# Tag Info

Accepted

### 4th order high-pass filter on a DSP: standard or biquads?

The two solutions in a floating point implementation are assumed to be identical, with the two BiQuads being a factored version of the standard difference equation. The BiQuad is the better way to go ...
• 52.3k
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### Avoiding clicks with changing biquad coefficients

Another possibility is to send the coefficients as poles and zeros and interpolate/smooth in the z-plane instead of the coefficient domain. This is always guaranteed to be stable. You can either ...
• 45.5k

### Series vs Parallel Biquad Filters

It really depends on your filter. In my experience serial is has almost always the potential to be better. The reason for this is quite simple. The parallel representation is unique. There is one ...
• 45.5k
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### Prewarping both resonant frequency $f_0$ and bandwidth (or $Q$) when using bilinear transform

alright, there are a couple of different issues that may (or may not) need to be de-conflated. i'm gonna try to keep the number of symbols minimized. $dB_\text{gain}$ is the number of dB gain of the ...
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### Series vs Parallel Biquad Filters

Is this because of precision issues in fixed point?Is this still true for floating point schemes? Floating point has its own precision issues. Often a carefully-executed 32-bit fixed-point filter ...
• 12.9k
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### Is it possible to combine two or more Biquads?

Possible, yes. But higher-order IIR filters tend to be less stable and more susceptible to various numerical problems (lost precision, underflow, overflow, etc.), compared to a cascade or bank of ...
• 35.4k

### Avoiding clicks with changing biquad coefficients

I think the basic premise of your question is incorrect. Interpolating coefficients doesn't lead to unstable filters in biquads; moreover, it is very easy to prove. Just plot a1 vs a2 and you'll see ...

### How to calculate biquad coefficients for the partial (1%, 10%) applying of pre-emphasis effect

I have too few points for to comment so I try give you at least a partial answer. You can't change those b coefficients using equal multiplier with a's. As those final coefficients comes from ...
• 917
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### What's the point of MATLAB's scaling array for secord-order-section filters?

Of course an SOS matrix is capable of completely describing the filter including the gain. However, in the Matlab SOS matrix the $b_0$ coefficients are all equal to $1$ by default (if no extra scaling ...
• 90.5k
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### How do scaling of the coefficients for the poles of a biquad filter affect the gain?

Sorry, that doesn't work. You have to scale all numerator (the "b") or all denominator coefficients (the "a") at the same time. That doesn't work for the denominator since you all practical ...
• 45.5k

Taken from this excellent RDS tutorial, and original source: De-emphasis filter, $H(s) = \frac {1} {RC.s + 1}$, implemented as IIR filter via a bilinear transform: ...
• 463

You could also implement a 2nd order IIR filter which has response of 1st order filter by using some other TF but one used in RBJ's cookbook. Here's one way to do it using MZT (C++). ...
• 917

### How to calculate biquad coefficients for the partial (1%, 10%) applying of pre-emphasis effect

So, sox defines its biquad operation parameters as follows: biquad b0 b1 b2 a0 a1 a2 Apply a biquad IIR filter with the ...
• 31.2k
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### Why does my low pass filter diverge below 7000 Hz?

Let's try this in Octave/Matlab: a = [1,-1.601089848140876,0.668366341586459]; b = [0.016819123361395717,0.033638246722791434,0.016819123361395717]; r = roots(a); abs(r) ans = 0.81754 0.81754 ...
• 90.5k

### IIR biquad real-time filter just output noises

It looks like you got your a and b coefficients swapped. The feedback terms: b0,b1,b2, should be tiny (around 0.00x), and a0,a1,a2 can be close to 1 or 2 in magnitude.
• 35.4k
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### IIR biquad real-time filter just output noises

I was unable to get a stable filter using your coefficients. You did not state, but am assuming this is a lowpass filter. Using the calculator here, I got: ...
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### Biquad filter from Matlab to C using "tf2sos"

What I can see from the code is the following mapping between the array coeffs[] and the filter coefficients $a_i$ and $b_i$ (note that $a_0=1$ and is not stored in ...
• 90.5k

### Avoiding clicks with changing biquad coefficients

You could limit the rate of sending a change of coefficients to that of the cross fade duration. But send the latest setting at each duration tick (every 16 mS video frame or equivalent, for instance)...
• 35.4k

### Avoiding clicks with changing biquad coefficients

The reason why interpolating the coefficients would cause instability is that intermedite set of coefficients values could potentially produce poles outside the unit circle, thus making your filter ...
• 754
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### Help with audio EQ cookbook BPF filters and Q

i believe that what you're seeing is the compression of bandwidth done by the frequency warping inherent with the bilinear transform. now, if you look at cookbook, the bandwidth $BW$ is expressed in ...
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### Can a Goertzel filter response be mapped to a Direct Form II Biquad IIR Filter

try it, you'll like it. the form in the Jocobson & Lyons paper is Direct Form II, with the coefficients explicit. the form in the CMSIS source is a transpose of a Direct Form I, i believe, and ...
Consider a discrete-time LTI system (that's your second order stage) described by a LCCDE in the form of a recursion equation: $$y[n] = a y[n-1] + b y[n-2] + c x[n] + d x[n-1]$$ where $a,b,c,d$ are ...