Using DSP technology to improve sound quality in active speakers

Sammanfattning: Aditus Science has developed a system to improve the sound quality in speaker systems, using DSP technology. Software developed in MATLAB is being used to make measurements of the speakers via microphones. Based on those results, the parameters for the signal processing in the DSP can be set. A prototype model of the system was used as hardware when the software was developed. The system has several analog and digital inputs and outputs over SPDIF, Ethernet, 3.5mm analog stereo plug etcetera. An ADC converts the analog inputs to a digital signal in the format interintegrated circuit sound signal, i2s. The DSP makes signal processing of the digital audio stream to optimize it for the speaker and sends it to the amplifier through a DAC. The digital audio signals are also directly distributed over the Ethernet, the digital output connectors, and to the analog outputs through a DAC. The system is designed to be controlled by the user over a web server or from a front panel on the device. The main purpose of the thesis work is to develop the hardware platform to be used for the system. Three different PCBs were designed. One board hosting the digital parts, one the analog parts, and one backplane to connect the other two boards and to provide the power supply. The first board with the digital parts includes a DSP, an AVR to be microcontroller, a synthesizer and connectors for the digital inputs and outputs. The DSP is used for the signal processing of the audio signals, and is also used to handle inputs with different sample rates through the internal FARM, flexible audio routing matrix. The AVR micro controller unit is used as the master in the system. It loads the program and parameters into the DSP, ADC/DAC and the synthesizer. It handles the user interface from the front panel, and hosts the server with the user interface over Ethernet. The synthesizer is being used to tune the clock frequency to be able to counteract data drop if the audio stream over Ethernet has a slightly different frequency than the system. The board with the analog parts also includes some digital signals from the DSP, and control signals from the AVR to the ADC/DAC. The analog connectors are located in this board and also the input and output networks of operation amplifiers. The first part of the work was to make the schematics for the three cards, and the second part to make the layout. Special care was taken to make a system with as good performance as possible. An example of those parts is to carefully design ground planes and power planes to reduce noise and current loops. The placement of the components and the routing of the signals were carefully made to eliminate over hearing and noise introduced between the blocks. It also handles routing of differential pairs and impedance matching.