Digital Signal Processing Foundations

Signals are all around us and come in a wide variety of shapes and forms. When we speak we create pressure variations in the air which generate audio signals; earthquakes produce large seismic signals; healthcare professionals monitor ECG signals which capture the electrical activity of the heart; radio, internet and telephone signals are being transmitted across the world; the list of signals is endless! (see 2 minute video at pzdsp.com/vid1 for some examples) Digital signal processing (DSP) is primarily about making use of computers to help us analyse and manipulate signals in order to help us with our everyday lives. To get a flavour of where DSP is being used check out the lists below; it really is a key component in many innovative solutions and products in recent time

Audio Time-Scale Modification

Audio time-scale modification is an audio effect that alters the duration of an audio signal without affecting its perceived local pitch and timbral characteristics. There are two broad categories of time-scale modifications algorithms, time-domain and frequency-domain. The computationally efficient time-domain techniques produce high quality results for single pitched signals such as speech, but do not cope well with more complex signals such as polyphonic music. The less efficient frequency-domain techniques have proven to be more robust and produce high quality results for a variety of signals; however they introduce a reverberant artefact into the output. This dissertation focuses on incorporating aspects of time-domain techniques into frequency-domain techniques in an attempt to reduce the presence of the reverberant artefact and improve upon computational demands. From a review of prior work it was found that there are a number of time-domain algorithms available and that the choice of algorithm parameters varies considerably in the literature. This finding prompted an investigation into the effects of the choice of parameters and a comparison of the various techniques employed in terms of computational requirements and output quality. The investigation resulted in the derivation of an efficient and flexible parameter set for use within time-domain implementations. Of the available frequency-domain approaches the phase vocoder and time-domain/subband techniques offer an efficiency and robustness advantage over sinusoidal modelling and iterative phase update techniques, and as such were identified as suitable candidates for the provision of a framework for further investigations. Following from this observation, improvements in the quality produced by time-domain/subband techniques are realised through the use of a bark based subband partitioning approach and effective subband synchronisation techniques. In addition, computational and output quality improvements with a phase vocoder implementation are achieved by taking advantage of a certain level of flexibility in the choice of phase within such an implementation. The phase flexibility established is used to push or pull phase values into a phase coherent stage. Further improvements are realised by incorporating features of time-domain algorithms into the system in order to provide a ‘good’ initial set of phase estimates; the transition to ‘perfect’ phase coherence is significantly reduced through this scheme, thereby improving the overall output quality produced. The result is a robust and efficient time-scale modification algorithm which draws upon various aspects of a number of general approaches to time-scale modification

Online Quizzes

Quiz within a virtual learning environment. Generally the quizzes are based on numerical responses, however some multiple choice questions. The quizzes are geared towards the level of the student and the information being reinforced

The Discrete Fourier Transform - A practical approach

These notes on the Discrete Fourier Transform include numerous practical examples that make use of audio signals

BASICS: Building a System to Ingrain Core Competencies within Students

The aim of the project is to develop a system which will promote a solid knowledge of programmes’ “core competencies” amongst students. This will be achieved by building a set of online quizzes which students will undertake on a regular basis throughout the delivery of programme modules. Quizzes will include feedback with links to web-based activities/information to help students develop their understanding

Time Scale Modification of Music using a Subband Approach Based on the Bark Scale

Time-domain time-scaling algorithms are efficient in comparison to their frequency-domain counterparts, but they rely upon the existence of a quasi-periodic signal to produce a high quality output. This requirement makes them unsuitable for use on multi-pitched signals such as polyphonic music. However, time-domain techniques applied on a subband basis can resolve the multi-pitch problem. The authors propose an improved subband implementation based upon the bark scale for the time scale modification of music. The new subband approach is supported by psychoacoustic and music theory and subjectively through informal listening tests

An Efficient Phasiness Reduction Technique for Moderate Audio Time-scale Modification

Phase vocoder approaches to timescale modification of audio introduce a reverberant/phasy artifact into the time-scaled output due to a loss in phase coherence between short-time Fourier transform (STFT) bins. Recent improvements to the phase vocoder have reduced the presence of this artifact, however, it remains a problem. A method of time-scaling is presented that results in a further reduction in phasiness, for moderate timescale factors, by taking advantage of some flexibility that exists in the choice of phase required so as to maintain horizontal phase coherence between related STFT bins. Furthermore, the approach leads to a reduction in computational load within the range of time-scaling factors for which phasi-ness is reduced

Multi-Channel Audio Time-Scale Modification

Phase vecoder based approaches to audio time-scale modification introduce a reverberant artefact into the time scaled output. Recent techniques have been developed to reduce the presence of this artefact; however, these techniques have the effect of introducing additional issues relating to their application to multi-channel recordings. This paper addresses these issues by collectively analysing all channels prior to time-scaling each individual channel

The phantom menace: spatial abilities and STEM outreach to fight underrepresentation in STEM

Spatial abilities are an important, and often overlooked, component of Science, Technology, Engineering and Mathematics (STEM) education with skills like spatial visualisation and mental rotation being important for technical professions such as engineering. Individual differences in spatial abilities have been reported throughout the years. Factors such as being female or having a low-socioeconomic status are linked with lower spatial abilities level. Spatial abilities training interventions have proven to be effective, with some showing improvements, not only in spatial abilities level, but also in the success and retention of students enrolled on STEM degree programmes, especially for women. In todays’ technological society, STEM outreach activities are a common method to promote STEM for children, showing them role models in the area, and improving their self-efficacy, sense of belonging and motivation to follow careers in STEM. At the same time, the underrepresentation seen in the area (e.g., women; LGBTQ+ community; ethnic minorities; and other marginalised groups) needs to be addressed in order to enhance the inclusive environment of these fields. This concept paper discusses review work in relation to underrepresented groups and how future spatial abilities studies should consider integrating the knowledge from past spatial abilities studies into STEM outreach activities. This integration can make spatial training available to more people, revealing itself to be a useful tool in helping diminish underrepresentation in STEM

A comparison of time-domain time-scale modification algorithms

Time-domain approaches to time-scale modification are popular due to their ability to produce high quality results at a relatively low computational cost. Within the category of time-domain implementations quite a number of alternatives exist, each with their own computational requirements and associated output quality. This paper provides a computational and objective output quality assessment of a number of popular time-domain time-scaling implementations; thus providing a means for developers to identify a suitable algorithm for their application of interest. In addition, the issues that should be considered in developing time-domain algorithms are outlined, purely in the context of a waveform editing procedure