Harmonics and Overtones Waveforms / Wave Interaction Phase Concepts / Comb Filtering Beat Frequencies / Noise AUD202 Audio and Acoustics Theory.

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Presentation transcript:

Harmonics and Overtones Waveforms / Wave Interaction Phase Concepts / Comb Filtering Beat Frequencies / Noise AUD202 Audio and Acoustics Theory

Last Week > Frequency and Dynamic Ranges of Hearing Frequency / Wavelength / Period / Speed

Upcoming Assessments Week 8 - NIHL Report Week 11 - Sound Observations Report Week 13 - Exam

Units of Measurement = velocity of sound (in metres per second) = wavelength (in metres) = frequency in Hertz (Hertz is cycles per second) = period of one cycle (in seconds)

HARMONICS & OVERTONES

Harmonics are integer multiples of the fundamental frequency.

Harmonics For example, if the fundamental frequency is 200Hz, the harmonics would be: 200Hz 400Hz 600Hz 800Hz 1000Hz Fundamental frequency 2 nd harmonic 3 rd harmonic 4 th harmonic 5 th harmonic

An overtone is any frequency higher than the fundamental frequency of a sound..

SIMPLE WAVEFORMS

Fundamental frequency only, no harmonics Sine Wave

Odd and even harmonics at inverse amplitudes Sawtooth Wave

Odd harmonics at inverse amplitudes Square Wave

Odd harmonics at inverse squared amplitudes Triangle Wave

Making a sawtooth from a sine wave A sawtooth wave's sound is harsh and clear and its spectrum contains both even and odd harmonics of the fundamental frequency

Simple Harmonic Motion Constant frequency without regard to amplitude

Simple Harmonic Motion

PHASE

Phase Concepts The word ‘Phase’ is used to describe a specific location in a cycle of a periodic (repeating) wave “In phase”, “out of phase” and “completely out of phase” are terms used to describe relative positions of a wave cycle

Phase Concepts

Phase Angles

Wave Interaction Two sine waves with the same amplitude and frequency can add either destructively or constructively depending on their relative phase

Two sine waves travelling in opposite directions can create a standing wave

Beat Frequencies

When two sound waves of different (but close) frequencies are played together, the alternating constructive and destructive interference causes an oscillation of the resulting waveform frequency 1 – frequency 2 = Beat frequency 502 Hz Hz = 2 beats per second

COMB FILTERING

Comb filtering is caused by a wave combining with a delayed version of itself

Comb Filtering A wave delayed by 180 degrees (half a wavelength) results in the fundamental frequency of cancellation. Frequencies delayed by 1.5x, 2.5x, 3.5x the wavelength will cancel, while whole number multiples (1, 2, 3 etc) will reinforce.

Comb Filtering A wave delayed by half a wavelength results in the fundamental frequency of cancellation.

Single signal, no comb filter issues

1ms delayed version of the signal added

Comb Filtering Common causes of comb filtering: 1.Two microphones at different distances from the same source. 2.Reflective nearby surface causing a reflected sound to arrive at the microphone slightly after the direct sound. 3.Two identical sounds in a DAW with a 1 to 10ms delay

WHITE NOISE & PINK NOISE

Noise White noise: Equal energy per frequency Pink noise: Equal energy per octave Pink noise is simply White noise with a ‘pinking filter’ added (-3dB/octave roll off)

Speed Writing Exercise List anything that might cause NIHL List occupations where NIHL might be a problem List ways to avoid NIHL

Next Week > Sound Envelopes Instrument Acoustics