Eureka! Institutional Repository

This audio digital preamplifier and sound processor device is designed with one goal in mind: the best possible sound quality regardless of the total unit cost or its complexity. This device offers various inputs: 3 analog, 4 digital (2 electrical and 2 optical) and one Bluetooth. The analog inputs are converted to 24bit/96KHz digital signal using a digital-to-analog converter. The selected digital or converted analog audio signal, which follows the I2S protocol, is then processed by a dsp processor (minisharc by miniDSP). For digital inputs with varying sampling frequencies, an ASRC (asynchronous sample rate converter) adjust them to a 96KHz sample rate frequency. The dsp processor unit can operate at 48KHz or 96KHz sample rate frequencies and I have chosen to operate it at 96KHz. This dsp processor unit is equipped with four I2S outputs, each connected to a digital-toanalog converter, resulting in 8 available analog outputs. It can perform various tasks on each output independently, such as applying IIR and/or FIR filters, adding delays and adjusting the gain. In order to maintain the best sound quality, I opted to have the master sound level controlled by a digitally controlled analog potentiometer integrated circuit rather than the DSP. Users can select inputs or adjust the volume using the unit buttons and knob or via an infrared remote control. The selected input and volume in dB are displayed on the oled screen on the device. The various functions of the device are controlled by an STM32 microprocessor.