric when boost is zero?

So I'm a little bit confused about the difference between boost and gain. And what does the overall gain and filtered portion mean? If i want change the response at the specific frequency, which parametric should i use ?

Thanks.

Eason

Audio Signal Processors

software

SigmaDSP Audio Processors

adau1701

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Harishgowtham Reply

Nov 7, 2024 00:00

Hello Eason,

The overall gain is just a gain applied to your overall signal just same as if your signal going thru a gain block set for particular value. Please refer the pictures below. You can see how the output changes according to the values set in the filter. The blue trace is the one which goes thru the filter and yellow goes thru the gain block.

In this below picture, you can there is no filtering, the B0 coefficient is 1 and rest are 0. which means the signal comes into the filter and multiplied by '1' and goes out (since the rest of the coefficients are 0, when they get summed, it will be the same value). You can see analog signal out for two paths.

In this below picture, I set the overall gain as -3dB. You can see in the param window that only B0 is updated as 0.707 (-3dB) and rest are zero. Here also the same thing, the signal comes in and get multiplied with 0.707 and goes out of the filter. since rest of the coefficients are zero, the final sum will be the same value. This is just like you set the gain block for -3dB (0.707 in linear)

In this below picture, I changed the boost value to -6dB. Here you can see the filter in action. All coefficients have their values, and the filter is applying the given gain (-6dB) to the particular frequency (500Hz). The -6dB is 0.5 in decimal, so you can see the output is just half of the 0dB.

In the below picture, I changed the input frequency to 1KHz, you can see there is a drop in the output due to the circled part in the image.

I hope this helps. I used the sigma3xx processor to do this, but the concept is just the same.

Regards,

Harish