# Tag Info

Accepted

### Filter Order Rule of Thumb

My favorite "Rule of thumb" for the order of a low-pass FIR filter is the "fred harris rule of thumb": $$N=\frac{f_s}{\Delta f}\cdot\frac{\rm atten_{dB}}{22}$$ where $\Delta f$ ...
• 50.3k
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• 89.5k
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### Meaning of Phase response of a filter? In simple words?

There are many good answers here. I will try to take the reverse approach in order to explain in very simple words what is necessary in order to keep the output's shape same as input's, and what ...
• 2,611
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### Why can't realisable IIR filters have linear phase?

The frequency response of a real-valued discrete-time system with linear phase has the form $$H(e^{j\omega})=A(\omega)e^{-j\omega\tau},\qquad\omega\in [-\pi,\pi]\tag{1}$$ where $A(\omega)$ is either ...
• 89.5k
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### How do software equalizers work?

This depends a lot on how you implement it. A single biquad takes about 10 arithmetic operations. (To be precise a Transposed Form II takes 4-5 multiplies and 3 adds, depending on how the gain ...
• 44.1k
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### How does this "simple filter" work?

In more standard DSP terms, you have the following filter: $$y[n] = (1-a) x[n] + a y[n-1]$$ where $x[n]$ and $y[n]$ are the input and output signals at time $n$ respectively. The transfer ...
• 5,016
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### 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 ...
• 50.3k
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### Design a linear-phase FIR filter approximating the magnitude of a given IIR filter

What you do in step 1 is simply truncate the infinite impulse response to approximate it by an FIR filter. If you use sufficiently many filter taps, the approximation becomes arbitrarily accurate. ...
• 89.5k
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• 1,420

### Frequency Domain Filtering

This is just "faking" the magnitude response of an IIR filter. The output's magnitude spectrum looks just like it has been filtered by the IIR filter with the given frequency response. Although it may ...
• 4,255
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### Advancing a causal IIR filter's impulse response

Let's consider a causal IIR filter with the following transfer function: $$H(z)=\frac{B(z)}{A(z)}=\frac{\displaystyle\sum_{n=0}^{M}b[n]z^{-n}}{1+\displaystyle\sum_{n=1}^{N}a[n]z^{-n}}\tag{1}$$ Note ...
• 89.5k
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### Protect an IIR filter from being reverse-engineered

Short answer: You can't. If an attacker can insert a signal that covers the whole bandwidth (e.g. a white signal, or at least one that has no spectral zeros) into the system (and he can do that over ...
• 30.2k