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Unformatted text preview: Digital 5 Band Equalizer Electrical Engineering 113D Instructor: Professor Jain TA: Rick Lan Spring 2006 June 6, 2006 Authors Michael Kim – 103109105 Gordon Tsui - Introduction and Background Digital signal processing is widely used in audio processing, which is the processing of a representation of audio signals and sounds. For this project, we dealt with the audio process of equalization. Equalization is defined as the process of modifying the frequency envelope of sound and to adjust the frequency response of an audio device. This process is achieved through the use of various filters. These filters include a combination of low pass, band pass and high pass filters. With the combination of these filters, we were able to isolate certain frequencies in the audio waveform, keeping the range of frequencies we desired and eliminating those undesired. To be more precise, for our project, a 5-band equalizer was implemented through the use of a single low pass filter, three band pass filters and a single high pass filter. In order to implement our equalizer using DSP, we were first required to design digital finite impulse response filters (FIR) using MATLAB. FIR filters operate on a basis of samples rather than a continuous signal, which makes it very easy to configure different filters with DSP implementation. Basically, by just changing the coefficient values, we were able to modify and create the low pass, band pass and high pass filters needed for our project. These coefficients were then quantized and assembly code was written to implement difference equations associated with them. The input for our sampled data values would be from the AC01 and the output would be sent through the D/A converter found on the AC01. Our input was an analog signal, which was converted through the A/D converter and then fed into the DSP. From there the filters were applied and then fed through the D/A converter where the output was analyzed. Project Development Step 1 – Materializing Ideas The first stage of the project development was finding a topic to use for our project. In looking over the various experiments and topics covered in the beginning weeks of the class, we decided to model our project from the digital filtering experiment. For that experiment, it only dealt with the implementation of a low pass filter, but with the knowledge of changing filters through the modification of coefficient values, we were able to apply that knowledge and extend it to create digital sound equalization. Step 2 – Implementations of FIR Filters Through the use of the fdatool found in MATLAB, we were able to create the desired filters for our project. Since we decided on creating a 5-band equalizer, we needed to design a low pass, three band pass and high pass filter. The original specifications for these filters were as follows: Filter Type Frequency Range Low Pass 0-2kHz Band Pass 1 2kHz-4kHz Band Pass 2 4kHz-7kHz Band Pass 3 7kHz-10kHz High Pass 10khz and above But in being restricted in having a ripple of 1dB, changes were made in the...
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