Electrical and Computer Engineering

1
Electrical and Computer Engineering
2
Overview

• Frequency
• Relationship to sound
• Relationship to pitch
• Filters
• Low Pass
• High Pass
• Band Pass
• Band Reject

3
Frequency, Sound Pitch

• Human audible range is
• approx. 20Hz 20,000Hz
• The pitch is a sounds relationship within the
  human audible frequency spectrum
• Higher frequency higher pitch
• Example Screeching nails on a chalkboard
• Lower frequency lower pitch
• Example Rumbling train passing by

4
Low Frequency
Looking at the graph below, you will see that
most of the frequency content in the audio sample
is centered around 102 Hz (100 Hz).
Play low frequency audio sample
5
High Frequency
Looking at the graph below, you will see that
most of the frequency content in the audio sample
is centered around 103 Hz (1000 Hz).
Play high frequency audio sample
6
Combination High and Low Frequency
Looking at the graph below, you will see the
summation of the audio samples.
Play combination frequency audio sample
7
Filter Types and Filter Parameters

• Types of Filters
• Low-Pass High-Pass
• Band-Pass Band-Reject
• Cut-off Frequency(s)
• Where to start/stop filtering
• Order of Filter
• Quality of drop-off
• Higher order more complexity

8
Low-Pass Filter

• Lower frequencies are passed and higher
  frequencies are rejected
• Example
• Cutoff frequency 10kHz Order 10

You wont likely hear anything below this
threshold
9
High-Pass Filter

• Lower frequencies are rejected and higher
  frequencies are passed
• Example
• Cutoff frequency 10kHz Order 10

10
Frequency Overlap
Although the concentration of frequency content
for the individual samples is toward the ends of
the spectrum, using a low-pass or a high-pass
filter on the combined sample will affect the
sound of BOTH instruments.
11
Band-Pass Filter

• Selected section of frequencies are passed and
  all other frequencies are rejected
• Example
• Cutoff frequencies 7.5kHz and 12.5kHz Order
  10

You wont likely hear anything below this
threshold
12
Band-Reject Filter

• Selected section of frequencies are rejected and
  all other frequencies are passed
• Example
• Cutoff frequencies 7.5kHz and 12.5kHz Order
  10

You wont likely hear anything below this
threshold
13
Frequency Overlap
When using a band-pass filter to pass just the
Sound, you will also be passing some parts of the
Piano Bass When using a band-reject filter to
eliminate just the Sound, you will also eliminate
some parts of the Piano Bass