DSP PROJECT 5

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DSP PROJECT 5
Sound Processing FX Using MATLAB
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Outline
Effects implemented

• Phase Shifting
• Pitch Shifting
• - Raising (Chipmunk)
• - Lowering (Robotic)

• Ring Modulation
• Tremolo

• Flanging
• Chorusing

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Phase Shifting

• Creating one or more notches in the frequency
  domain
• that eliminate sounds at the notch
  frequencies.

• Notches are created by simply filtering the
  signal, and
• mixing the filter output with the input signal.

• The filters can be designed so that we can
  independently
• control the location of each notch, the
  number of notches,
• and even control the width of the notches.

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Input
Output
A simple sine wave (a), and the same signal with
a phase lag of (b) 90 degrees, (c) 180 degrees,
(d) 270 degrees, and (e) 360 degrees (one cycle
of the waveform). Note that when (a) and (c) are
added together, the result is zero - complete
cancellation.
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Pitch shifting

• Time Domain Granulation
• and subsequent reassembly

• Frequency Domain Vocoding or
• Analysis Re-synthesis Techniques
• to modify the sound.

• Reading the signal in at a
• constant speed and output the
• result at a different one.

• This is the same as re-sampling
• the output of our pitch changing
• algorithm.

• We do not scale our windows
• but move them in time.

Input
Lowered
Raised
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Ring modulation

• Takes two signals (each with some frequency),
  and produces
• a signal containing the sum and differences
  of those frequencies.

• Multiplication results in an output that
  contains notes at
• the sum and difference of the two input
  signal's
• frequencies.

• These frequencies will typically be
  non-harmonic, so
• the ring modulator can create some very
  dissonant sounds.
• For this reason, ring modulation is not a
  widely used effect.

• Sound produced is very dissonant and harsh.

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Inputs
Output

• 400 Hz sine wave, (b) 600 Hz sine wave, and
• (c) the product of the two (a 200 Hz and 1000 Hz
  sine wave
• added together). The product is zero when either
  wave is zero.

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Tremolo Effect

• Special case of ring modulation.
• RingMod CM (C and M are bi-polar)

• If Mlt20 Hz, amplitude of C varies at the rate
  of M.

• If 20HzltMlt20 kHz, for each sinusoidal
  component,
• we get a pair of sidebands in the output
  spectrum.

Inputs
Output
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Flanging Effect

• Characteristic sound that many people refer to
  as
• a "whooshing" sound, similar to the sound of a
  jet plane
• flying overhead.

• Mixing a signal with a slightly delayed copy of
  itself,
• where the length of the delay is constantly
  changing.

• Notches in the frequency response move
• around to produce the distinctive sloshing
  flange sound

• Frequency response is sometimes called a comb
  filter,
• as its notches resemble the teeth on a comb.

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Input
Output

• Frequency response of a simple flanger with two
  
• different delay times (both with a depth of
  1).
• The plot on the left would be for a flanger
  with a
• smaller delay than that on the right.

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Chorus Effect
Input
Output

• Adds some thickness to the sound, and is often
  described
• as 'lush' or 'rich.

• Delayed and pitch modulated copy of the input
  together
• with the original, we have the chorus effect

• Chorus differs from flanging in only a couple
  of ways

- Delay times in a chorus are larger than in a
flanger, usually somewhere between 20 ms.
and 30 ms. The flanger's delay usually
ranges from 1 ms. to 10 ms.
- There is generally no feedback used.
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References
http//www.harmony-central.com/Effects/effects-exp
lained.html
http//www.ai.mit.edu/people/jimmylin/writing/111l
ab3.pdf
http//users.iafrica.com/k/ku/kurient/dsp/links.ht
ml
http//www.helsinki.fi/ssyreeni/dsound/dsndc08