3 Band Automatic Real-time Equalizer for Audio Amplifier Signal Correction
Author
Nielsen, Dennis Schmidt
Term
7. term
Education
Publication year
2014
Submitted on
2014-06-04
Pages
82
Abstract
This thesis addresses the problem of flattening the typically uneven frequency response of a tube amplifier by designing an automatic 3‑band real‑time equalizer. The system is implemented on a Xilinx FPGA using a MicroBlaze processor configured as a DSP‑like 5‑stage pipeline. Audio input is received via a VHDL‑built S/PDIF interface at CD quality (44.1 kHz, 16‑bit), and both output and feedback from the amplifier are handled through a Wolfson WM8731 audio CODEC, with all interface protocols implemented in VHDL to offload the processor. Equalizer and analyzer filters are based on standardized octave bands (low, mid, high), designed and discretized using the bilinear z‑transform (Tustin’s method) with pre‑warping, and realized as difference equations in C with interrupt‑driven real‑time processing. The system monitors band energy and adjusts per‑band gains in real time to approach an overall flat response. The report details the problem definition, hardware architecture, signal‑processing methods, software design and implementation, and testing setups and measurements; specific performance results are not included in this excerpt.
Dette specialearbejde undersøger, hvordan en rørforstærkers ofte ujævne frekvensrespons kan udjævnes ved hjælp af en automatisk 3-bånds realtids-equalizer. Systemet er udviklet på en Xilinx FPGA med en MicroBlaze-processor konfigureret som en DSP-lignende 5-trins pipeline. Lyd indlæses via en VHDL-implementeret S/PDIF-modtager i CD-kvalitet (44,1 kHz, 16 bit), og både udgang og feedback fra forstærkeren håndteres gennem en Wolfson WM8731 audio-CODEC, hvor alle interfaceprotokoller er implementeret i VHDL for ikke at belaste processoren. Equalizer- og analysefiltre er baseret på standardiserede oktavbånd (lav, mellem, høj), udregnet og diskretiseret med bl.a. bilineær z-transform (Tustins metode) med pre-warping, og realiseret som difference-ligninger i C med afbrytningsstyret realtidsbehandling. Systemet overvåger energien i hvert frekvensbånd og tilpasser båndgevinsterne i realtid for at nærme sig en flad samlet frekvensrespons. Rapporten beskriver problemformulering, hardwarearkitektur, signalbehandlingsmetoder, softwaredesign og implementering samt testopsætninger og målinger; konkrete resultater og ydelsestal fremgår ikke af det medtagne uddrag.
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