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Harmonics and Overtones Waveforms / Wave Interaction Phase Concepts / Comb Filtering

AUD202 Audio and Acoustics Theory. Harmonics and Overtones Waveforms / Wave Interaction Phase Concepts / Comb Filtering Beat Frequencies / Noise. Last Week >. Frequency and Dynamic Ranges of Hearing Frequency / Wavelength / Period / Speed. Upcoming Assessments. Week 8 - NIHL Report

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Harmonics and Overtones Waveforms / Wave Interaction Phase Concepts / Comb Filtering

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

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

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

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

  5. HARMONICS & OVERTONES

  6. Harmonics are integer multiples of the fundamental frequency.

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

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

  9. SIMPLE WAVEFORMS

  10. Sine Wave Fundamental frequency only, no harmonics

  11. Sawtooth Wave Odd and even harmonics at inverse amplitudes

  12. Square Wave Odd harmonics at inverse amplitudes

  13. Triangle Wave Odd harmonics at inverse squared amplitudes

  14. 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

  15. Simple Harmonic Motion Constant frequency without regard to amplitude

  16. Simple Harmonic Motion

  17. PHASE

  18. 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

  19. Phase Concepts

  20. Phase Angles

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

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

  23. Beat Frequencies

  24. 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 - 500 Hz = 2 beats per second

  25. COMB FILTERING

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

  27. 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.

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

  29. Single signal, no comb filter issues

  30. 1ms delayed version of the signal added

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

  32. WHITE NOISE & PINK NOISE

  33. 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)

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

  35. Next Week > Sound Envelopes Instrument Acoustics

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