What is Sound? The Physics of Speech and Hearing

Daniel Bone Signal Analysis and Interpretation Laboratory Los Angeles, CA, USA

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Discussion • What is sound? • How do we hear sound? • What is speech?

• How is speech produced? • Are connections human speech and hearing connected? 2

Speech Production • Video that demonstrates speech production http://sail.usc.edu/span/

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Recording Speech with MRI

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Research in Speech Production • Why do researchers study speech production? 1. For the purely scientific question of answering why.

2. Understanding how people plan their speech can help us to understand the brain. 3. To understand proper speech production. Additionally understand how people can adapt. What if someone is missing part of their tongue, for example? 4. To improve computers ability to model speech- SiRi. 5

What is Sound? Demos: • Rubber bands of various sizes • Cup telephones (two cups connected by a taut string) • Tuning fork • What is sound? How can you describe it?

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What is Sound? • What is sound? How can you describe it? Sound is Vibration

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Two Types of Waves • What are the two types of waves? • Electro-magnetic: light, radio, communication, x-ray • E-M waves are electro-magnetic force-fields of energy travelling through space.

• Mechanical: earthquake, slinky wave, ocean wave • Mechanical waves are energy travelling through a medium (solid, liquid, gas)

• What type is sound (and speech)?

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Two Types of Waves • What are the two types of waves? • Electro-magnetic: light, radio, communication, x-ray • E-M waves are electro-magnetic force-fields of energy travelling through space.

• Mechanical: earthquake, slinky wave, ocean wave • Mechanical waves are energy travelling through a medium (solid, liquid, gas)

• What type is sound (and speech)? Sound is a mechanical wave

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How does sound travel? • Sound travels by pushing the air molecules into each other, creating areas of high pressure, and low pressure.

http://www.tellmewhyfacts.com/2007/09/how-doessound-travel.html

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Calculating Frequency • Freq = # cycles/ # seconds, Hertz is cycles/second • You hear 10 cycles of a signal in 5 seconds, what is the frequency of the signal?

• A adult’s pitch is 200 Hz. Is this likely a man or a woman? In 1 second, how many cycles would we hear?

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Frequency of Sound • What parts and properties of a wave have we learned? Frequency: the number of cycles received in a second Measured in- Hertz (Hz), cycles/second

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Sounds with multiple frequencies • What happens if two pure frequency (tone) signals add? They produce new sounds, that are a combination of the individual frequencies (tones). Speech is a combination of many frequencies, although some are the most important. The most important frequencies in a speech sound are called formant frequencies. They form the majority of the sound you hear. For example: The /ah/ sound has major frequencies of:

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Frequency of a tuning fork • A tuning fork has a nearly pure frequency (tone). Let’s measure it using Praat.

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Features of Speech

Pitch is only a single frequency Sound is composed of frequency in many energies. The “hotter” colored areas in the bottom figure represent areas of higher energy. Run Matlab demos is capable.

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Human hearing • This video of the human ear highlights the multiple frequencies in a sound. http://www.youtube.com/watch?v=ahCbGjasm_E http://www.youtube.com/watch?v=0jyxhozq89g • Human hearing is in the range 20-20,000 Hz • Human speech is mostly in the range 100-3000 Hz • Human hearing is most sensitive in the range 10010,000 Hz

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Remember This A. Sound is vibration B. Sound is a mechanical wave that creates areas of high and low pressure. C. The frequency of a signal is measured in Hz (cycles/sec), and represents the number of times the signal repeats itself within a second. D. Some sounds are composed of multiple frequencies. Speech is one of those sounds. E. Human hearing is tuned into the range of human speech, so they work together. 17