Audio Digital Equalizer 2/3 Octave Using OMAP-137 as the Signal Processor with digital

Pranjoto, Hartono and Suryadinata, Adrian (2014) Audio Digital Equalizer 2/3 Octave Using OMAP-137 as the Signal Processor with digital. AENSI Journals Australian Journal of Basic and Applied Sciences, 8 (14). pp. 7-12. ISSN 1991-8178

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Background: This project was about design and implementation of an audio digital equalizer with digital control using computer as the controller. The equalizer had 2/3 octave band separation resulting into 15 bands across the entire audio spectrum frequency and with left and right channel with total of 30 bands. The band separation was based on the well-known standard defined by IEC 61260/1260 year 1995, ISO 266 year 1997 and ISO 3 year 1973. This specification also incorporated the filter ± 3dB bandwidth for each filter band of the equalizer. The hardware to realize the equalizer was a special purpose digital signal processing system from Texas Instruments. The processor for the equalizer was the OMAP137 in the form of a development board. This system had several features which were very essential for digital signal processing such as fast central processing unit to process both integer and floating point numbers, embedded analog to digital converter (ADC), digital to analog converter (DAC) and universal asynchronous receiver/ transmitter (UART) to connect to a computer The main part of this equalizer was the bandpass filters to manage the frequency response of the digital equalizer based on the second order Butterworth with transfer function of H(s) = (s2+1)-1. The transformation of the filter from the analog s-plane into the digital z-plane used the bilinear Z-transform which had been shown to have stable cut-off characteristics across all frequency with different sampling frequency. The filter coefficients were computed and adjusted using sampling frequency of 48 kHz and 16- bit-ADC. Computation of the filters was implemented in 32-bit integer formats to expedite the results and ensure there is no overflow and then truncated back into 16-bit integer to match the capability of the 16-bit-DAC. All of the 15 channels of the filters were computed in parallel and checked for the characteristics of the filters as an equalizer as opposed to single bandpass filter. DSP system was also checked for the capability to perform all 15 channels of the equalizer and see if the resulting system works as desired. This design approached was for both channels and then tested together to ensure real-time performance for all filters with the sampling rate of 48 kHz. Visual control of the equalizer was via UART port of the system connected to a computer mimicking similar to the view of a graphic equalizer with few added buttons such as bypass, duplicate left-right channel, and undo. The setting can be downloaded into the DSP system and stored permanently so when the equalizer was turned on, it would be at the condition of the last setting. The output of the DSP system was observed and compared using controlled input and then observed to ensure the performance was similar to the calculated value. The final test was to observe the performance for each bandpass filter at each different audio channel with music using auditory observation. The overall system performance was also evaluated using common music and the audio output evaluated and compared with common equalizer and the result was very similar.

Item Type: Article
Uncontrolled Keywords: digital equalizer, digital signal processing, Texas Instrument, OMAPL137
Subjects: Engineering
Engineering > Electrical Engineering
Divisions: Journal Publication
Depositing User: Ir Hartono Pranjoto,Ph.D., IPU
Date Deposited: 19 Aug 2016 03:34
Last Modified: 19 Aug 2016 03:34

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