S&H: lecture III-Exam 1

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Acoustics Info continued

3 CHARACTERISTICS OF SOUND (how we perceive them)

FREQUENCY (pitch)
INTENSITY (loudness)
PERIODICITY/SPECTRUM (quality)

1) What is FREQUENCY?

2) FREQUENCY and its relationship to PITCH:

1) The number of complete cycles of vibration occurring in a second.

2) Not linear; At higher frequencies, it takes more frequency change to get an equivalent pitch change.

--From middle C to C sharp; less frequency change than from High C to C sharp.

FREQUENCY / PITCH expanded:

Rougher sounds are perceived as lower pitch than clearer sounds: its frequency

Lowest to highest frequency the human ear can detect: 20 to 20K Hz.

Usable range (what we use day to day): 100 Hz - 5K Hz.

Speech: 80 Hz - 500 Hz;

Noises for consonants: 80 - 500 Hz

We measure Frequency with Hz, and we measure Pitch with:

PERIOD; a 100 hz tone is 1/100th sec (low pitch)

--Most pitch perception: periodic complexes, or pure tones
--You can have perception of pitch for nonperiodic complex tones;

1) What is INTENSITY?


2)INTENSITY (loudness) is directly related to:

1) Magnitude of sound expressed in power or pressure;

--The underlying physical (acoustic) characteristic of a sound that leads to our perception of a sounds' loudness.

2) amplitude (distance away from point of rest)

How do we measure Intensity?

In POWER: Watt/cm squared (a watt is a flow of electricity)

In PRESSURE (force over surface area)--how we measure Intensity in speech: dynes/ cm squared.

The dB scale:

--A logarithmic ratio scale comparing one sound to another; the scale converts a large range of sounds the ear is sensitive to into manageable numbers;

smaller value scale, in which each dB is equivalent into a just noticeable difference.

The dB scale formula, and what it means:

dB SPL = 20 log 10 P1/P2

--Logarithm is how many times a number must be multiplied by itself to give you another number; in this case, log to the base 10.

For ex: 20 log 10 100/1 = 20 * 2 = 40
Answer = 40 dB SLP

--So when you've got a sound whose pressure is 100 time greater than another sound, the solution = 2, b/c 10 squared = 100. So 20 * 2 = 40 db SPL.

Another ex: : 20 log 10 1000/1 = 20 * 3 = 60.
Answer = 60 db SPL.

1) SPECTRUM (quality)

a) what is the lowest spectrum of sound?

1) what frequencies comprise any sound; how we distinguish between sounds (for ex, flute & piano have different spectrum.)

a) a single frequency

b) PERIODICITY (paired with Spectrum)

2) whether or not the pattern or oscillation of the sound-wave repeats, or how it is repeating

--pure tones are only tones whose periodicity is same cycle to cycle

Oscillation

--synonymous with vibration

--when my voice oscillates, the medium (air molecules) around me oscillates.

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