Introduction
You’ve just spent a large sum of money for that new stereo and it’s time to fine tune your listening environment with the graphic equalizer. But wait. How can you do that objectively? Hearing can be a subjective experience and very much dependent on the individual. What is needed is an objective analysis of the sound. The Audio Analyzer described in this article performs an error-free optimization of a stereo output from 20Hz to 20Khz.

Functional Description
The Audio Analyzer is composed of two primary functional blocks: the White Noise generator and the Spectral Analyzer. The white noise is fed into the left and right stereo inputs. The amplified noise from the speakers is then picked up by an on-board electret condenser microphone, which provides the signal to the Spectral Analyzer. The Spectral Analyzer measures the signal at 8 unique frequency bands in the audio spectrum and displays the results in a bar graph format. The Spectral Analyzer, White Noise Generator, and display decoder/driver were all implemented from a single Cypress Microsystems CY8C26443 PSoC chip

• Figure 1- Block Diagram of Audio Analyzer Setup

To use the instrument, the user runs a stereo patch cable between the RCA jacks on the side of the unit to an appropriate input on the rear of the amplifier under test. The stereo should then be turned on and the input selected. While standing in the desired listening location, turn the instrument on, and select the right channel. White noise should be heard from the speaker. The user should then adjust the equalizer settings on the amplifier until a flat response is observed on the display of the analyzer. This procedure is repeated for the left channel

Hardware Description
The schematic for the Audio Analyzer can be seen in Appendix A. The microphone is biased and fed into port P01. The amplified microphone signal is then output at P03 which is fed directly into P06 via a 100K resistor and to P04 through a 2Khz low pass filter.

The analog white noise signal is output at P02. This signal is mechanically switched by the user between two 20Khz low pass filters that feed RCA jacks for the right and left channels.

Two LiteON LED arrays are used to provide a multiplexed 8X8 bar graph display (two of the columns are not used). Port P2 is used to directly drive the rows while port P1 drives Q1 through Q8 for the column drive.

The power supply consists of a Linear Technology LT1300 switch-mode regulator which is used to boost two AA batteries to 5 volts.

All of the functionality for the Audio Analyzer takes place in the PSoC device. Figure 2 illustrates each of the blocks used within the chip for the analyzer.

• Figure 2 - Resource Utilization Map of PSoC Chip

A breakdown of the block usage is:

• White Noise Generator: DBA03, DCA04, DCA05, DCA06, DCA07, and ASB13
• Microphone Amplification: ACA00, and ACA01
• Programmable Bandpass Filter: ASA10, ASA21, ASB11, ASB20, DBA00, and DBA01
• A/D Conversion: DBA02, ACA02, ACA03, and ASA12
• General Purpose Timing: DCA06

The following sections provide a detailed description of the PSoC design: