Introduction Flashcards
What does a system do?
Perform an operation or transformation of a signal or waveform
What does a x2 amplifier do?
Increases the amplitude by two times
What are the two major types of waveforms?
Periodic and aperiodic
What are periodic waveforms?
-Basic unit that repeats in time
-This gives it periodicity
-Typically have strong pitch
What are the two types of periodic waveforms and how do they differ?
Simple and complex
Complex periodic waveforms are constructed from multiple sinusoids and can be constructed into multiple sinusoids
What is a sinusoid?
A sinusoid is just a different word for a sine wave. It looks like a continuous wave
What are the characteristics of aperiodic waveforms? What are the two types?
-Do not repeat
-Can be transient (like a click or a clap) or continuous
What is sound?
The oscillation of air pressure
What happens to air molecules at high pressure vs low pressure?
High pressure- air molecules bunched up
Low pressure- air molecules spread out
How do air molecules travel through space?
As sound waves
How is sound measured?
As the pressure changes over time at one point in space
What are the essential characteristics of sinusoids?
-Have a unique shape
-Are a periodic wave (basic cycle which repeats over and over)
-Can be constructed from uniform circular motion
What are the three ways that sinusoids can differ?
- Frequency
- Amplitude
- Phase
What is phase?
Where a sinusoidal wave starts relative to some arbitrary time
What is phase measured in?
Cycles or degrees (radians)
What is a radian?
If you were to wrap the length of the radius over a circle, the radian is the angle formed at the centre of that circle
How many radians is 360 ̊, 180 ̊ and 90 ̊?
360 ̊ = 2π rads
180 ̊ = π rads
90 ̊ = π/2 rads
What is the frequency?
A measure of how fast the sinusoid is repeating
What is the period?
The time taken to complete one cycle of the wave
What is the mathematical relationship between frequency and period?
Frequency= 1/ period
Period= 1/ Frequency
How does an increase in frequency (and consequent decrease in period) affect pitch?
-Subjective pitch increases
-As the sine wave gets faster in frequency the pitch gets higher
What is the amplitude?
-Specifies how loud a sound is
-Increases in amplitude lead to increases in perceived loudness
What are simple measures of amplitude?
- Height of the peak
- Peak to peak amplitude
What is the problem with peak measures?
They don’t accurately reflect the energy in a waveform
What is the root-mean-square (rms)?
-A measure of the energy, applicable to all waveforms
-A sinusoid and its square
How is the root-mean-square calculated?
-Square all the values of the wave
-Take the average area under the curve
-Take the square root
What is meant by dB SPL?
-Decibel of sound pressure level
-The intensity of a sound
-The smallest audible sound humans can generally hear is 0 dB SPL (hearing threshold)
How is dB SPL calculated?
-Pressure of a wave is that we measure is divided by 20μPa
Why is 20μPa used in the dB SPL calculation?
-20μPa is the standard reference pressure
-It is approximately equal to human threshold
What is the point of a log scale?
Log scales convert exponential changes into linear ones
Are pressure and dB SPL linear or logarithmic?
-Pressure (in pascals) is a linear measure
-dB SPL is a logarithmic measure
Why is a logarithmic unit (dB) used to measure the intensity of a sound?
-Our perception of changes in sound amplitude is based on ratios/ proportions which is closer to a logarithmic scale
-For example, there is an obviously noticable change between a 1 kHz sinusoid of 50μPa and 100μPa
-However adding one 1Pa to a 50μPa sound it is only 1.000005 Pa which is an indistinguishable change
What is the minimum change in dB needed to distinguish a difference in the loudness of a sound?
1 dB
Equal steps on a dB scale correspond to….
Equal ratios on the linear scale
