Audio Effects The NimTick FX Box

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Audio EffectsThe Nim-Tick FX Box

• Tim Olson
• Nick Szarzak
• ECE 345

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Objectives

• Implement eight audio effects on a DSP
• Phaser
• Flanger
• Chorus
• Reverb
• Delay
• Echo
• Distortion
• Equalizer

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Objectives cont.

• Create an easy to use graphical interface to
  control the effects parameters
• Successfully allow communication between the DSP
  and interface

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System Overview
DSP
Input Device
Amplifier
Speaker
PC
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Initial Plan

• Implement equalizer using bandpass filters
• Implement flanger and chorus using time varying
  delay lines
• Implement phaser using a time varying allpass
  filter
• Implement delay and echo using delay lines
• Implement reverb using comb and allpass filters
• Implement distortion using a look-up table
• Implement user interface in Matlab

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DSP Implementation

• Effects were implemented on a
• TI TMS320C54x DSP

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Equalizer

• Five band equalizer using one low pass filter and
  four bandpass filter
• Band 1
• 0-200HZ
• Band 2
• 200Hz-1KHz
• Band 3
• 1KHz-4Kz
• Band 4
• 4KHz-10KHZ
• Band 5
• 10KHz-15KHz

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Band 1 (0-200Hz)
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Band 2 200Hz-1KHz
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Band 3 1KHz-4KHz
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Band 4 4KHz-10KHz
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Band 5 10KHz-15KHz
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Block Diagram
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Delay

• One tap delay
• Variable length from 0 sec to 1.1 sec (49152
  samples)
• External memory on DSP board to accommodate large
  amount of data

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Block Diagram
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Echo

• Variable length from 0 sec to 1.1 sec (49152
  samples)
• External memory on DSP board to accommodate large
  amount of data

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Block Diagram
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Chorus

• Time varying delay ranging from 0 ms to 371 ms
• External memory on DSP board to accommodate large
  amount of data
• Time varying delay creates a detuning effect that
  is mixed with the original signal

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Block Diagram
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Flanger

• Time varying delay of 0 ms to 5.8 ms
• Short delay creates notches in the frequency band
  when phase shift is at 180 degrees

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Derivation of flangers frequency response
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cont.
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Block Diagram
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Phaser

• Uses an time varying allpass filter
• Allpass filter delay goes from 0 ms to 5.8 ms
• Phasing effect results from the signal with an
  altered phase from the allpass filter interfering
  with the input signal

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Block Diagram
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Allpass Filter
The delays in the filter change over time, which
creates the sweeping of notches in the frequency
band.
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Allpass cont.
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Reverb

• Used four comb filters and two allpass filters to
  create effect

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Delay Lengths

• Comb filter 1
• Delay length of 11.6ms (512 samples)
• Comb filter 2
• Delay length of 23.2ms (1024 samples)
• Comb filter 3
• Delay length of 46.4ms (2048 samples)
• Comb filter 4
• Delay length of 92.8ms (4096 samples)
• Allpass filter 1
• Delay length of 5.8ms (256 samples)
• Allpass filter 2
• Delay length of 11.6 (512 samples)

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Block Diagram
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Comb Filter
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Distortion

• Used hard clipping in order to achieve distortion
  effect
• The signal was shifted left until it overflowed
  then shifted back right to control the volume

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Interface

• The interface was implemented using Matlab
• The interface communicates with the DSP via the
  PC serial port
• Sliders and checkboxes were used to control the
  parameters

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Successes

• Implemented all planned effects on DSP
• Implemented interface with all planned parameters
• Successful communication with interface
• High quality interface and effects

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Challenges

• Communication of multiple words over the serial
  port
• Memory limitations
• Problems with varying delays

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If we had more time?

• Optimize assembly code and memory usage
• Develop hardware interface to eliminate the need
  for a PC
• Experiment with other algorithms for distortion

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Questions?
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Thank You