University of Victoria
Department of Electrical Engineering
Electronics 484 – Audio Signal Processing Assignment #5
Non-Linear Processing and Spatial Effects
Overdrive, Distortion, Fuzz, Exciter vs. Shelving Filter
Spatial Effects/Stereo Panning
Name: Oliver Hung – 02-29696
Report Submitted on: June 23, 2005
PART 1 – Sampling, Aliasing and Oversampling
1.1 – Matlab Waveform View: 1KHz Sine, 8KHz Sampling
1KHz Sine Wave Input, 8KHz Sampling Frequency
Time Domain View: Unprocessed, Squared and Cubed
1
0.8
0.6
Amplitude
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0
0.005
0.01
0.015
Time (s)
Squared 1KHz Sine Wave, 8KHz Fs
Cubed 1KHz Sine Wave, 8KHz Fs
1
0.8
0.6
0.8
0.6
0.4
0.7
0.4
0.2
0.6
0.2
0
-0.2
Amplitude
1
0.9
Amplitude
Amplitude
Unprocessed 1KHz Sine Wave, 8KHz Fs
1
0.8
0.5
0.4
0
-0.2
-0.4
0.3
-0.4
-0.6
0.2
-0.6
-0.8
0.1
-0.8
-1
0
0.005
0.01
0
0
0.015
0.005
Time (s)
0.01
-1
0
0.015
0.005
Time (s)
0.01
0.015
Time (s)
1.2 – Matlab Spectral View: 1KHz Sine, 8KHz Sampling
1KHz Sine Wave Input, 8KHz Sampling Frequency
Spectral View: Unprocessed, Squared and Cubed
4
3.5
3
Amplitude
2.5
2
1.5
1
0.5
0
0
500
1000
1500
2000
Frequency (Hz)
Unprocessed 1KHz Sine Wave, 8KHz Fs
2500
3000
Squared 1KHz Sine Wave, 8KHz Fs
4
4
3.5
3.5
3
3
2.5
2.5
3500
4000
Cubed 1KHz Sine Wave, 8KHz Fs
2
1.8
1.6
2
Amplitude
Amplitude
Amplitude
1.4
2
1.5
1.5
1
1
0.5
0.5
1.2
1
0.8
0.6
0.4
0
0
500
1000
1500 2000 2500
Frequency (Hz)
3000
3500
4000
0
0
0.2
500
1000
1500 2000 2500
Frequency (Hz)
3000
3500
4000
0
0
500
1000
1500 2000 2500
Frequency (Hz)
3000
3500
4000
1.3 – Matlab Waveform View: 2.5KHz Sine, 8KHz Sampling
2.5KHz Sine Wave Input, 8KHz Sampling Frequency
Time Domain View: Unprocessed, Squared and Cubed
1
0.8
0.6
Amplitude
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0
0.005
0.01
0.015
Time (s)
Square 2.5KHz Sine Wave, 8KHz Fs
Cubed 2.5KHz Sine Wave, 8KHz Fs
1
0.8
0.6
0.8
0.6
0.4
0.7
0.4
0.2
0.6
0.2
0
-0.2
Amplitude
1
0.9
Amplitude
Amplitude
Unprocessed 2.5KHz Sine Wave, 8KHz Fs
1
0.8
0.5
0.4
0
-0.2
-0.4
0.3
-0.4
-0.6
0.2
-0.6
-0.8
0.1
-1
0
0.005
0.01
-0.8
0
0
0.015
0.005
Time (s)
0.01
-1
0
0.015
0.005
Time (s)
0.01
0.015
Time (s)
1.4 – Matlab Spectral View: 2.5KHz Sine, 8KHz Sampling
2.5KHz Sine Wave Input, 8KHz Sampling Frequency
Spectral View: Unprocessed, Squared and Cubed
4
3.5
3
Amplitude
2.5
2
1.5
1
0.5
0
0
500
1000
1500
2000
Frequency (Hz)
Unprocessed 2.5KHz Sine Wave, 8KHz Fs
2500
3000
Squared 2.5KHz Sine Wave, 8KHz Fs
4
4
3.5
3.5
3
3
2.5
2.5
3500
4000
Cubed 2.5KHz Sine Wave, 8KHz Fs
2
1.8
1.6
2
Amplitude
Amplitude
Amplitude
1.4
2
1.5
1.5
1
1
0.5
0.5
1.2
1
0.8
0.6
0.4
0
0
500
1000
1500 2000 2500
Frequency (Hz)
3000
3500
4000
0
0
0.2
500
1000
1500 2000 2500
Frequency (Hz)
3000
3500
4000
0
0
500
1000
1500 2000 2500
Frequency (Hz)
3000
3500
4000
1.5 – Matlab Waveform View: 2.5KHz Sine, 16KHz Sampling
2.5KHz Sine Wave Input, 16KHz Sampling Frequency
Time Domain View: Unprocessed, Squared and Cubed
1
0.8
0.6
Amplitude
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0
1
2
3
4
Time (s)
6
Squared 2.5KHz Sine Wave, 16KHz Fs
Cubed 2.5KHz Sine Wave, 16KHz Fs
1
0.8
0.6
0.8
0.6
0.4
0.7
0.4
0.2
0.6
0.2
-0.2
Amplitude
1
0.9
0
0.5
0.4
0
-0.2
-0.4
0.3
-0.4
-0.6
0.2
-0.6
-0.8
0.1
1
2
3
4
Time (s)
5
6
7
-0.8
0
0
8
8
-3
1
-1
0
7
x 10
0.8
Amplitude
Amplitude
Unprocessed 2.5KHz Sine Wave, 16KHz Fs
5
1
2
-3
x 10
3
4
Time (s)
5
6
7
-1
0
8
1
2
-3
x 10
3
4
Time (s)
5
6
7
8
-3
x 10
1.6 – Matlab Spectral View: 2.5KHz Sine, 16KHz Sampling
2.5KHz Sine Wave Input, 16KHz Sampling Frequency
Spectral View: Unprocessed, Squared and Cubed
4
3.5
3
Amplitude
2.5
2
1.5
1
0.5
0
0
1000
2000
3000
Cubed 2.5KHz Sine Wave, 16KHz Fs
4000
Frequency (Hz)
5000
6000
Cubed 2.5KHz Sine Wave, 16KHz Fs
4
4
3.5
3.5
3
3
2.5
2.5
7000
8000
Cubed 2.5KHz Sine Wave, 16KHz Fs
2.5
2
1.5
Amplitude
Amplitude
Amplitude
2
2
1.5
1
1
0.5
0.5
1.5
1
0.5
0
0
1000
2000
3000 4000 5000
Frequency (Hz)
6000
7000
8000
0
0
1000
2000
3000 4000 5000
Frequency (Hz)
6000
7000
8000
0
0
1000
2000
3000 4000 5000
Frequency (Hz)
6000
7000
8000
1.7 – Oversampling Discussion
From the above screen shots, we can see that the 1KHz sine wave has no problem even
after it has been cubed. However, it is clear that the 2.5 KHz sine wave is experiencing
significant aliasing with an 8KHz sampling rate. In fact, from the 2.5KHz power spectra,
we can see that the cubed waveform is missing a harmonic, (the graph does not even
extend that far!) at about 7500Hz. Once we use 16KHz as a sampling frequency we can
see that much of the aliasing disappears, (although the squared and cubed 2.5KHz sine
waves are still a little distorted). However, the power spectra of the cubed wave does
clearly show the 7500Hz harmonic as expected.
PART 2 – Overdrive, Distortion and Fuzz
2.1 – Audigy Waveform View of Unprocessed Guitar.wav
2.2 – Audigy Spectral View of Unprocessed Guitar.wav
2.3 – Audigy Waveform View of Overdriven Guitar.wav
2.4 – Audigy Spectral View of Overdriven Guitar.wav
2.5 – Audigy Waveform View of Distorted Guitar.wav
2.6 – Audigy Spectral View of Distorted Guitar.wav
2.7 – Audigy Waveform View of Fuzzy Guitar.wav
2.8 – Audigy Spectral View of Fuzzy Guitar.wav
2.9 – Discussion of Non-Linear Effects
This section was pretty straightforward since the code was based directly on that found in
the book. I did however, add a gain to the overdrive effect to make it more
prominent/obvious. (There normally is a gain knob on overdrive effects boxes/pedals.)
The distortion and fuzz effects turned out pretty much as expected.
PART 3 – Exciter versus High-Shelving Filter
3.1 – Audigy Waveform View of Unprocessed Flute.wav
3.2 – Audigy Spectral View of Unprocessed Flute.wav
3.3 – Audigy Waveform View of Excited Flute.wav
3.4 – Audigy Spectral View of Excited Flute.wav
3.5 – Audigy Waveform View of High-Shelved Flute.wav
3.6 – Audigy Spectral View of High-Shelved Flute.wav
3.7 – Discussion of Exciter and High-Shelf Filter
The distortion added to the high frequencies produces the exciter effect. The exciter
effect serves to brighten up the sound without causing the shrillness that the highfrequency shelving filter causes. (Produces a slightly “metallic” sound as opposed to a
sharp/shrill sound.) I set the exciter and high-frequency shelving filter to the same cutoff
frequency of 1500Hz since the fundamental and first couple of harmonics were well
below that frequency.
PART 4 – Spatial Effects (Stereo Positioning)
4.1 – Audigy Waveform – 100% Left Audio – Delay Based
4.2 – Audigy Waveform – 50% Left Audio – Delay Based
4.3 – Audigy Waveform – Centered Audio – Delay Based
4.4 – Audigy Waveform – 50% Right Audio – Delay Based
4.5 – Audigy Waveform – 100% Right Audio – Delay Based
4.6 – Audigy Waveform – 100% Left Audio – Amplitude Based
4.7 – Audigy Waveform – 50% Left Audio – Amplitude Based
4.8 – Audigy Waveform – Center Audio – Amplitude Based
4.9 – Audigy Waveform – 50% Right Audio – Amplitude Based
4.10 – Audigy Waveform – 100% Right Audio – Amplitude Based
4.11 – Discussion of Spatial Effects
The two methods for implementing stereo positioning were relatively simple to program.
However, identifying what delay or amplitude was required to produce the 50% left or
right sound, was very, very difficult. I actually produced delays from 0ms to 1ms in
0.005ms intervals and spent a long time listening to them using speakers, earphones and
headphones. I am still uncertain what the “correct” values should be. My best guess is
that a 0.3-0.5ms delay is sufficient to create a “completely from the left or right” sound.
Increasing the amount of delay continues to move the sound further to the extremes,
however, I find that sound begins to “break apart” sounding like there is too much
reverb. For the 50% sound placements, my best guess would be somewhere between
0.025ms to about 0.05ms, (the screenshot above is using 0.03ms delay). As for the
amplitude based positioning, a drop of 30dB produces a 100% left/right sound. For the
50% sound positioning, a 5dB to 7dB drop is sufficient. These values again, are my
“best subjective guesses”.