School of Engineering and Applied Sciences EE113D: DSP Design Fall 2006.

School of Engineering and Applied Sciences

EE113D: DSP Design Fall 2006

http://www.ucla.edu/

Audio Processing:

EE113D: DSP DesignEarvin Caceres

Warren Tsu

Fall 2006

Valve Pre-Amp Filter




Project Specifications

Design a non-linear DSP transfer algorithm that will clip an analog input beyond a processing threshold to produce an adjustable pre-amp distortion

A/D

D/A

Anti-Aliasing Filter

Smoothing Filter

DSP Chip

TLC320AC01 AIC

OverdriveAssemblyAlgorithm

Analog Input

Amplified Output

DSKplus ChipsetAssembly Program



Clipping




Standards and Applications

Standards:• Universal 5-V power

supply• Standard 1/8” RCA

mini-jack• 8-bit bidirectional

parallel port• ‘AC01 analog

interface

Cell phones

Portable playersSoftware

Guitar Amps




Distortion Theory & DSP Clipping

Distortion arises when a signal changes in characteristic from the original waveform.

In DSP, clipping occurs when the signal is exceeds beyond the range of binary representation and is truncated.

Filter Effects on Signal Integrity




Hard vs. Soft Clipping & Timbre

Non-linear effects on timbre:•Increase in harmonic content•Sustain or compression

A DSP Amplifier is versatile with programmable performance.

Three Clipping Devices:1. Tube (Valve) Amplifier2. IC (Solid State) Amplifier3. DSP Amplifier Model




Valve Distortion Algorithm

• Amplify input signal• Test sign of input

signal• Add nonlinear

element for negative input

• Subtract nonlinear element for positive input

MATLAB Sinusoidal exampley = a * x + b * x ^ 2



DSP Assembly Implementation

cmps(a, *ar2) if (TC) goto neginput

goto posinput..

neginput b = *ar3 * *ar3 a = *ar1 * #2

a = a + b goto send.

Compares MSW and LSW in a

Sets flag TC. 0 if MSW is bigger. 1 otherwise

Nonlinear distortion factor

Add distortion

Amplify input signal



Design Problems and Lessons Learned

• Excessive Distortion– Original signal characteristics lost

• Arithmetic operations in assembly– Multiplication and Division using bit shifting

• Coding Strategies– Use incremental Development



Results

DEMO




References• http://www.uaudio.com/webzine/2005/october/index2.html• http://tons-of-tone.tripod.com/non_lin1.html• http://www.trueaudio.com/at_eetjlm.htm• http://en.wikipedia.org/wiki/Guitar_effects• http://en.wikipedia.org/wiki/Distortion• http://en.wikipedia.org/wiki/Clipping_%28audio%29• http://users.chariot.net.au/~gmarts/ampsmain.htm

http://www.uaudio.com/webzine/2005/october/index2.html

http://tons-of-tone.tripod.com/non_lin1.html


School of Engineering and Applied Sciences EE113D: DSP Design Fall 2006.

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