| 1. |
- Akesson, Maria, et al.
(författare)
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Highly Accurate and Noise-Robust Phase Delay Estimation using Multitaper Reassignment
- 2023
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Ingår i: 31st European Signal Processing Conference, EUSIPCO 2023 - Proceedings. - 2219-5491. - 9789464593600 ; , s. 1763-1767
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Konferensbidrag (refereegranskat)abstract
- The recently developed Phase-Scaled Reassignment (PSR) can estimate phase-difference between two oscillating transient signals with high accuracy. However, in low signal-to-noise ratios (SNRs) the performance of commonly applied reassignment techniques is known to deteriorate. In order to reduce variance in low SNR, we propose a multitaper PSR (mtPSR) method for phase-difference estimation between Gaussian transient signals. Three possible variations of this method are investigated and evaluated, mtPSR1, mtPSR2, and mtPSR3. All three variations are shown to outperform state-of-the-art methods and improve estimation accuracy in low SNR. The mtPSR1 is superior in terms of computational efficiency while the mtPSR3 achieves the highest accuracy. The mtPSR technique is also shown to be robust to model assumptions. An example of phase delay estimates of the electrical signals measured from the brain reveals promising results.
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| 2. |
- Brynolfsson, Johan, et al.
(författare)
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A time-frequency-shift invariant parameter estimator for oscillating transient functions using the matched window reassignment
- 2021
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Ingår i: Signal Processing. - : Elsevier BV. - 0165-1684. ; 183
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present the matched window reassignment method, generalizing the results to complex valued signals in multiple dimensions. For an oscillating transient signal with an envelope shape described by an arbitrary twice differentiable function, the reassigned spectrogram, with a matched window, concentrates all energy into one single time-frequency point. An estimator for the parameters of the envelope, in multiple dimensions, is constructed using the above property where the concentration is measured using the Rényi entropy. Furthermore, we present a classification scheme, where an observation is classified based on the concentration when reassigning with a set of model functions. Finally, two examples of parameter estimation from real-world measurements are shown, a one-dimensional time series of a single dolphin click and a two-dimensional time-series of seismic data.
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| 3. |
- Reinhold, Isabella, et al.
(författare)
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A novel Doppler penalty function for the multitaper Wigner-Ville distribution
- 2016
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Ingår i: Proceedings of the 11th IMA International Conference on Mathematics in Signal Processing.
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Konferensbidrag (refereegranskat)abstract
- This paper proposes a novel Doppler penalty kernel used in the computation of multitapers corresponding to the Wigner-Ville distribution. The resulting multitaper spectrogram will approximately fulfil the time-frequency concentration of the Wigner-Ville distribution but also suppress the cross-terms outside a signal dependent Doppler bandwidth, making the penalty kernel appropriate for linear frequency modulated signals. A limited number of tapers are used which results in computationally efficient calculations. A method for selecting a signal dependent Doppler bandwidth which balances the trade-off between auto-term resolution and cross-term suppression is also proposed. The time-frequency concentration of the proposed method is compared to other penalty kernel methods and a lag-independent kernel with compact support. The performance for white noise disturbances is also evaluated. Estimation of heart rate variability data exemplify the use of the penalty kernel.
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| 4. |
- Reinhold, Isabella, et al.
(författare)
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Efficient Thomson Spectral Estimator with Time-shifted Windows
- 2019
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Ingår i: 2019 IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP 2019 - Proceedings. - 9781479981311 ; 2019-May, s. 4983-4987
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Konferensbidrag (refereegranskat)abstract
- In this paper optimal spectral analysis window shapes, using weighted discrete prolate spheroidal sequences as basis functions, are proposed. These windows are not typically positive or even. The windows are time-shifted, combining the computational efficiency of the Welch method and the appealing property of predefined frequency resolution of the Thomson spectral estimator. The parameters of the optimal windows are found by minimising the resulting spectral covariances and optimising the window overlap, for the predetermined frequency resolution and number of windows. The windows are found to have low side lobes, giving small spectral leakage, and the final spectral estimate gives close to optimal variance reduction, i.e. the covariance between different sub-spectra is very small.
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| 5. |
- Reinhold, Isabella
(författare)
-
High resolution time-frequency representations
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Non-stationary signals are very common in nature, e.g. sound waves such as human speech, bird song and music. It is usually meaningful to describe a signal in terms of time and frequency. Methods for doing so exist and are well defined. From the time representation it is possible to see the oscillations or waves of the signal and if the signal changes over time. From the frequency representation, obtained from the Fourier transform, the frequency decomposition of the signal can be seen, i.e. which frequencies the signal contains.However the time and frequency representations are not unique for any given signal, i.e. the transformation from time to frequency is not injective. It is therefore, especially for non-stationary and multi-component signals, important to study a joint time-frequency (TF) representation, which shows how the frequency content of the signal varies with time. This is done in the field of time-frequency analysis, which is the topic of this thesis.There exist many different joint TF representations for any given signal and choosing an appropriate representation is most often not straight forward. Unfortunately there exist no optimal TF representation for all signals and finding good representations, especially for multi-component signals is a complex problem.In this thesis, methods for obtaining good TF representations, for two types of non-stationary and multi-component signals, and for extracting meaningful information from these representations, are developed. The two types of signals are long, frequency modulated signals and short, transient signals. Even though the types of signals are very different and require very different TF representations, the aim is to resolve components that are close in time, frequency or both. This requires TF representations with high resolution.For the long, frequency modulated signals, a signal adaptive method, which enables automatic comparison between different TF representations, is proposed. For the short, transient signals, a method which finds the TF centres of transient pulses and counts the number of pulses in a signal is presented. An approach for determining the (time) shape of transient pulses is also given.
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| 6. |
- Reinhold, Isabella, et al.
(författare)
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Non-parametric Envelope Estimation for the Matched Window Reassignment
- 2021
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Ingår i: 29th European Signal Processing Conference, EUSIPCO 2021 - Proceedings. - 2219-5491. - 9789082797060 ; 2021-August, s. 1920-1924
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Konferensbidrag (refereegranskat)abstract
- The reassigned spectrogram is a powerful tool for analysing non-stationary signals, and in an ideal setting it gives perfect time and frequency localisation. A method very well suited for oscillating transient signals is the matched window reassignment, which requires a matching window, i.e. the envelope of the transient, to be known or estimated beforehand. This paper proposes a novel method for estimating the envelope of noisy transients, using a non-parametric and computationally efficient approach. The estimated envelopes are used to calculate the matched window reassignment, obtaining estimates of the time-frequency centre of the transients. The reassignment using the estimated envelopes is shown to give good estimates of the time-frequency centres, and good localisation in time and frequency. The novel envelope estimation approach is illustrated on measured marine biosonar data.
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| 7. |
- Reinhold, Isabella, et al.
(författare)
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Objective detection and time-frequency localization of components within transient signals
- 2018
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966. ; 143:4, s. 2368-2378
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Tidskriftsartikel (refereegranskat)abstract
- An automatic component detection method for overlapping transient pulses in multi-component signals is presented and evaluated. The recently proposed scaled reassignment technique is shown to have the best achievable resolution for closely located Gaussian shaped transient pulses, even in heavy disruptive noise. As a result, the method automatically detects and counts the number of transients, giving the center times and center frequencies of all components with considerable accuracy. The presented method shows great potential for applications in several acoustic research fields, where coinciding Gaussian shaped transients are analyzed. The performance is tested on measured data from a laboratory pulse-echo setup and from a dolphin echolocation signal measured simultaneously at two different locations in the echolocation beam. Since the method requires little user input, it should be easily employed in a variety of research projects.
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| 8. |
- Reinhold, Isabella, et al.
(författare)
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Optimal time–frequency distributions using a novel signal adaptive method for automatic component detection
- 2017
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Ingår i: Signal Processing. - : Elsevier BV. - 0165-1684. ; 133, s. 250-259
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Tidskriftsartikel (refereegranskat)abstract
- Finding objective methods for assessing the performance of time–frequency distributions (TFD) of measured multi-component signals is not trivial. An optimal TFD should have well resolved signal components (auto-terms) and well suppressed cross-terms. This paper presents a novel signal adaptive method, which is shown to have better performance than the existing method, of automatically detecting the signal components for TFD time instants of two-component signals. The method can be used together with a performance measure to receive automatic and objective performance measures for different TFDs, which allows for an optimal TFD to be obtained. The new method is especially useful for signals including auto-terms of unequal amplitudes and non-linear frequency modulation. The method is evaluated and compared to the existing method, for finding the optimal parameters of the modified B-distribution. The performance is also shown for an example set of Heart Rate Variability (HRV) signals.
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| 9. |
- Reinhold, Isabella, et al.
(författare)
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Quality of Academic Writing for Engineering Students at Lund University
- 2017
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Ingår i: Transforming patterns through the scholarship of teaching and learning : the 2nd European conference for the scholarship of teaching and learning | Lund, Sweden, June 8-9 2017 - the 2nd European conference for the scholarship of teaching and learning | Lund, Sweden, June 8-9 2017.
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Konferensbidrag (refereegranskat)abstract
- The development of good writing skills is fundamental not only to publish scientific results, but also to have a deeper understanding of complex subjects. However reports from the Swedish Higher Education Authority from 2012-2015 suggest that engineering students at Lund University have unsatisfactory academic writing skills. Our paper investigates how students of the Faculty of Engineering at Lund University perceive academic writing and the effects of a writing intervention.To obtain information on students’ education in, attitude, perception of its difficulty and their own skill towards academic writing, we constructed a survey which was sent out to engineering students at Lund University. This yielded 62 responses showing that students want more opportunities to develop their writing, but that they grade their writing skill high and the difficulty low.The effects of a simple writing intervention, briefly discussing the importance of good writing practices during a laboratory session, was investigated for one student group. This was done using a random selection of laboratory reports for one control group and one intervention group. The overall quality of the students’ writing was not significantly improved with the intervention. However the quality of the conclusions, the report section with the lowest quality rating, was higher for the intervention group.
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| 10. |
- Reinhold, Isabella
(författare)
-
Spectral Analysis for Signal Detection and Classification : Reducing Variance and Extracting Features
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Spectral analysis encompasses several powerful signal processing methods. The papers in this thesis present methods for finding good spectral representations, and methods both for stationary and non-stationary signals are considered. Stationary methods can be used for real-time evaluation, analysing shorter segments of an incoming signal, while non-stationary methods can be used to analyse the instantaneous frequencies of fully recorded signals. All the presented methods aim to produce spectral representations that have high resolution and are easy to interpret. Such representations allow for detection of individual signal components in multi-component signals, as well as separation of close signal components. This makes feature extraction in the spectral representation possible, relevant features include the frequency or instantaneous frequency of components, the number of components in the signal, and the time duration of the components. Two methods that extract some of these features automatically for two types of signals are presented in this thesis. One adapted to signals with two longer duration frequency modulated components that detects the instantaneous frequencies and cross-terms in the Wigner-Ville distribution, the other for signals with an unknown number of short duration oscillations that detects the instantaneous frequencies in a reassigned spectrogram. This thesis also presents two multitaper methods that reduce the influence of noise on the spectral representations. One is designed for stationary signals and the other for non-stationary signals with multiple short duration oscillations. Applications for the methods presented in this thesis include several within medicine, e.g. diagnosis from analysis of heart rate variability, improved ultrasound resolution, and interpretation of brain activity from the electroencephalogram.
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| 11. |
- Reinhold, Isabella, et al.
(författare)
-
The multitaper reassigned spectrogram for oscillating transients with Gaussian envelopes
- 2022
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Ingår i: Signal Processing. - : Elsevier BV. - 0165-1684. ; 198
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Tidskriftsartikel (refereegranskat)abstract
- Joint time-frequency representations are important tools when estimating the instantaneous frequency. The widely used spectrogram is known to have poor energy localisation, which the reassignment method improves. However, the reassignment method is sensitive to noise. In this paper we present a multitaper reassigned spectrogram (MTRS) that is robust to noise and tailored to short duration transient signals. The MTRS is designed for oscillating transients with Gaussian envelopes and uses the Hermite functions as windows. The novel reassignment coordinates needed for the MTRS are derived in this paper. The MTRS localises energy at the instantaneous frequencies of transients, while white Gaussian noise is made flatter by the use of multiple windows. It is shown that the MTRS is more noise robust compared to reassignment with just one window, and that it improves on the energy localisation of the spectrogram. Thus, our MTRS is sparse, easy to interpret, and well suited for instantaneous frequency estimation, even for signals with overlapping transients and low signal-to-noise ratios.
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| 12. |
- Reinhold, Isabella, et al.
(författare)
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The scaled reassigned spectrogram adapted for detection and localisation of transient signals
- 2017
-
Ingår i: European Signal Processing Conference. - 9780992862671 ; , s. 937-941
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Konferensbidrag (refereegranskat)abstract
- The reassigned spectrogram can be used to improve the readability of a time-frequency representation of a non-stationary and multi-component signal. However for transient signals the reassignment needs to be adapted in order to achieve good localisation of the signal components. One approach is to scale the reassignment. This paper shows that by adapting the shape of the time window used with the spectrogram and by scaling the reassignment, perfect localisation can be achieved for a transient signal component. It is also shown that without matching the shape of the window, perfect localisation is not achieved. This is used to both identify the time-frequency centres of components in a multi-component signal, and to detect the shapes of the signal components. The scaled reassigned spectrogram with the matching shape window is shown to be able to resolve close components and works well for multi-components signals with noise. An echolocation signal from a beluga whale (Delphinapterus leucas) provides an example of how the method performs on a measured signal.
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| 13. |
- Sandsten, Maria, et al.
(författare)
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A multitaper reassigned spectrogram for increased time-frequency localization precision
- 2020
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Ingår i: ICASSP 2020 - 2020 IEEE International Conference on Acoustics, Speech and Signal Processing. - 9781509066315 ; , s. 5310-5314
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Konferensbidrag (refereegranskat)abstract
- The reassignment vectors of the matched reassigned spectrogram (MRS) have shown to be sensitive to noise, with resulting degraded precision in the time-frequency localization. In this paper we propose a multitaper reassignment (mtRS) method for estimation of time- and frequency locations of Gaussian envelope transients. We present novel expressions for the reassignment vectors with use of a non-matched window. These reassignment vectors are then averaged with the usual MRS reassignment vectors forming a multitaper reassignment with use of orthogonal windows. The mtRS is shown to give a higher precision in the time- and frequency estimates in low SNR compared to the usual MRS and also in comparison to other state-of-the-art methods.
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| 14. |
- Sandsten, Maria, et al.
(författare)
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A Novel Multitaper Reassignment Method for Estimation of Phase Synchrony
- 2021
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Ingår i: 29th European Signal Processing Conference, EUSIPCO 2021 - Proceedings. - 2219-5491. - 9789082797060 ; 2021-August, s. 2164-2168
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Konferensbidrag (refereegranskat)abstract
- The matched phase reassignment, developed to estimate phase synchrony of transient oscillatory signals, is extended into a multitaper phase reassignment (MTPR) method. The method gives perfect time-frequency localization for two transients with zero phase difference and estimates of time locations and oscillatory frequencies in low signal-to-noise ratios. For different signal-to-noise ratios between channels a suggestion of corrected reassignment vector expressions is given, resulting in minimized variance. The MTPR outperforms the matched phase reassignment as well as state-of-the-art methods, such as Pearson's linear correlation, time-frequency cross-spectrogram phase estimation and the Phase Lag Index method. An example of estimated phase differences, time locations and oscillatory frequencies of electrical signals measured from the brain is also shown.
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| 15. |
- Sandsten, Maria, et al.
(författare)
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Automatic time-frequency analysis of echolocation signals using the matched Gaussian multitaper spectrogram
- 2017
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Ingår i: INTERSPEECH 2017. ; , s. 3048-3052
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Konferensbidrag (refereegranskat)abstract
- High-resolution time-frequency (TF) images of multi-component signals are of great interest for visualization, feature extraction and estimation. The matched Gaussian multitaper spectrogram has been proposed to optimally resolve multi-component transient functions of Gaussian shape. Hermite functions are used as multitapers and the weights of the different spectrogram functions are optimized. For a fixed number of multitapers, the optimization gives the approximate Wigner distribution of the Gaussian shaped function. Increasing the number of multitapers gives a better approximation, i.e. a better resolution, but the cross-terms also become more prominent for close TF components. In this submission, we evaluate a number of different concentration measures to automatically estimate the number of multitapers resulting in the optimal spectrogram for TF images of dolphin echolocation signals. The measures are evaluated for different multi-component signals and noise levels and a suggestion of an automatic procedure for optimal TF analysis is given. The results are compared to other well known TF estimation algorithms and examples of real data measurements of echolocation signals from a beluga whale (Delphinapterus leucas) are presented.
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| 16. |
- Sandsten, Maria, et al.
(författare)
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Parameter Estimation from the Cross-Spectrogram Reassignment Vectors
- 2021
-
Ingår i: 29th European Signal Processing Conference, EUSIPCO 2021 - Proceedings. - 2219-5491. - 9789082797060 ; 2021-August, s. 1915-1919
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Konferensbidrag (refereegranskat)abstract
- In this paper we propose a novel technique to estimate the parameters of two Gaussian envelope oscillatory signals, with the same time-locations and oscillatory frequencies but possibly different phases. The phase difference and the length of the Gaussian envelope are estimated directly from the slopes of the corresponding cross-spectrogram reassignment vectors. Including the phase difference and the envelope length in the scaled reassignment of the cross-spectrogram will give a perfectly concentrated time-frequency spectrum where the location of the maximum gives estimates of the time and oscillatory frequency parameters. The proposed method is evaluated for different SNRs and is also compared to state-of-the-art techniques for phase estimation of oscillatory electrical activity measured from the brain.
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| 17. |
- Sandsten, Maria, et al.
(författare)
-
The matched reassigned cross-spectrogram for phase estimation
- 2020
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Ingår i: ICASSP 2020 - 2020 IEEE International Conference on Acoustics, Speech and Signal Processing. - 9781509066315 ; , s. 5960-5964
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Konferensbidrag (refereegranskat)abstract
- In this paper, the matched reassigned spectrogram is expanded into a novel matched phase reassignment (MPR) method based on the reassigned cross-spectrogram. It is shown that for two phase synchronized oscillating transient signals, the method gives perfect time-frequency (TF) localization. The MPR is thereby a TF local measure of phase synchronization and can also be used to measure phase difference between short transient signals. We explore the technique to measure the phase difference, and compare to commonly used phase estimators, for different types of disturbances. We also investigate the methods ability to classify phase synchronized and non-synchronized signals. Simulations show that the MPR method outperforms the state-of-the-art methods. An illustrative example of phase difference estimates of the electrical signals measured from the brain is included.
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| 18. |
- Sandsten, Maria, et al.
(författare)
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The matched reassignment applied to echolocation data
- 2019
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Ingår i: ICASSP 2019 - 2019 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). - 1520-6149 .- 2379-190X. - 9781479981311 - 9781479981328 ; , s. 8236-8240
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Konferensbidrag (refereegranskat)abstract
- Previous studies have shown that measurements of beluga whale (Delphinapterus leucas) and bottlenose dolphin (Tur-siops truncatus) echolocation signals at off-axis angles may be well modeled using a Gaussian bell function or a chirped Gaussian function as envelope. In this paper, we apply a novel technique, the matched window reassignment, for investigation of a range of models of dolphin echolocation transients. Using a set of parameterized skewed envelopes and a dictionary-based estimation algorithm, it is shown that the Rényi entropy can be used as an evaluation measure of the model fit. Acoustic recordings from an array of hydrophones of a beluga's echolocation signal are investigated, where the Gaussian envelope frequency modulation function resulted in the lowest Rényi entropy mean and the two-parametric Gum-bel model showed the best observed fit.
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| 19. |
- Sandsten, Maria, et al.
(författare)
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The Matched Window Reassignment
- 2018
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Ingår i: 26th European Signal Processing Conference, EUSIPCO 2018. - 9789082797015 ; , s. 2340-2344
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Konferensbidrag (refereegranskat)abstract
- In this paper we calculate reassigned spectrogramsusing the envelope of an arbitrary signal as matched window. Weshow that the matched window then give the perfectly localizedreassignment for any time-translated and frequency-modulatedtransient signal with corresponding envelope. The general expressions of the corresponding scaled reassignment vectors arederived and the matched window reassignment is evaluatedfor time-frequency localization as well as for classification. Theresults show that the accuracy in time- and frequency locationis high also when the signal envelope deviates from the matchedwindow and when the SNR is reasonable large. The classificationperformance based on the matched window reassignment and theRényi entropy is robust to signal envelope deviations as well asto disturbing noise.
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| 20. |
- Starkhammar, Josefin, et al.
(författare)
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Detailed analysis of two detected overlaying transient components within the echolocation beam of a bottlenose dolphin (Tursiops truncatus)
- 2019
-
Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966. ; 145:4, s. 2138-2148
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Tidskriftsartikel (refereegranskat)abstract
- Dolphin echolocation clicks measured far off-axis contain two time-separated components. Whether these components overlap and appear as a single signal on axis has received little attention. Here, the scaled reassigned spectrogram analysis was used to examine if bottlenose dolphin (Tursiops truncatus) clicks measured near- or on-axis of the echolocation beam contained overlapping components. Across click trains, the number of overlapping components spatially varied within the echolocation beam. Two overlapping components were found to predominantly occur in the upper portion of the beam, whereas the lower portion of the beam predominantly contained a single component. When components overlapped, the trailing component generally had a higher center frequency and arrived less than 5 μs after the leading component. The spatial relationship of components was consistent with previous findings of two vertically distinct beam lobes with separated frequency content. The two components in the upper portion of the beam possibly result from a single transient click propagating through a geometrically dispersive media; specifically, the slower sound speed of the dolphin melon's core slightly delays the more directional, high frequency energy of the click, whereas the less directional, lower frequency energy propagates through more peripheral but higher sound speed portions of the melon.
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| 21. |
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| 22. |
- Starkhammar, Josefin, et al.
(författare)
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Scaled reassigned spectrograms applied to linear transducer signals
- 2021
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Ingår i: JASA Express Letters. - : Acoustical Society of America (ASA). - 2691-1191. ; 1:5
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Tidskriftsartikel (refereegranskat)abstract
- This study evaluates the applicability of scaled reassigned spectrograms (ReSTS) on ultrasound radio frequency data obtained with a clinical linear array ultrasound transducer. The ReSTS's ability to resolve axially closely spaced objects in a phantom is compared to the classical cross-correlation method with respect to the ability to resolve closely spaced objects as individual reflectors using ultrasound pulses with different lengths. The results show that the axial resolution achieved with the ReSTS was superior to the cross-correlation method when the reflected pulses from two objects overlap. A novel B-mode imaging method, facilitating higher image resolution for distinct reflectors, is proposed.
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