New Trends in Biologically-Inspired Audio Coding

This book chapter deals with the generation of auditory-inspired spectro-temporal features aimed at audio coding. To do so, we first generate sparse audio representations we call spikegrams, using projections on gammatone or gammachirp kernels that generate neural spikes. Unlike Fourier-based representations, these representations are powerful at identifying auditory events, such as onsets, offsets, transients and harmonic structures. We show that the introduction of adaptiveness in the selection of gammachirp kernels enhances the compression rate compared to the case where the kernels are non-adaptive. We also integrate a masking model that helps reduce bitrate without loss of perceptible audio quality. We then quantize coding values using the genetic algorithm that is more optimal than uniform quantization for this framework. We finally propose a method to extract frequent auditory objects (patterns) in the aforementioned sparse representations. The extracted frequency-domain patterns (auditory objects) help us address spikes (auditory events) collectively rather than individually. When audio compression is needed, the different patterns are stored in a small codebook that can be used to efficiently encode audio materials in a lossless way. The approach is applied to different audio signals and results are discussed and compared. This work is a first step towards the design of a high-quality auditory-inspired \"object-based\" audio coder

Mass fabrication of high-resolution hydrogels by a high-speed process using a thermal 3D screen printing method.

Hydrogel is a class of material described as ‘solid water’: it maintains properties of liquid water while being physically constrained like a solid. The hydrophilic polymer networks of hydrogels have the strength to absorb and retain a significant amount of water, as much as 99% by weight. This makes it suitable for a diverse range of applications such as tissue engineering, chromatography purification and viral vector separation. Natural hydrogels, made of natural polymers such as starch, alginate, and cellulose, demonstrate common characteristics including permeability, nontoxicity, biocompatibility, and biodegradability. Cellulose is the most abundant organic compound on Earth with fascinating structures and properties. Hydrogel developed from cellulose is of particular interest due to its characteristics of hydrophilicity, solute permeability, and nontoxicity. Aqueous solutions of NaOH/urea are a common solvent for cellulose. Heating or cooling the solution causes an irreversible gel to form. When a non-solvent such as water or acetone is introduced to the gel, the cellulose precipitates, and if water is present, forms a stable hydrogel. An advanced fabrication technique is necessary in order to create the desired geometry, such as a highly complex Schoen Gyroid, made of cellulose hydrogel. The fabricated cellulose hydrogel can be used in various applications including chromatography purification and viral vector separation. Additive manufacturing has the capability to fabricate complex geometries of cellulose hydrogel. It has rapidly emerged as a disruptive technology to build parts, enabling increased design complexity and an ever-increasing range of materials. However, the size and print resolution required for a complex cellulose hydrogel model have a dramatic impact on printing speed. As a result, large batch manufacturing of cellulose hydrogels using additive manufacturing has not been achieved to date. Current methods are also limited by their inability to manufacture complicated shapes. This is due to a lack of suitable support material, which plays an important role in holding up overhanging regions during the printing process. This thesis aims to overcome the current limitations of 3D printing hydrogels, proposing solutions that increase the speed of the process, enable the fabrication of large and complex parts, and ultimately make batch manufacturing hydrogels more economical without sacrificing high resolution. This project has succeeded in developing a method of batch manufacturing large, high resolution cellulose hydrogel parts at a high-speed fabrication rate. A machine, referred to as a thermal 3D screen printer, was prototyped and successfully tested. For the 3D screen printing process, a three-dimensional CAD model is sliced into individual layers of a predefined thickness. A stencil made of thin metal shim is produced for each layer. Successive stencils are used to print wax, which forms a mould in which cellulose hydrogel is cast. After casting, the wax mould is removed in hot water and recycled for further use and the cellulose hydrogel object is fabricated. Thermal 3D screen printed wax moulds can be used to print an extremely large range of material, such as polymers, metals and ceramics; however, the focus of this research was on printing cellulose solutions for the manufacture of structured cellulose hydrogels. The material selection process for the mould material showed that sacrificial wax is suitable for casting complex geometries. The properties investigated are rheological and thermophysical properties, wettability, surface roughness, material interaction, and the effects of different mould removal methods. The thermal 3D screen printed wax mould was optimised using the Taguchi statistical method. Process parameter optimisation showed that the selected printing parameters have a significant effect on 3D screen print quality: listed in declining order of significance, these parameters are squeegee speed, squeegee pressure and printing temperature. The main objective of this project was to explore a manufacturing method for mass fabricating monolithic cellulose hydrogel columns with a TPMS geometry. As a result, a thermal 3D screen printing method with an ultra-fast fabrication process capable of mass fabricating wax moulds was proposed, designed, prototyped, tested, and developed to successfully fabricate cellulose hydrogel

Perceptual Coding of Narrow-band Audio Signals

Abstract—This paper describes a coding paradigm using coding tools based on the characteristics of the human hearing system so as to accommodate a wide range of narrow-band audio inputs without annoying artifacts at low rates (down to 8 kb/s). The narrow-band perceptual audio coder (NPAC) employs a variety of algorithms to account for the perceptually irrelevant parts of the input signal in addition to statistical redundancies. The new algorithms used in the NPAC coder include a perceptual error measure in training the codebooks and selecting the best codewords which takes into account the audible parts of the quantization noise, a perception-based bit-allocation algorithm and a new predictive scheme to vector quantize the scale factors. The NPAC coder delivers acceptable quality without annoying artifacts for most narrow-band audio signals at around 1 bit/sample. Informal subjective tests have shown that the NPAC coder outperforms a commercial low-rate music coder operating at 8 kb/s. Index Terms—Adaptive bit allocation, masking model, modified discrete cosine transform filter bank, narrow-band audio coding, perceptual audio coding, perceptual distortion, perceptual vector quantization, predictive vector quantization

A Novel Additive Manufacturing Method of Cellulose Gel

Screen-additive manufacturing (SAM) is a potential method for producing small intricate parts without waste generation, offering minimal production cost. A wide range of materials, including gels, can be shaped using this method. A gel material is composed of a three-dimensional cross-linked polymer or colloidal network immersed in a fluid, known as hydrogel when its main constituent fluid is water. Hydrogels are capable of absorbing and retaining large amounts of water. Cellulose gel is among the materials that can form hydrogels and, as shown in this work, has the required properties to be directly SAM, including shear thinning and formation of post-shearing gel structure. In this study, we present the developed method of SAM for the fabrication of complex-shaped cellulose gel and examine whether successive printing layers can be completed without delamination. In addition, we evaluated cellulose SAM without the need for support material. Design of Experiments (DoE) was applied to optimize the SAM settings for printing the novel cellulose-based gel structure. The optimum print settings were then used to print a periodic structure with micro features and without the need for support material

3D Printing of Gelled and Cross-Linked Cellulose Solutions; an Exploration of Printing Parameters and Gel Behaviour

In recent years, 3D printing has enabled the fabrication of complex designs, with low-cost customization and an ever-increasing range of materials. Yet, these abilities have also created an enormous challenge in optimizing a large number of process parameters, especially in the 3D printing of swellable, non-toxic, biocompatible and biodegradable materials, so-called bio-ink materials. In this work, a cellulose gel, made out of aqueous solutions of cellulose, sodium hydroxide and urea, was used to demonstrate the formation of a shear thinning bio-ink material necessary for an extrusion-based 3D printing. After analysing the shear thinning behaviour of the cellulose gel by rheometry a Design of Experiments (DoE) was applied to optimize the 3D bioprinter settings for printing the cellulose gel. The optimum print settings were then used to print a human ear shape, without a need for support material. The results clearly indicate that the found settings allow the printing of more complex parts with high-fidelity. This confirms the capability of the applied method to 3D print a newly developed bio-ink material