Digital 5-Band Equalizer

Electrical Engineering 113D

Authors: Gordon Tsui

Michael Kim

Digital Equalizer

• Used in Audio Processing and is the process of modifying the frequency envelope of sound

• Found in various programs such as WINAMP, Windows Media Player and any other application that requires digital audio processing.

• Number of bands vary on each equalizer

Development

• Modeled project after Experiment 2

• Used MATLAB to obtain coefficients required for different filters

• Found impulse response to verify requirement needs

• Implemented assembly code and tested results

System Diagram

LOW PASS

BAND PASS

BAND PASS

BAND PASS

HIGH PASS

INPUT OUTPUT

Impulse Response

• Specifications needed to meet a 1dB Ripple

Filter Specifications

• Our Equalizer consisted of 5-bands

Low Pass 0-2kHz

Band Pass 1 1.6kHz-3.6kHz

Band Pass 2 4.2kHz-7.2kHz

Band Pass 3 7.7kHz-9.7kHz

High Pass 10.28khz and above

Filter Specifications

• Low Pass Filter – Magnitude Responses

0 5 10 15 20-160

-140

-120

-100

-80

-60

-40

-20

0

20

Frequency (kHz)

Mag

nitu

de (

dB)

Magnitude Response (dB)

Low Pass Filter Magnitude Response

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

0 500 1000 1500 2000 2500

Frequency (Hz)

Mag

nit

ud

e (d

B)

•Difference seen between two due to anti-aliasing filter in DSP Board

Filter Specifications

• Band Pass Filter 1 – Magnitude Responses

0 5 10 15 20-160

-140

-120

-100

-80

-60

-40

-20

0

20

Frequency (kHz)

Mag

nitu

de (

dB)

Magnitude Response (dB)

Band Pass Filter 1 Magnitude Response

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

0 1000 2000 3000 4000 5000

Frequency (Hz)

Mag

nit

ud

e (d

B)

Filter Specifications

• Band Pass Filter 2 – Magnitude Responses

0 5 10 15 20-160

-140

-120

-100

-80

-60

-40

-20

0

20

Frequency (kHz)

Mag

nitu

de (

dB)

Magnitude Response (dB)

Band Pass Filter 2 Magnitude Response

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

0 2000 4000 6000 8000 10000

Frequency (Hz)

Mag

nit

ud

e (d

B)

Filter Specifications

• Band Pass Filter 3 – Magnitude Responses

0 5 10 15 20-160

-140

-120

-100

-80

-60

-40

-20

0

20

Frequency (kHz)

Mag

nitu

de (

dB)

Magnitude Response (dB)

Band Pass Filter 3 Magnitude Response

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

0 2000 4000 6000 8000 10000 12000

Frequency (Hz)

Mag

nit

ud

e (d

B)

Filter Specifications

• High Pass Filter – Magnitude Responses

0 5 10 15 20-160

-140

-120

-100

-80

-60

-40

-20

0

20

Frequency (kHz)

Mag

nitu

de (

dB)

Magnitude Response (dB)

High Pass Filter Magnitude Response

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

0 2000 4000 6000 8000 10000 12000 14000 16000

Frequency (Hz)

Mag

nit

ud

e (d

B)

•Difference seen between two due to FHP cutoff frequency

Assembly CodeXGL .word 32767 ;the different gain valuesXGB .word 0 ;at the end of the .data section

A = trcv ; load accumulator with word

AR1=#XLP ; AR1 points to XLP and gets value of A*AR1=A

AR1=#XBP ;AR1 points to XBP and gets value of A*AR1=A

AR3 = #XNLAST ;points to XNLASTA = #0 ;sets value of A to 0repeat(#122) ;123 coefficientsMACD(*AR3-,L0,A) ;same as experiment 2*AR0 = hi(A) ;AR0 gets the MSB of AA=#0 ;sets value A to zeroMACP(*AR0, XGL, A) ;multiplies values of at AR0 and XGL and stores in A*AR0 = hi(A) ;AR0 gets the MSB of A

AR3 = #XNLASTBA = #0repeat(#122)MACD(*AR3-,B0,A)*AR4 = hi(A)A=#0MACP(*AR4, XGB, A)*AR4 = hi(A)

A = *AR0A = A + *AR4 ;the output of the two filters are added together

tdxr = A ;value of A sent to output

Problems With Assembly Coding

• Initially had too many coefficients that the DSP board couldn’t handle

• Unable to use the @ operator

• Gain of 1*(2^15-1) reduces signal by factor of 2

Examples

• Audio Clip with unity Gain

• Applied High Pass Filter

• Applied Band Pass Filters

• Combination of Band Pass and High Pass

• Applied Low Pass Filter