Questions tagged [digital-filter]

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15
votes
3answers
9k views

Why should I use digital filters for bandpassing rather than simply manipulate signals in frequency domain and then recover them into time domain?

I'm quite a novice for signal processing and I know this question may be too broad. But I would still like to hear hints from experts. I was taught to use butter (...
13
votes
6answers
2k views

Extremely low frequency filters

I have a data acquisition board(A/D+Digital Signal Processor) and I want to check if a digital high-pass filter(implemented in DSP) at an extremely low cut-off frequency(0.05Hz) is actually working. ...
12
votes
3answers
8k views

Why too many capacitors in parallel for Vdd supply net? Can't we just add all to replace with one big capacitor?

Here is a schematic of a Basys-2 board's power regulator IC and filters. It is just an example but this is fairly similar to many designs I've seen. Why are there so many capacitors added in parallel ...
7
votes
4answers
7k views

Performing FFT at low frequencies but high resolution?

To put this in context, I'm looking to achieve both high speed and high accuracy for measuring biosignals through the FFT. I'll describe a quick example to see if I understand this properly as well as ...
5
votes
3answers
7k views

Fastest moving averaging techniques with minimum footprint

I have tried few running averaging techs for smoothing the change in ADC data in AtMega48 for controlling lights(PWM) when rotating a pot(ADC). The filters (pseudo codes): Moving average: ...
5
votes
3answers
2k views

What are the origins of the window functions in DSP? Why not just use a rectangular window?

As far as I know, in DSP we wish to remove or reduce the effect of some undesired signals by separating its frequency spectrum from the spectrum of the whole signal (our main signal and the noise). ...
4
votes
1answer
196 views

What reduced the noise when multiplying neighbor samples?

Is this a common filtering technique? I multiplied each sample with it's neighbor. I was trying to distinguish the spikes from the noise. Low-pass filtering wasn't as helpful maybe because both the ...
4
votes
1answer
386 views

digital bandpass filter with parallel inputs

I have a high speed ADC connected to an FPGA. The ADC is designed such that you get 16 samples every FPGA clock cycle (that's samples, not bits). The 16 samples are from a single ADC input channel, ...
4
votes
1answer
159 views

Bireciprocal lattice wave digital filter

I am trying to model a bireciprocal Cauer filter in LTspice but I don't get the expected results. More precisely, using \$\gamma = \frac{re(p_i)-1}{re(p_i)+1} \$ where \$re(p_i)\$ is the realpart of ...
3
votes
3answers
9k views

Why is Direct Form 2 (Digital Filters) equivalent to Direct Form 1

According to Wikipedia : The alternate Direct Form II only needs N delay units, where N is the order of the filter – potentially half as much as Direct Form I. This structure is obtained by reversing ...
3
votes
2answers
2k views

Relationship between order of filter and impulse response?

I see that the slope of the frequency response of a filter (such as the Elliptic, Butterworth...) becomes steeper as its order increases; for instance, a low pass Elliptic filter with an order of N=3 ...
3
votes
2answers
274 views

Dedicated digital filter

I have built a DDS (0-80MHz) with an FPGA (XC3S400) that I can program it for making almost any wave form (limited frequency by the wave form complexity). After weeks of struggling with making a ...
3
votes
1answer
454 views

How is noise reduced using a sigma-delta converter?

Perhaps I'm sleepy but I can't quite get my head around how a sigma delta converter takes the noise that is in a bandwidth of (X) Hz and by over sampling spread, that same amount of noise over 2(X)Hz. ...
3
votes
1answer
110 views

Understanding digital filters, specifically their effects on time domain information, how to preserve the waveform of a signal being filtered?

According to Steven W. Smith, in his book: The Scientist and Engineer's Guide to Digital Signal Processing, when designing a digital filter, "Good performance in the time domain results in poor ...
3
votes
4answers
2k views

Do digital Anti Aliasing filters exist for traditional ADCs?

I'm currently learning about Analogue to Digital Converters. From what I understand, aliasing occurs if the input signal being sampled has power above the "Nyquist frequency" of the ADC(Sampling ...
3
votes
2answers
1k views

Magnetometer tilt compensation without accelerometer

I need to use the magnetometer in a device to accurately determine how many degrees the user twists (rotates in x-y plane) it. I don't care about absolute orientation, just the angular delta. Of ...
2
votes
4answers
1k views

Remove spikes from Load Cell readings

I have developed load indicator interfaced with load cell to display the value of load. The device is to be used in on-line weighing of a bag that is moving over the conveyor. Due to the mechanical ...
2
votes
4answers
2k views

Advantages of filtering signals using analog or digital methods?

In my understanding, it seems that there are, broadly speaking, two primary ways in which signals are filtered for analysis by computers, which are software-side filters and hardware-side filters (...
2
votes
3answers
923 views

SNR improvement from placing analog filter ahead of digital filter

We have designed a PCB containing a data collection circuit for a customer, and their external expert presents this "helpful suggestion": Question about signal averaging vs. longer integration ...
2
votes
3answers
705 views

Linear Phase Response

In many cases it is demanded that the filter has a linear phase response. (like in case of FIR ). Why linear is so important? Why not constant or anything else(any other shape)?
2
votes
1answer
39 views

LM567 or Custom bandpass filter

I'm using a array of hydrophones to localize an underwater pinger (37.5 kHz and 45 kHz) and I'm thinking of using LM567 tone decoder as a frequency filter. The other option is to design a custom ...
2
votes
1answer
479 views

DSP/dsPIC Getting Started

I am a last class eee student and I started to study on digital filters. I want to design a 0-150 Hz band pass filter for getting started(I have not determined certain parameters, I want to do ...
2
votes
1answer
521 views

Low pass Filter on an Analog Signal

I havent had much experience with low pass filters but,I do understand what they do. I was implementing one on an AC signal above. This is a sampled input, and I dont see how would you call the ...
2
votes
1answer
673 views

Low Pass IIR filter attenuating all frequencies

I am trying to make a Low pass IIR filter in dsPIC(dsPIC33FJ12MC202) using mikroC compiler. I have generated filter coefficients using Filter Design Tool. My filter specifications are as follows: LPF, ...
2
votes
2answers
1k views

Is Kalman filter suitable for smoothing sound spectrum?

I'm implementing a software similar to a real-time spectrograph with a modified FFT. The output vector summarizes the intensities of various musical tones present in the input signal. Its size is a ...
2
votes
0answers
269 views

RC filter - compute output as a function of input for generating waveform

I'm not so deeply into the theory about all this, I may use strange terminology... If I put a square wave through a simple lowpass RC filter, the output will be a sort of "rounded sawtooth", well not ...
1
vote
1answer
800 views

Using a Kalman filter requires a truth value?

I have some accelerometer data that I need to filter and clean. However, based on the online examples that I see, the filter requires what's called a "Truth value". The code is based on this: http://...
1
vote
1answer
240 views

Distinguishing between FIR and IIR filters from transform function

I was good at this but unfortunately I have forgot almost everything... So the question is what are the steps to tell if a transform function is for IIR or FIR filter: $$H(z) = \frac{z^3+5z^2+3z+1}{...
1
vote
1answer
601 views

FIR Filter 16-Bit

I am trying to implement a 32-tap filter on an FPGA, I can have only 16-bits for the coefficients, and 16bits for the input samples, and my output should also be 16 bits. Multiplying a 16bit ...
1
vote
3answers
507 views

Physical significance of group delay

What is the physical significance of the group delay of a system/filter?. Why is the slope of the phase response critical in a communication system.
1
vote
3answers
168 views

Sharp and Simple Analog Filter suggestions

I'm looking for schematics of some simple opamp-based analog filter, which has a sharp band-pass functionality. I want it to control small robot with sounds of different pitch. The matter is like ...
1
vote
3answers
9k views

Time delay: digital low pass filter VS analog low pass filter

I am new on digital filter, hopefully I can get some intuitive insights here. So, here is the question: A low pass filter with 5Hz cut-off frequency is to be designed. The signals presented have ...
1
vote
1answer
407 views

What is digital Termination and when is it used?

I have heard transmission line termination but today I came across this "Digital termination" but couldn't find out why is it used and what effect does it have on digital signals?
1
vote
2answers
112 views

predicting the charcteristics of Filters

I would like to know one thing that say if you know Processor word length(TMS320VC5510 DSP) it accumulator and guard bits can you make a guess about filter characteristics to be used for this ...
1
vote
1answer
237 views

Problems with implementation of a band-stop filter on an MCU (dsPIC) using fixed-point arithmetic

I'm trying to implement a band-stop (notch) filter on a microcontroller dsPIC33EP64GS506 to filter out a 100 Hz component from ...
1
vote
1answer
384 views

Digital filter implementation in C (embedded)

I am a recent grad and my new project at work deals with taking the signal from an electret microphone and getting SPL values for 10 standard frequency bands. The analog amplification/conditioning is ...
1
vote
1answer
96 views

Finding the system function of a digital filter

I am studying for exams and I need help with a question I came across in a textbook. Given a digital filter $$y_n = a(x_{n-1} + x_{n+1}) + bx_n$$ find the system function of this filter and the ...
1
vote
1answer
222 views

Group delay when using a matched filter

Supposing I have a discrete time signal x(n). when I pass this through an FIR filter h(n), and again pass this result through h(n) again (essentially this is a second order filtering), the group delay ...
1
vote
1answer
1k views

Is it possible to compute delay with an IIR filter between peaks?

I am developing a project which receives accelerometer signals as input, which must then be analysed via peak-detection algorithms (among other techniques). In order to do so more effectively, I ...
1
vote
1answer
39 views

Xilinx FIR filter behavior

We're currently simulating some Xilinx AXI Stream Finite Impulse Response (FIR) IP cores. https://www.xilinx.com/support/documentation/ip_documentation/fir_compiler/v7_2/pg149-fir-compiler.pdf The ...
1
vote
0answers
298 views

FIR filter in dsPIC with DSP Library

I have to make a digital filter with a dsPIC30F, but I don't know much about it. I've read part of the documentation about the dsPIC30F and the DSP Library, and I found a page on Microchip website ...
1
vote
1answer
213 views

DSP Library not working in MPLAB X

I have to make a digital filter with a dsPIC30F4011 (I'm completely new to microcontrollers). I was reading the documentation about the DSP Library to figure out how to use it. I created a simple C ...
1
vote
1answer
68 views

Filtering Audio Signals in MATLAB

I'm trying to apply a filter to an audio signal in MATLAB and having some trouble processing it. So far, I have a transfer function that describes a K-weighted filter, and I am able to create a bode ...
1
vote
1answer
105 views

Decimate ADAR7251 Sigma-Delta ADC Output

I'm working with a Analog Devices ADAR7251 Sigma-Delta ADC. It has multiple sample rates to choose from (1800 kSPS, 1200 kSPS, 900 kSPS, 600 kSPS, 450 kSPS, and 300 kSPS) but my application requires ...
1
vote
0answers
771 views

Low-pass digital filter for 0-10 V, 4-20 mA input

I'm looking for a little direction or recommendations in how to select and implement a low-pass filter in software as my background in signals and systems is quite weak. In particular, I'm interfacing ...
0
votes
3answers
96 views

ADC power supplies monitoring - How to reject short overvoltage pulses

I have an MCU application where the MCU switches on/off and monitors the various power supplies of the board (3.3V, 1.8V, 1.0V etc.). When an under- or over-voltage is detected, an alarm to the system ...
0
votes
2answers
681 views

How to improve my digital filter to extract DC from noises?

Digital filter description: The filter's input are sensor data and output will be provided to a PID controller. Sampling rate: 64kHz Noises spectrum: from DC to 10kHz Filter target: to get DC ...
0
votes
1answer
197 views

filter whose gain increases from minimum to maximum for frequency 400Hz to 1kHz

I want to design high pass filter whose gain should increase from minimum to maximum ( minimum upto 400 Hz maximum for 1 kHz) linearly or exponentially. It must be an active filter and my input signal ...
0
votes
2answers
83 views

Digital vs Analogue Filters From an Non-Audio Perspective

Recently I have been reading about the use of digital filters. By deriving the transfer function of the desired filter (in the s-domain) and multiplying holds (ZOH or FOH). What is the general ...
0
votes
1answer
79 views

What is a Thresh filter?

I was looking at this site and saw the term. While I'm a bit familiar with some DSP terminology, I have never heard of this before. Google did not really help at all. From what the site explores, it ...