18
votes
Accepted
Extremely low frequency filters
I guess it depends on several factors, among others the order of the filter, but you have a few possibilities:
Find a signal generator that gets there. These are rather inexpensive nowadays.
Trust ...
- 8,396
13
votes
Performing FFT at low frequencies but high resolution?
I assume for "high speed" you mean a small delay from data collection to the resultant FFT. With a low sample rate, your computational ability isn't the limiting factor, given modern computers. The ...
- 2,888
11
votes
Accepted
Performing FFT at low frequencies but high resolution?
One usually needs to acquire multiple samples per waveform period to get good results from an FFT. The Nyquist limit of 2 samples per period is a lower bound but usually 10 samples per period or more ...
- 11.9k
10
votes
Extremely low frequency filters
I would use my Agilent function generator, which goes down to 1\$\mu\$Hz, a fairly unremarkable (and obsolete) Model 33522A. My Rigol DG4102, I think, similarly has 1\$\mu\$Hz resolution and cost less....
- 384k
10
votes
The term Feed-forward and its meaning?
Feed forward refers to the direction of the signal flow. For feed forward, the direction is, well, forward :-)
I think it is easier to show an example. I know that many "sigma-delta" ADCs (analog to ...
- 80.5k
6
votes
Remove spikes from Load Cell readings
You don't need to 'remove the spikes' so much as 'give the right reading'.
There are at least two good possibilities for what's happening, and they require different software filters. Then there are ...
- 162k
6
votes
Extremely low frequency filters
Option 1: Test on the PC.
If your DSP code is written in C, then you can set up a test harness in GCC or Visual Studio. You know the sample rate for your DSP code, so use Excel to generate a test ...
- 6,030
6
votes
Accepted
Calculate cutoff frequency of a digital IIR filter
With you needing an anti-alias filter for 1/100 of the bandwidth, I'd say that both your single-pole IIR (exponentially weighted moving average) and actual moving averages are out of the question; you'...
- 90.5k
6
votes
Digital signal processing vs. analog signal processing for a 100kHz DAQ project
ADCs usually need an anti-aliasing filter, otherwise frequencies above Fs/2 will alias to frequencies below Fs/2. For example if your sampling frequency is 48kHz and there is no anti-alias filter, a ...
- 72k
5
votes
Accepted
What reduced the noise when multiplying neighbor samples?
You basically squared the signal. If you were sampling properly fast, then the small shift due to multiplying by the next sample instead of the same sample only had minor effect on high frequencies.
...
- 312k
5
votes
FIR Filter 16-Bit
Rescale it. The filter coefficients should be picked so that they all add up to the 16 bit max value. This should make the max value after the multipliers fit in to 32 bits. Then just truncate the 16 ...
- 40.8k
5
votes
Extremely low frequency filters
If you have a D/A converter as well in your DSP system, you could generate this extremely low frequency signal in software an feed it back to your A/D input. Alternatively you could use a D/A Card or ...
- 51
5
votes
Accepted
How can I design a low pass filter using Z transform in Microcontroller?
The usual method to design an IIR filter is to start with a frequency response we want, for example.
$$A(s)= \dfrac{1}{1+\dfrac{s}{\omega_p}}$$
Where \$ \omega_p \$ is the pole frequency in \$ \text{...
- 4,790
5
votes
Accepted
Doubts about IIR filters definition and transfer function
No. In this case, "infinite" really means semi-infinite — nonzero for positive time only. If it were nonzero for any negative time, then it would be non-causal, and therefore not physically ...
- 170k
5
votes
Calculate cutoff frequency of a digital IIR filter
What you propose is often called an "exponentially weighted moving average", and armed with that term, you can probably find a formula (wikipedia discusses this in some way).
Generally, what you ...
- 90.5k
5
votes
RC filter impulse response is exponential decaying but inverse Fourier is Sinc function
Here's the short answer: a first-order lowpass and a rectangular-in-frequency filter don't look the same in the frequency domain. So why should they be the same when you take the inverse Fourier ...
- 45.4k
5
votes
Why using a pi filter when the applied voltage is DC?
C1 and C3 are "standard" power supply decoupling caps. Their purpose is to prevent high frequency noise that might be on the power supply rails from coupling onto the output currents.
C2's ...
- 10.3k
5
votes
Digital signal processing vs. analog signal processing for a 100kHz DAQ project
In two pictures (made using octave) a 1 kHz signal sampled at 1100 sps:
and at 1200 sps:
How could digital processing distinguish those from (respectively) 100 Hz and 200 Hz signals? Aliasing must ...
- 8,487
4
votes
How to improve my digital filter to extract DC from noises?
Your first problem is not insufficient design, but insufficient specification. Please note that 'as much as possible' is not a specification!
Rather than wondering whether any particular filter is ...
- 162k
4
votes
Calculate cutoff frequency of a digital IIR filter
Besides what the others have said, your difference equation leads to this transfer function:
$$H(z)=\frac{\alpha}{1-(1-\alpha)z^{-1}}$$
and evaluating it is done by substituting \$z^{-1}=e^{-j\...
- 21.2k
4
votes
Accepted
Why does this part of an OLED filter light only when orientated correctly?
How does the tinted film only filter in one direction?
That is an OLED screen, not LCD, so the structure is a little different. Instead of having just the top polarizer, an OLED screen has the top ...
- 16k
4
votes
Accepted
DSP low pass filter (IIR) no longer works when changed to a new MCU
Solution:
So, I got it working I am not sure if it was due to poorly documentation of I2S or me not understanding the left/ right aligness of a bit, but after reading this on a forum from one the of ...
- 1,413
4
votes
Accepted
Sigma-delta modulator (ADC), can it be used without sinc3 filter?
Is it possible to work without a sinc3 output filter
Not really in the way you are thinking. You really need to sample every bit coming out and low-pass filter that data stream. The low-pass filter ...
- 45.4k
3
votes
Accepted
Advantages of filtering signals using analog or digital methods?
Two parts to this answer. The first is that there is no such thing as a digital anti-aliasing filter. Before the analog signal can make it into a computational device for processing, one must ...
- 29.6k
3
votes
Advantages of filtering signals using analog or digital methods?
You're forgetting the underlying, rock-bottom requirement for digital filters: The analog input must have a bandwidth less than half the sample rate. Without analog filters on the first ADC, digital ...
- 60.3k
3
votes
LM567 or Custom bandpass filter
Neither options seem very reasonable in 2019.
the RLC is unnecessarily bad a filter, unless you do many stages, which becomes very complicated,
tone detection is very sensitive to more than one tone ...
- 90.5k
Only top scored, non community-wiki answers of a minimum length are eligible