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Questions tagged [biquad]

Biquad is referred to either analog or digital second order filters

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3 votes
2 answers
285 views

First order filters in Direct Form I (RBJ Cookbook)

I've implemented second order biquad filters using the famous RBJ Cookbook. I also want to implement first order lowpass and highpass filters. I was hoping to use the same code, so I need to define ...
0 votes
1 answer
574 views

Two question about RBJ Peak filter

I'm new into DSP and Filters in general. Its the first step ahead I do from learning and using a 1-pole IIR basic Low Pass Filter. I'm about to implement for my VST audio application (using C++ and ...
5 votes
1 answer
184 views

"Tone Control" IIR filter coefficients

The documentation for Analog Device's sigmastudio shows some of the formulas behind their biquad IIR filter coefficients. The usual suspects (HP, LP, peaking, ...) as described in RBJ's cookbook are ...
2 votes
2 answers
285 views

What is the $Q$ of successive Second-Order Sections of an $N$th-order Butterworth low-pass filter?

What if you had an $N$th-order Butterworth lowpass filter filter with -3 dB frequency of $\Omega_0$? $$ \Big| H(j\Omega) \Big|^2 = \frac{1}{1 + \left(\frac{\Omega}{\Omega_0}\right)^{2N}} $$ The number ...
3 votes
1 answer
127 views

Audio EQ Cookbook Stability

I'm implementing 6 cascaded biquad peaking filters to make a 6-band EQ. In the system I want to calculate the coefficients on the fly (it's just gain thats changing, center frequency and BW aren't). I ...
2 votes
1 answer
85 views

low shelving filter frequency response diagnosis

I am building a second order modified biquad filter based on an implementation by Will Pirkle in "designing audio effect plugins in c++". However when I look at my implementation's ...
2 votes
3 answers
438 views

Series vs Parallel Biquad Filters

What are the pros and cons of arranging a set of biquad filters in series and parallel? I gather that series should be used in cases where the filters contribute to the same passbands and vice versa ...
1 vote
1 answer
66 views

How to specify the cut-off frequence in cascaded biquad filters?

As part of my effort to understand how a high-pass filter can be implemented, I'm reading this section of HandWiki. My question here is: How do the 2 simple formula presented there filter out at a cut-...
1 vote
1 answer
81 views

Understanding how to implement high-pass filter with cascaded biquad filters

I'm trying to understand how to implement a high-pass filter using, quote: a cascasded biquad direct form II IIR filter with a cut-off of 8kHz. DSP is a complete new field for me, and the ...
2 votes
0 answers
60 views

How do I obtain narrowband reverberation times in the bass range to detect room modes?

I calculate my impulse response according to this principle. Calculating the inverse filter for the (exponential) sine sweep Method. With the obtained impulse response I calculate my reverberation ...
6 votes
1 answer
282 views

Pole Quantization Patterns in 2nd Order IIR Resonators

Background My typical approach to fixed point design for digital filters is to iteratively scale and increase quantization while comparing the fixed point simulation to the floating point design ...
1 vote
1 answer
98 views

How to match coefficients of a SVF compared to Biquad in order to Plot the frequency response?

I'd like to output the frequency response of this filter. Here's how the coefficients are calculated: ...
0 votes
1 answer
107 views

BPF design as cascaded second order biquads

I am trying to design a bandpass filter in MATLAB with following specs: $$\texttt{f_s = 20000Hz}$$ $$\texttt{3dB freq = [392 464]Hz}$$ $$\texttt{filter order = 8}$$ When I tried to implement the ...
2 votes
2 answers
846 views

Biquad cookbook formula for broadcast FM de-emphasis?

Can a simple IIR biquad filter be used as an audio de-emphasis filter for broadcast FM radio? If so, how does one translate the filter requirements (50 uS time constant in the U.S.?) into parameters ...
1 vote
3 answers
1k views

How do you calculate the group delay in samples of a Biquad Filter at a given frequency from the coefficients?

If I have a BiQuad all-pass filter with a given set of coefficients such as: g: 0.903228 a1: -1.88142 a2: 0.903228 B1: -2.08299 B2: 1.10714 And my operation per ...
0 votes
1 answer
179 views

design of cascaded biquad filter

I have to compare the response of an 8th order IIR filter and its equivalent 4 stage cascaded biquad structure. A sinusoidal signal is given as input to both the systems and the output responses are ...
1 vote
0 answers
49 views

Is it possible to lower the slope of a biquad lowpass? [duplicate]

I'd like to implement a lowpass with arbitrary slope. I'm currently cascading biquads in order to get a higher order, hence higher slope. But is it possible to do the opposite - lower the slope of one ...
1 vote
1 answer
209 views

using scipy.signal.sosfilt to filter a stereo signal with zi, zf

I'm stuck trying to filter a two-channel signal using sosfilt() with the zi initial state. I need to use the zi parameter so I can carry the filter state over ...
1 vote
2 answers
923 views

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

I'm using sox to emulate RIAA pre-emphasis and de-emphasis effects on audio files. For pre-emphasis I call it like this: ...
1 vote
1 answer
467 views

How to calculate IIR Lattice Filter Coefficients for Biquad Filter

If I have a biquad filter with known $a_1, a_2, b_0, b_1, b_2$ coefficients, how do I calculate the corresponding lattice/ladder coefficients? I have found information on deriving the lattice ...
9 votes
1 answer
7k views

Plotting the magnitude response of a biquad filter

I've put together a multi-band audio EQ using biquad filters. I'm getting the coefficients using the methods from the RBJ cookbook. Now I want to plot the curve showing the magnitude response. I'm ...
1 vote
3 answers
549 views

Biquad cascading frequency response

I am implementing EQ lines in my filter. I need to do biquad with slope 24 db/oct, 36/oct and bigger so I would like to cascade several biquads. I am stuck with calculating frequency response of two ...
2 votes
2 answers
174 views

What procedure to find the parameters of a given filter prototype to fit a desired frequency response?

To model the frequency response of a system, I am looking for a method to fit the response of cascaded bi-quad filters to the response of that system using an optimization algorithm. The $S$-domain ...
1 vote
1 answer
443 views

Biquad coefficients using Magnitude (or Phase) Invariance Mapping Method

I'm trying MIM (Magnitude Invariance Method) and PIM (Phase Invariance Method) for to improve biquad LPF response at low sampling rates. I'm looking some help and examples of usage if available. ...
2 votes
2 answers
2k views

How to implement cascaded biquad transfer functions in Python/SciPy

I am trying to implement in python/Scipy the biquad filter with the following S-domain transfer function: $$ H(s)=\frac{w_0^{2N-1}(s+w_z)}{[s^2+(w_0/Q)s+w_0^2]^N} $$ My problem here is that because of ...
0 votes
0 answers
286 views

Discrepancy in frequency response of biquad filter (in Python)

I have written a simple biquad filter class but when I check its frequency response, I get different results with different methods. If I check it "empirically" (by taking the FFT of its ...
3 votes
3 answers
628 views

ELI5: How do biquad filters like bandpass "know" the frequency of a signal?

I understand the code behind biquads, but I fail to understand how 5 coefficients in a biquadratic formula can isolate frequencies so precisely, especially considering it only takes the last two ...
2 votes
1 answer
1k views

Prewarping both resonant frequency $f_0$ and bandwidth (or $Q$) when using bilinear transform

RBJ's Audio EQ cookbook takes into account only frequency prewarping when case Q is used for bandwidth. Why not $Q$ prewarping as well with some of those filter ...
0 votes
1 answer
585 views

Biquad high-pass filter not working as expected

I'm trying to implement a high-pass filter using the the coefficients described in RBJ's well-known EQ cookbook (see https://www.w3.org/TR/audio-eq-cookbook/). However, when I run white noise through ...
0 votes
1 answer
105 views

Biquad Filter Non-Linearity

I'm using a biquad filter algorithm in my project. I got 3, 16 size variable arrays summing into one and then gets filtered. Now i want to filter each array seperately and sum after that, which if the ...
0 votes
0 answers
166 views

Biquad Type-II Coefficient Generation

I have a Biquad II filter implementation in my embedded environment and I'm trying to find some equations to generate the coefficients for it. I have already found the Audio Eq Cookbook, which simply ...
1 vote
2 answers
1k views

Help with audio EQ cookbook BPF filters and Q

I am fairly new DSP, and am using maths that I have not used in 20-30 years. I have been working with Cookbook formulae for audio EQ biquad filter coefficients by Robert Bristow-Johnson and am having ...
1 vote
2 answers
925 views

Regarding BIQUAD IIR implementation in MATLAB

I want to implement a high pass filter (order 4) in MATLAB using cascade form. ...
1 vote
0 answers
145 views

High pass biquad cascade transposed direct form II low frequency accuracy

I'm quite new to DSP and I'm trying to implement high pass biquad cascade in transposed direct form II. Currently my implementation has very poor accuracy at cutoff frequencies that are less than 5kHz ...
3 votes
4 answers
2k views

Avoiding clicks with changing biquad coefficients

I have a DSP application that filters a signal with five cascaded biquads whose coefficients are determined by the Audio EQ Cookbook formulae (Thanks for this work, Mr. Bristow-Johnson btw). Each ...
2 votes
1 answer
573 views

How to optimally normalize filter coefficients?

I have designed an IIR filter in Matlab that comprises the following biquads ...
0 votes
1 answer
99 views

Derive Time-Domain Biquad Coefficients from Z-Domain

I'm trying to derive the time-domain coefficients of a biquad filter based on its z-domain coefficients. The purpose is to import externally-generated EQ filters (in z-domain) into Max/MSP (in time-...
1 vote
1 answer
99 views

bibliography about implementation of IIR filters

I need to implement a 6th order IIR filter. The filter I need to implement is the A-weighting. I've simply used the bilinear function of Matlab with an fs of 20Khz. I need to implement this over the ...
0 votes
1 answer
400 views

Direct form 1 filter equation for a biquad filter

In general, we all know that the direct form 1 equation for a biquad filter is given by $$y(n) = b_0x(n) + b_1x(n-1) + b_2x(n-2) - a_1y(n-1) - a_2y(n-2)$$ But when it comes to practical applications ...
1 vote
2 answers
761 views

Converting cascaded biquads to parallel biquads

I need to convert a fourth-order IIR filter made using two cascaded second-order sections with the transfer function: $$ H(z) = \frac{b2_{1}z^{-2} + b1_{1}z^{-1} + b0_{1}}{a2_{1}z^{-2} + a1_{1}z^{-1} ...
8 votes
1 answer
4k views

Realtime fixed point IIR filter implementation in C

I would like to implement a fourth order fixed point low-pass IIR filter in C (with Q15 arithmetic), and I will prepare this filter by using two stages cascaded direct form-II bi-quad filters. I have ...
0 votes
2 answers
1k views

Calculating the true values of biquad filter coefficients from normalized form

I have a C code in which the IIR filter(BiQuad) uses only 4 (normalized) coefficients per stage (a2/a0,a1/a0,b2/b0,b1/b0) instead of 6 coefficients (a0,a1,a2,b0,b1,b2). I know that the value of a0 is ...
0 votes
2 answers
135 views

IIR Cascaded Filter Response, Unexpected Results

I am attempting to understand how to manipulate portions of a cascaded series of biquad notch filters in a control system I am working with. As part of determining the composite response of all the ...
9 votes
3 answers
5k views

Why Is Bi Quadratic Interpolation for Image Resampling / Interpolation Rarely Done?

Related question: What are the practically relevant differences between various image resampling methods? Bilinear and bicubic interpolation for image resampling seem to be fairly common, but ...
3 votes
1 answer
5k views

Design a Filter with Resonance

I want to design a Filter with a variable Cutoff Frequency and Resonance. However in the source I'm using there is a Bi-Quad Filter with two IIR and two FIR Filters designed like this : Furthermore ...
0 votes
1 answer
281 views

Why does my low pass filter diverge below 7000 Hz?

I'm trying to create a LPF, using language JAVA. My first aim is to understand how filters design is working and the second one is to create a "home made" equalizer with "home made" filters. To help ...
0 votes
1 answer
132 views

Known problems with IIR DF2 when using 64-bit floating point processing?

So far I was using DF1 for biquad filters for audio DSP, but it turns out that it is possible to gain significant performance gains using the new AVX/AVX512 instruction sets using DF2. Are there any ...
2 votes
1 answer
285 views

Biquad and polarity flipping

Assuming normalized biquad coefficients: $$ H(z) = \frac{b_0 + b_1z^{-1} + b_2z^{-2}} {1 + a_1z^{-1} + a_2z^{-2}} $$ And taking the definition of flipping the polarity as multiplying every tap in a ...
1 vote
0 answers
250 views

Issue with the Massberg Analog-Matched Low Pass Filter

Implemented the filter mentioned in title using Octave and couple sources Vicanek and Zeitlin (LPF.cpp). Got filter working otherwise but, ... when tested the responses against 'analog model' of the ...
2 votes
1 answer
765 views

How would I calculate the state-variables of digital biquad filter (direct form II transposed) at steady-state?

I'm attempting to calculate the steady-state state variables for a digital biquad filter direct form II (transposed). Illustration For example, let assume the filter is fed a constant input of ...