Audio Spectrum

Most of the Hi-Fi audio systems come with a fantastic display that provide music listeners with cisual representation of sound data that shows the strength of different frequencies of the music.These systems use bandpass filters to detect peak valuea at different frequencies. There are multipl ways to implement the audio spectrum function:

Figure 1: Frequency Spectrum Analyzer Display as Typically Seen on a Hi-Fi Audio System

Analog Filter
The Op-Amp can be designed to create a hardware analog bandpass filter as shown in Figure 2. Several components, such as capacitors and resistors are needed to design a one-band filter. Therefore, the Op-Amp circuit will need more PCB space to implement a multiband audio spectrum system.

Figure 2: Bandpass Filter Circuit
Audio IC (Integrated Circuit)
Semiconductor manufacturers have some audio spectrum Analyzer ICs on the market. One of the chips that is easy to use is the MSFEQ7. It is a seven-band graphic equalizer COMS chip and all it takes is just a few extra components to build a seven-band spectrum. The circuit diagram is shown in Figure 3.

Figure 3: MSGEQ7 Circuit Diagram
Digital Filter
A digital filter uses a digital processor to perform numerical calculations on sampled values of the signal. The analog input signal must first be sampled and digitized using an ADC (Analog to Digital Converter). The resulting binary numbers are transferred to the microprocessor, where numerical calculations are performed. A block diagram for the basic digital filter is shown on Figure 4.

Figure 4: A Block Diagram of a Basic Digital Filter

The AUDIOSPECTRUM object is used for making a simple spectrum Analyzer with a PSoC 5LP. It uses software algorithm to divide the input audio spectrum into 7 bands, 63Hz, 160Hz, 400Hz, 1KHz, 2.5KHz, 6.25KHz and 16KHz. The "AudioSpectrum" object needs to be linked with the following PSoC components: OPAMP, ADC-SAR, Interrupt, and 48KHz Clock signal. The default CPU frequency for PSoC 5LP is 24MHz. It is too slow to handle the heavy computation for the digital filter, so you need to increase the CPU frequency to 67MHz or 80MHZ (the maximum frequency is based on the PSoC 5LP chip that your board offers). You can read this article to understand how to change the CPU frequency.

EZ-PSoC LIB API

Example 1: Audio Spectrum Analyzer Using Microphone

Audio Spectrum Analyzer Using Microphone Device and LCD Display Module

This example will show you how to use AUDIOSPECTRUM object to build an Audio Spectrum Analyzer.

Required Hardwares

You have to prepare the following hardware (or compatible devices):

Electret Microphone:
- Electriet Microphone Amplifier with Auto Gate Control: Adafruit or
- Electriet Microphone Amplifier with Adjustable Gain: Adafruit
Character LCD display module:
- Standard LCD 20x4 - White on Blue: Adafruit

PSoC Components and Configuration

Double-click on TopDesign.cysch in the Workspace Explorer, drag-and-drop the following PSoC Components from the Component Catalog into your TopDesign.cysch schematic file, then configure each component's parameters to modify the behavior. For more information, refer to each component's datasheet, available from the Configure dialog, the Component Catalog, or from the Datasheets tab in the Workspace Explorer.

OPAMP: (Analog→Amplifiers→Opamp)
ADC_SAR: (Analog→ADC→SAR ADC)
ISR_ADC: (System→Interrupt)

Clock_1: (System→Clock)
LCD: (Display→Character LCD)
MIC: (Ports and Pins→Analog Pin)

Opamp

Double-click on Opamp_1 component, change its name to "OPAMP", set the Mode to "Follower" mode and Power to "High Power".

opamp

Pin Assignments

You can use the Pins tab of the Design-Wide Resources (DWR) window to assign a Pin Component to a physical pin. Figure 6 shows two assigned pins for EagleSoC board: P6[6:0] is assigned to LCD Port and P3[0] is assigned to MIC.

If you use an EagleSoC Mini board, you can assign P2[6:0] to LCD Port and P3[0] to MIC.
If you use a Cypress CY8CKIT-059 Prototyping board, you can assign P12[6:0] to LCD Port and P3[0] to MIC.

pins assignment
Figure 6: Pin Assignment in DWR Windows (for EagleSoC Board)

PSoC Creator will automatically assign pins if the user does not choose any, but this may lead to a pin placement that is more difficult to route on a PCB.

Clock Setting

Before the code initializes and starts the ADC_SAR component, the clock signal that is used to trigger the ADC_SAR must be disabled. It is controlled by the Start On Reset option in the Design-Wide Resources editor. This setting is enabled by default. Uncheck the Start On Reset option for CLOCK_ADC component as shown in Figure 7.

Figure 7: Uncheck the Start On Reset option on CLOCK_ADC

Wiring and Result

In this example, the output from the microphone has a DC bias, so it can be easily used with PSoC 5LP Analog/Digital Converter. Connect the output pin to the Port3 [0] (the pin you assigned in the previous page)

Figure 8: MAX9814 Wiring Diagram

Connect the 20x4 character LCD display module on the Port x[6:0] that you assigned. Build your project, upload the firmware to your PSoC 5LP board, play a music closely to the microphone, then you will see the spectrum on the LCD screen. You can read this article about the LCD display module.

Figure 9: The Signal Strength on the LCD Screen

Source Code

In the main source code (main.c), you need to create, configure and initialize objects using the EZ-PSoC LIB before the for loop. In your for loop, you have to check status using AUDIOSPECTRUM_IsDataReady(obj) function. If data is available, it will return TRUE value and then filter values will display as vertical bars. You can see the signal strength in the varying frequency on your LCD screen.

#include <project.h>
#include "ezCOMM.h"
#include "ezADCSAR.h"
#include "AudioSpectrum.h"

PEZOBJ_ISR              isr;
ISR_VECTOR(isr, ISR_ADC);
PEZOBJ_ADCSAR           adc;
PEZOBJ_AUDIOSPECTRUM    aud;

int main()
{

    isr = ezISR_Create();
    CONNECT_ISR(isr, ISR_ADC);

    adc = ezADCSAR_Create();
    CONNECT_ADCSAR16(adc, ADC_SAR);
    ezADCSAR_ConnectISR(adc, isr);
    ezADCSAR_Start(adc);

    aud = AUDIOSPECTRUM_Create();
    AUDIOSPECTRUM_ConnectADCSAR(aud, adc);
    AUDIOSPECTRUM_Start(aud);

    LCD_Start();
    LCD_ClearDisplay();
    LCD_Position(0,7); LCD_PrintString("Audio");
    LCD_Position(1,8); LCD_PrintString("Spectrum");

    OPAMP_Start();
    CLOCK_ADC_Start();
	CyGlobalIntEnable; /* Enable global interrupts. */
    /* Place your initialization/startup code here (e.g. MyInst_Start()) */

    for(;;)
    {
        /* Place your application code here. */
        if ( AUDIOSPECTRUM_IsDataReady(aud)){
            LCD_DrawVerticalBG(3,0,4,aud->ezFilter[0] );
            LCD_DrawVerticalBG(3,1,4,aud->ezFilter[1] );
            LCD_DrawVerticalBG(3,2,4,aud->ezFilter[2] );
            LCD_DrawVerticalBG(3,3,4,aud->ezFilter[3] );
            LCD_DrawVerticalBG(3,4,4,aud->ezFilter[4] );
            LCD_DrawVerticalBG(3,5,4,aud->ezFilter[5] );
            LCD_DrawVerticalBG(3,6,4,aud->ezFilter[6] );
        }
        CyDelay(50);
    }
}

/* [] END OF FILE */