AUDIO FILTERING WITH LED INTERFACING

•Microcomputer systems 1

•ECE 3551

•Dipesh Patel

What Does The Project DO?

Activating Filters using the pushbuttons.

Combination of LEDs turned on with each pushbutton pressed.

Explanation:

Pushbutton LEDs turned on

Filters Active

• PF8 pressed once LEDs 4,5,6 active Highpass 1 active

• PF8 pressed twice LEDs 7,8,9 active Lowpass 2 active

• PF8 pressed thrice No LED active No filter active

• PF9 pressed once LEDs 4,5,8,9 active Highpass 2 active

• PF9 pressed twice LEDs 6,7 active Lowpass 2 active

• PF9 pressed thrice No LED active No filter active

• PF10 pressed once All LEDs active Highpass 3 active

• PF10 pressed twice LEDs 5,8 active Lowpass 3 active

• PF10 pressed thrice No LEDs active No filter active

• PF 11 pressed once LEDs 4,6,7,9 active Bandpass active

• PF11 pressed twice No LEDs active No filter active

Designing Filters

Used Matlab to design Filters.

fdatool in the Matlab pops up the window for filters.

The filters were all chebyschev type II and the order that was specified was 8.

• The following is the module of a particular filter from Matlab.

Theory of filters:

𝒂𝑲𝒀𝑵𝒌=𝟎 ሾ𝒏− 𝒌ሿ= 𝒃𝑲

𝑴𝒌=𝟎 𝑿ሾ𝒏− 𝒌ሿ

𝒚[𝒏] = 𝒃𝑲𝒙𝑵𝒌=𝟎 ሾ𝒏− 𝒌ሿ− 𝒂𝑲

𝑴𝒌=𝟏 𝒚ሾ𝒏− 𝒌ሿ

The input x[n] and the output y[n] of an IIR filter satisfy the Nth order linear coefficient linear equation.

The first coefficient of the y[k] series is 1 and therefore the 2nd equation holds true.

Implementation of filters:

Transfer function is as follows:

The implementation takes place as follows:

2

21

1

22

110

1

zAzA

zBzBBzH

mdBmdBmdBmy

mdAmdAmxmd

012

12

12

12

2121 21210 myAmyAmxBmxBmxBmy

Process:

The filtering of audio signals take place in the process data.c file.

The filters are actually implemented in the process data.c file using the arrays for the filter coefficients.

The actual calling of the LEDs and pushbutton takes place in ISR.c file.

Interrupt handlers:

EX_INTERRUPT_HANDLER(FlagA_ISR).Sport0 RX ISR IVG 9

EX_INTERRUPT_HANDLER(Sport0_RX_ISR). FlagA ISR IVG 12

The 1st interrupt handler is caused when any of the pushbutton from PF8 to PF 11 is pressed.

The 2nd interrupt handler is caused when any of the audio signal is transferred through a buffer.

Codec Interaction with DSP

The SPI port is disabled after initialization. All the data transfer takes place through SPORT.

Make Sure!!!

Make sure that all the SW9 pins are on that enables the pushbuttons from PF8 – PF11.

We need to initialize the LEDs and the pushbuttons in order to use them.

The memory of LEDs should be set to 0x01 in order to use them as output.

Practical application:

This project can be used in an audio recording company.

They don’t need to buy amplifiers.

The signals can be amplified as desired using the Blackfin processor, the visual DSP software and matlab.

Questions?