Audio application based on FreeRTOS operating system

This current report describes in detail how the Quartet code for a Microchip PIC18 microcontroller, developed by Pere Domenech in his Final Degree Project, has been migrated to a Microchip PIC24 microcontroller. The original Real Time Operating System has also been migrated from OSA RTOS to FreeRTOS. The RTOS modification will allow future upgrades without the need to change the RTOS. The Quartet software is an audio synthesizer which uses a low-pass filtered PWM output to create a mono audio signal. The original code has 3 different instruments and 4 voices: Bass, Violin, Guitar 1 and Guitar 2. Each instrument has its own sound, specific waveform and envelope. Each voice has its own score. The 4 voices are mixed during the synthesis and played through a single PWM microcontroller output. This report explains step by step the software migration process: Operating System migration, Compiler migration and Microcontroller Instructions migration. The process is explained in detail. Therefore, it is highly recommended to read it while studying the final PIC24 Quartet code. At the end of the report, the hardware validation and experimental modifications are explained. Finally, some future improvements, limitations and suggestions are commented. This project is a continuation of the Quartet code for microcontrollers but it is clear that more improvements and modifications will be done in the future

Preliminary candidate advanced avionics system for general aviation

An integrated avionics system design was carried out to the level which indicates subsystem function, and the methods of overall system integration. Sufficient detail was included to allow identification of possible system component technologies, and to perform reliability, modularity, maintainability, cost, and risk analysis upon the system design. Retrofit to older aircraft, availability of this system to the single engine two place aircraft, was considered

An automated stall-speed warning system

The development and testing of a stall-speed warning system for the OV-1C was examined. NASA designed and built an automated stall-speed warning system which presents both airspeed and stall speed to the pilot. The airspeed and stall speed are computed in real time by monitoring the basic aerodynamic parameters (dynamic pressure, horizontal and vertical accelerations, and pressure altitude) and other parameters (elevator and flap positions, engine torques, and fuel flow). In addition, an aural warning at predetermined stall margins is presented to the pilot through a voice synthesizer. Once the system was designed and installed in the aircraft, a flight-test program of less than 20 hrs was anticipated to determine the stall-speed software coefficients. These coefficients would then be inserted in the system's software and then test flown over a period of about 10 hr for the purpose of evaluation

A novel continuous pitch electronic wind instrument controller

We present a design for an electronic continuous pitch wind controller for musical performance. It uses a combination of linear position, magnetic reed, and air pressure sensors to generate three fully continuous control dimensions. Each control dimension is encoded and transmitted using the industry standard MIDI protocol to allow the instrument to interface with a large variety of synthesizers to control different parameters of the synthesis algorithm in real time, allowing for a high degree of expressiveness not possible with existing electronic wind instrument controllers. The first part of the thesis will provide a justification for the design of a novel instrument, and present some of the theory behind pitch representation, encoding, and transmission with respect to digital systems. The remainder of the thesis will present the particular design and explain the workings of its various subsystems

Development of a Low-cost Hybrid Music Synthesizer

Until recently, affordable music equipment has always been seen as “budget”, providing a poor user experience. Inexpensive equipment was plagued with audible noise, signal integrity issues, and convoluted user interfaces. Companies like Teenage Engineering have proven that this does not have to be the case, in 2019 introducing their Pocket Operator” series for $89. Due to the modern availability of low cost, high quality, consumer off the shelf [COTS] analog and digital components as well as creative engineering, the quality of inexpensive audio equipment has increased significantly. Despite these industry advances, the market is relatively small and shows a great potential for growth. This senior project capitalizes on this market possibility, providing a low-cost analog/ digital hybrid synthesizer architecture without the aforementioned caveats of poor signal integrity, user interface and sound quality. The synthesizer provides a low latency, simple to use, visual interface to the user. This visual interface allows intuitive and simple-to-learn access to the synthesizer’s parameters. The value of these parameters can also be loaded or saved from non-volatile memory. The power will be provided locally by a battery. Therefore, the synthesizer’s power draw will be low enough to ensure a significant on-time. Physically, the synthesizer provides industry standard audio connectivity to be interfaced with the end user’s existing equipment

Analog Violin Audio Synthesizer

Abstract In the past decade, music electronics have almost completely shifted from analog to digital technology. Digital keyboards and effects provide more sound capabilities than their analog predecessors, while also reducing size and cost. However, many musicians still prefer analog instruments due to the perception that they produce superior sound quality. Many musicians spend extra money and accommodate the extra space required for analog technologies instead of digital. Furthermore, audio synthesizers are commonly controlled with the standard piano keyboard interface. Many musicians can perform sufficiently on a keyboard, but requiring a specific skill set limits the size of the market for a product. Also, when reproducing instruments such as a violin, a keyboard will not suffice in simulating a controllable vibrato from a fretless fingerboard. There is a need for an interface that allows the user to successfully reproduce the sound of the desired instrument. The violin is just one example of instruments that cannot be completely reproduced on a keyboard. For example, cellos, trombones and slide guitars all have features that a keyboard cannot simulate in real time. The Analog Violin Synthesizer uses oscillators and analog technology to reproduce the sound of a violin. The user controls the synthesizer with a continuous touch sensor, representing the fretless violin fingerboard. The continuous interface allows for a violin sound played as a standard note, or a warmer sound with adjustable vibrato, based on how the user moves his or her hand. This product provides an innovation and next step to the use of analog technology in sound synthesis. However, as digital technology continues to improve, this product could potentially cross over into digital, with the continued use of the touch interface. Currently, there are products that utilize touch input, however they are often used for sound effects, and atmospheric sounds. Rarely are they used to allow for the digital playability of a synthesized acoustic instrument

Standalone Wireless Humming Music Synthesizer (HumSynth)

The HumSynth is a voice controlled music synthesizer. Unlike the commonly found voice modulators on the market, this product uses a vocal input in place of the traditional keyboard interface. This allows the instrument to serve as an intuitive learning tool for those not proficient in music theory. By using their voice, the consumer is able to get a feel for different scales and keys additionally bypassing the physical learning curve of learning a traditional instrument. By the date of submission this project performs basic functions in recreating the pitch input but does not meet the full specs. The enclosure is in its initial stages of design with several iterations of prototypes needed before the final configuration is selected

Exploration of Audio Synthesizers

In this creative component, I explore how synthesizers originated as well as the various techniques available for complex signal generation. The primary synthesis techniques researched were Additive, Subtractive, Frequency Modulation, and Sample-Based Synthesis. After extensive background information was examined, a series of MATLAB scripts were created to verify the synthesis implementation and demonstrate understanding. Following this, I set out to design my own hybrid synthesizer using a combination of the various techniques learned. The synthesizer created is a polyphonic composition device capable of audio generation as well as audio manipulation. It demonstrates core principles from each of the researched techniques to enable endless possibilities for the user. In the following pages, I explain the development process underwent to create this device and the details behind the unique designs

Prediction of the Spectrum of a Digital Delta–Sigma Modulator Followed by a Polynomial Nonlinearity

This paper presents a mathematical analysis of the power spectral density of the output of a nonlinear block driven by a digital delta-sigma modulator. The nonlinearity is a memoryless third-order polynomial with real coefficients. The analysis yields expressions that predict the noise floor caused by the nonlinearity when the input is constant