# Questions tagged [scipy]

The tag has no usage guidance.

193 questions
Filter by
Sorted by
Tagged with
686 views

### Morphing between two FFTs

I'm a musician and I'm making a script that takes a wave file and snaps each of its frequencies from the fourier transforms to the nearest musical harmonic. Thanks to help from another question I ...
• 79
164 views

### Unexpected peaks in power density following downsampling and filtering

I first applied a 100 Hz lowpass filter to my data, which was recorded at 30000 Hz: ...
1k views

### Should scipy.signal.coherence be 1 for single input and output signals?

I am trying to calculate the coherence between input and output signals. I thought I could work with a single input and a single output time series and calculate the coherence $\gamma^2$ between them. ...
1 vote
405 views

### Help generating coefficients for basic FIR LPF

I'm trying to generate coefficients for a FIR low pass filter to be used in an FPGA. I'm using python (scipy.signal) to attempt to do this, but am having trouble getting coefficients in a usable form....
• 11
515 views

### Outlier Detection after Detrending a Time Series With Missing Values or NaN

Goal Substitute outliers in a time series by most recent valid data Problem The time series (end-of-day stock prices) has several 'uncomfortable' properties: It is non-stationary and can have ...
• 101
2k views

### How to generate random samples of Gaussian distribution directly in the frequency domain?

One can easily draw (pseudo-)random samples from a normal (Gaussian) distribution by using, say, NumPy: ...
201 views

### Can I combine an IIR (an EWMA) with a maximum?

I'd like to have a exponentially weighted moving average (EWMA) which is raised to the value of the input signal whenever this is higher than the filter output. This taking of the maximum shall take ...
• 113
1 vote
14k views

### Avoiding "RuntimeWarning: invalid value encountered in log10" when converting FFT data to dBFS

I've attached some code below that I'm having some issues with. Basically, I need to write a function to get the dBFS value of a signal at a specified Hz value, at a given channel in a .wav file. ...
• 11
24k views

### Why is Scipy implementation of Hilbert() function different from Matlab implementation of the function?

I am trying to fit Hilbert envelop to a high frequency ultrasonic signal of frequency 250 KHZ and sampling rate 12000000. Raw signal looks like below: . I used hilbert() function from scipy.signal ...
• 213
1 vote
1k views

### Trying to implement MATLAB $\tt pwelch$ in Python

I'm implementing an existing MATLAB script in Python and noticing some differences in the behaviour of MATLAB's pwelch function compared to ...
• 121
1k views

### Delay filters in Python using for loop and $\tt lfilter$

I have these two filters as given in recursive form: \begin{align} y_1[i] &= y[i] - y[i-d] + 1.2y_1[i-d] - 0.8y_1[i-2d]\\ y_2[i] &= y[i] - 2y[i-d] + y[i-2d] \end{align} where $d$ is an ...
• 237
5k views

### How to compute the power bands of an eeg signal using python?

so I have an eeg signal (edf format) that has 25 channels and 248832 entries, sampling frequency of 512Hz. I have to compute the frequency bands: – Delta: 0.1-4Hz – Theta: 4-8Hz – Alpha: 8-12Hz – ...
• 113
9k views

### Downsampling and upsampling of a signal in Python

If I want to downsample a signal in Python, is it better to use method resample from SciPy Signal Processing module or method decimate from the same module? What is the difference between these two ...
• 31
1 vote
2k views

### Welch spectrogram

I have been using scipy's spectrogram function (STFT) to compute a PSD spectrogram for a non-stationary signal. I provide X length window (with nperseg = X/10) each ...
• 59
1 vote
358 views

### Understanding why spectral flatness cannot be computed

I have a real signal recorded 512Hz for 1s. After resampling the signal at 256Hz, I would like to compute its spectral flatness. To do so, I start by taking its discrete Fourier transform with ...
• 49
31k views

### Convert RGB Image to Grayscale and Display It (Python + Matplotlib) [closed]

I just started learning image processing and I was trying to read a RGB image then convert it to grayscale. I was hoping for something like this: However, what I get was: I tried using both scipy ...
• 33
428 views

### consecutive filtered blocks with filtfilt

I'm doing basic signal processing in Python. I'm filtering consecutive blocks of a signal with scipy's filtfilt (to get zero phase). I would like to concatenate several blocks after filtering, however,...
• 59
1k views

### Python different autocorrelation with FFT and non-FFT

Im trying to calculate the autocorrelation of soundwaves when I noticed that I get different results with scipys FFT based and with numpys methods. The 4 functions Im using: ...
• 33
956 views

### Forward Backward filter Scipy - $\tt signal.filtfilt$ changes the amplitude when $\tt signal.butter$ is used with $\tt btype='high'$

In the plot below the blue wave is the original signal. The orange wave is after the low pass filter. The green wave is after the high pass filter. I have a noisy ECG signal stored in the ...
1 vote
593 views

### Issue with the time vector returned by $\tt signal.spectrogram$ function

I'm puzzled by some very simple concept with building up a spectrogram. Here is a toy example of the issue: ...
• 59
4k views

### How to implement bandpass filter on complex valued signal?

I am using Scipy to implement bandpass filter but it assumes that positive normalized frequency is passed but I & Q samples range from [Fc-Fs/2,Fc+Fs/2] where Fs is sampling frequency & Fc is ...
1 vote
3k views

### How to design bandpass filter in python when centre frequency is greater than sampling frequency?

I implemented basic bandpass filter using Scipy resource. But how to implement the same when signal is centred at non-zero centre frequency with centre frequency > sampling frequency. I trying to ...
1 vote
9k views

### How to normalize output of $\tt scipy.signal.correlate$

I have 2 different signals and I'm trying to cross-correlate then using Python 2.7 and scipy.signal.correlate. How do I normalize my results (such that the max ...
• 113
2k views

### Do DCT results contain phase spectrum?

I've been working much with numpy.fft lately where just like the documentation says: When the input a is a time-domain signal and ...
• 237
39k views

### Calculating values of frequency bins in Python

I have to use FFT to determine the period of waves inside a signal. After applying FFT on a window of 10000 point from a signal, I get something like this: What I don't understand is that FFT is ...
• 198
7k views

### Python butter filter: choosing between analog and digital filter types

I have a system that performs wireless sampling of data about every 7.5ms (133Hz). Due to it being wireless, I get occasional data drop out. I want to construct a LP butter filter with cut-off ...
• 63
1 vote
586 views

### problem with decimate in scipy 0.18

I use scipy.signal.decimate to downsample a large spectroscopic data-set. This has worked superbly so far. ...
2k views

### Why does python's scipy.signal.dimpulse introduce delay in impulse response?

Consider a simple linear, time invariant system of the form: $y_k = cy_{k-1} + (1-c)x_k$ The impulse response of this system can be computed by either dimpulse or by applying lfilter to a vector ...
• 375
1 vote
386 views

### Need of $\tt abs()$ method when plotting a power spectral density for a given dataset

I am a newbie in signal processing and would like to know the significance of using the abs() function and squaring the values received as an output of ...
1 vote
74 views

### $n\textrm{ Hz}$ waveform sampled at $m\textrm{ Hz}$ per second

Here is an example of plotting a square wave given in SciPy Documentation A $5\textrm{ Hz}$ waveform sampled at $500\textrm{ Hz}$ for 1 second: ...
• 121
222 views

### How to discard coefficients in the frequency domain without losing too much quality?

I was reading a text that shows that one can throw away 66% of the coefficients and gets an image that is still acceptable. I tried to replicate it using python (last example) and selectively ...
1 vote
9k views

### Is there a function in python which returns the Amplitude/Sound Pressure Level of a sound file(like .wav) file?

I found a function called scipy.io.wavefile.read() which returns the sampling rate and an array. But in the documentation, it is not specified that whether the ...
545 views

### Problems designing high pass FIR filter with $f_\textrm{cutoff} \ll f_\textrm{s}$

Is there any inherant problems with high-passing a signal with a very low cutoff frequency compared to the sampling rate? I'm not sure what I am missing as I cant find any info on it. Examples ...
• 101
3k views

### Converting from radians/samples to normalized frequency range $[0.0, 1.0]$?

I'm trying to understand the following code, specifically how to use the results of scipy.signal.freqz where w in ...
• 1,404
311 views

### Scipy.signal.dimpulse(system): how to translate a StateSpace to a "system"? [closed]

The command scipy.signal.dimpulse(system, x0=None, t=None, n=None) does not seem to accept a scipy StateSpace as an input to its ...
1k views

### How does scipy.signal.deconvolve work?

The deconvolve(signal, divisor) function of scipy ...
• 207
4k views

### Butterworth band pass filter

I am trying to build a Butterworth bandpass filter. My intent is to have a pass band between $250\textrm{ Hz}$ and $1000\textrm{ Hz}$. However the plot doesn't look right, as can be seen from the ...
• 133
351 views

### Translating Bessel filter from python to C - odd behavior past the cutoff frequency

I recently translated the code from scipy.signal.bessel to C in order to implement a bessel filter in a piece of analysis ...
• 320
669 views

### discrete digital filtering in python

I am not from DSP background and also not sure if I am posting this in right community. I have basic understanding of resistors, capacitors and filters. My requirement is as follows- The supply ...
1 vote
3k views

### How to design an interpolated notch filter in Python to filter powerline harmonics

I have a a time domain data set that records the magnetic field vs time, which must be processed to reveal an embedded signal. This data also contains power line harmonics (i.e. multiples of 60 Hz) ...
• 111
107 views

### How to know when a sound in a given frequency starts and ends?

I need to detect two sounds (913 Hz and 1370 Hz), knowing the time in which each starts and ends. At this time, I am using a band pass filter (butter), and this is the result: Here is the first time ...
272 views

### Beginner Question: Extracting Features for Image Classification

I'm a Python programmer, but a beginner to image processing :) Apologies if this isn't a suitable question for the forum, happy to rewrite or move. I want to create a supervised classifier to ...
• 121